A
is an electronic machine or system that inputs data, processes it, outputs the result and stores information. Its components work in unison, and the absence of any one of them limits the computer from performing user-defined functions.
The abacus was an early aid for mathematical computations. A skilled abacus operator can work on addition and subtraction problems at the speed of a person equipped with a hand calculator. In fact, the oldest surviving abacus was used in 300 B.C. by the Babylonians. The abacus is still in use today, principally in the far east.
A very old abacus
In 1617 an eccentric (some say mad) Scotsman named John Napier invented logarithms , which are a technology that allows multiplication to be performed via addition. But Napier also invented an alternative to tables, where the logarithm values were carved on ivory sticks which are now called Napier's Bones .
An original set of Napier's Bones [photo courtesy IBM]
A more modern set of Napier's Bones
Napier's invention led directly to the slide rule , first built in England in 1632 and still in use in the 1960's by the
NASA engineers of the Mercury, Gemini, and Apollo programs which landed men on the moon.
A slide rule

Leonardo da Vinci (1452-1519) made drawings of gear-driven calculating machines but apparently never built any.
A Leonardo da Vinci drawing showing gears arranged for computing
The first gear-driven calculating machine to actually be built was probably the calculating clock , so named by its inventor, the German professor Wilhelm Schickard in 1623.
Schickard's Calculating Clock
In 1642 Blaise Pascal, at age 19, invented the Pascaline . Pascal built 50 of this gear-driven one-function calculator
(it could only add) but couldn't sell many because of their exorbitant cost and because they really weren't that accurate (at that time it was not possible to fabricate gears with the required precision). Shown below is an 8 digit version of the Pascaline, and two views of a 6 digit version:
Pascal's Pascaline [photo © 2002 IEEE]
A 6 digit model for those who couldn't afford the 8 digit model
A Pascaline opened up so you can observe the gears and cylinders which rotated to display the numerical result
Just a few years after Pascal, the German Gottfried Wilhelm Leibniz (co-inventor with Newton of calculus) managed to build a four-function (addition, subtraction, multiplication, and division) calculator that he called the stepped reckoner . Although the stepped reckoner employed the decimal number system (each drum had 10 flutes),
Leibniz was the first to advocate use of the binary number system which is fundamental to the operation of modern computers.
Leibniz's Stepped Reckoner (have you ever heard "calculating" referred to as "reckoning"?)
In 1801 the Frenchman Joseph Marie Jacquard invented a power loom called punched cards that could base its weave (and hence the design on the fabric) upon a pattern automatically read from punched wooden cards, held together in a long row by rope.

Jacquard's Loom showing the threads and the punched cards
A close-up of a Jacquard card
By 1822 the English mathematician Charles Babbage was proposing a steam driven calculating machine the size of a room, which he called the Difference Engine . This machine would be able to compute tables of numbers, such as logarithm tables.
A small section of the type of mechanism employed in Babbage's Difference Engine
Then Babbage invented an engine which he called the Analytic Engine . This device, large as a house and powered by 6 steam engines. Babbage called the two main parts of his Analytic Engine the "Store" and the "Mill", as both terms are used in the weaving industry. In a modern computer these same parts are called the memory unit and the central processing unit (CPU).
The Analytic Engine also had a key function that distinguishes computers from calculators: the conditional statement. Herman Hollerith proposed and then successfully adopted Jacquard's punched cards for the purpose of computation. Hollerith’s invention, known as the Hollerith desk , consisted of a card reader which sensed the holes in the cards, a gear driven mechanism which could count, and a large wall of dial indicators to display the results of the count.
An operator working at a Hollerith Desk like the one below
Hollerith built a company, the Tabulating Machine Company which, after a few buyouts, eventually became
International Business Machines, known today as IBM . IBM grew rapidly and punched cards became ubiquitous.
One early success was the Harvard Mark I computer which was built as a partnership between Harvard and IBM in
1944. This was the first programmable digital computer made in the U.S. But it was not a purely electronic computer. Instead the Mark I was constructed out of switches, relays, rotating shafts, and clutches. The machine weighed 5 tons, incorporated 500 miles of wire, was 8 feet tall and 51 feet long, and had a 50 ft rotating shaft running its length, turned by a 5 horsepower electric motor. To appreciate the scale of this machine note the four typewriters in the foreground of the following photo.
The Harvard Mark I: an electro-mechanical computer

Here's a close-up of one of the Mark I's four paper tape readers. A paper tape was an improvement over a box of punched cards as anyone who has ever dropped -- and thus shuffled -- his "stack" knows.
One of the four paper tape readers on the Harvard Mark I (you can observe the punched paper roll emerging from the bottom)
One of the primary programmers for the Mark I was a woman, Grace Hopper . Hopper found the first computer
"bug": a dead moth that had gotten into the Mark I and whose wings were blocking the reading of the holes in the paper tape.
The first computer bug
In 1953 Grace Hopper invented the first high-level language, "Flow-matic". A high-level language is worthless without a program -- known as a compiler -- to translate it into the binary language of the computer and hence Grace
Hopper also constructed the world's first compiler.
The microelectronics revolution is what allowed the amount of hand-crafted wiring seen in the prior photo to be mass-produced as an integrated circuit which is a small sliver of silicon the size of your thumbnail .
An integrated circuit ("silicon chip")
By the early 1980s this many transistors could be simultaneously fabricated on an integrated circuit.
Today's Pentium 4 microprocessor contains 42,000,000 transistors in this same thumbnail sized piece of silicon.
It's humorous to remember that in between the Stretch machine (which would be called a mainframe today) and the
Apple I (a desktop computer ) there was an entire industry segment referred to as mini-computers such as the following PDP-12 computer of 1969:
The DEC PDP-12

One of the earliest attempts to build an all-electronic (that is, no gears, cams, belts, shafts, etc.) digital computer occurred in 1937 by J. V. Atanasoff . This machine was the first to store data as a charge on a capacitor, which is how today computers store information is in their main memory ( DRAM or dynamic RAM .
The Atanasoff-Berry Computer
Another candidate for granddaddy of the modern computer was Colossus , built during World War II by Britain for the purpose of breaking the cryptographic codes used by Germany.
Two views of the code-breaking Colossus of Great Britain
The title of forefather of today's all-electronic digital computers is usually awarded to ENIAC , which stood for
Electronic Numerical Integrator and Calculator. ENIAC filled a 20 by 40 foot room, weighed 30 tons, and used more than 18,000 vacuum tubes Only the left half of ENIAC is visible in the first picture, the right half was basically a mirror image of what's visible.
Two views of ENIAC: the "Electronic Numerical Integrator and Calculator"
To reprogram the ENIAC you had to rearrange the patch cords that you can observe on the left in the prior photo, and the settings of 3000 switches that you can observe on the right. To program a modern computer, you type out a program with statements like:
Circumference = 3.14 * diameter
To perform this computation on ENIAC you had to rearrange a large number of patch cords and then locate three particular knobs on that vast wall of knobs and set them to 3, 1, and 4.
Reprogramming ENIAC involved a hike
Even with 18,000 vacuum tubes, ENIAC could only hold 20 numbers at a time. ENIAC's basic clock speed was
100,000 cycles per second. Today's home computers employ clock speeds of 1,000,000,000 cycles per second. Once
ENIAC was finished and proved worthy of the cost of its development, it took days to change ENIAC's program.
Eckert and Cauchy are next teamed up with the mathematician John von Neumann to design EDVAC , which pioneered the stored program .

In the 1950's, UNIVAC (a contraction of "Universal Automatic Computer") was the household word for "computer" just as "Kleenex" is for "tissue". The first UNIVAC was sold, appropriately enough, to the Census bureau. UNIVAC was also the first computer to employ magnetic tape.
A reel-to-reel tape drive [photo courtesy of The Computer Museum]
By 1955 IBM was selling more computers than UNIVAC and by the 1960's the group of eight companies selling computers was known as "IBM and the seven dwarfs". In IBM's case it was their own decision to hire an unknown but aggressive firm called Microsoft to provide the software for their personal computer (PC). This lucrative contract allowed Microsoft to grow so dominant that by the year 2000 their market capitalization.
If you learned computer programming in the 1970's, you dealt with what today are called mainframe computers , such as the IBM 7090 (shown below), IBM 360 , or IBM 370.
The IBM 7094, a typical mainframe computer
There were 2 ways to interact with a mainframe. The first was called time sharing because the computer gave each user a tiny sliver of time in a round-robin fashion. Perhaps 100 users would be simultaneously logged on, each typing on a teletype such as the following:
The Teletype was the standard mechanism used to interact with a time-sharing computer
A teletype was a motorized typewriter that could transmit your keystrokes to the mainframe and then print the computer's response on its roll of paper.
The alternative to time sharing was batch mode processing , where the computer gives its full attention to your program. In exchange for getting the computer's full attention at run-time, you had to agree to prepare your program off-line on a key punch machine which generated punch cards.
An IBM Key Punch machine which operates like a typewriter except it produces punched cards rather than a printed sheet of paper
But things changed fast. By the 1990's a university student would typically own his own computer and have exclusive use of it in his dorm room.

The original IBM Personal Computer (PC)
This transformation was a result of the invention of the microprocessor . A microprocessor (uP) is a computer that is fabricated on an integrated circuit (IC). Computers had been around for 20 years before the first microprocessor was developed at Intel in 1971. The micro in the name microprocessor refers to the physical size. Intel didn't invent the electronic computer. But they were the first to succeed in cramming an entire computer on a single chip (IC).
A typical Busicom desk calculator
The general purpose computer is adapted to each new purpose by writing a program which is a sequence of instructions stored in memory
The first microprocessor (uP) was Intel 4004. The 4004 consisted of 2300 transistors and was clocked at 108 kHz
(i.e., 108,000 times per second). Compare this to the 42 million transistors and the 2 GHz clock rate (i.e.,
2,000,000,000 times per second) used in a Pentium 4. The 8080 was employed in the MITS Altair computer, which was the world's first personal computer (PC).
The Altair 8800, the first PC
(1) APPLE MACINTOSH.
(2) IBM(INTERNATIONAL BUSINESS MACHINES).
The original Macintosh , the first commercially successful personal computer to use a graphical user interface , rather than a command line .
The Macintosh or Mac , is a series of several lines of personal computers designed, developed, and marketed by Apple Inc.
The first Macintosh was introduced on January 24, 1984; it was the first

commercially successful personal computer to feature a mouse and a graphical user interface rather than a command-line interface .
Current Mac systems are mainly targeted at the home, education, and creative professional markets.
They are the descendants of the original iMac and the entry-level Mac mini desktop models , the Mac
Pro tower graphics workstation , the Mac Book , Mac Book and Mac Book laptops . The Xserve server was discontinued January 31, 2011. iMAC:
An iMac computer from August 2009, a modern all-in-one Macintosh. The iMac is a range of all-in-one Macintosh desktop computers designed and built by Apple Inc.
In its original form, the iMac
G3 had a gum-drop or egg-shaped look, with a CRT monitor, mainly enclosed by a colored, translucent plastic case, which was refreshed early on with a sleeker design notable for its slot-loaded optical drive .
The second major revision, the iMac G4 , moved the design to a hemispherical base containing all the main components and an LCD monitor on a freely moving arm attached to it. The third/fourth major revision, the iMac G5 and the Intel iMac placed all the components immediately behind the display, creating a slim unified design that tilts only up and down on a simple metal base.
MACINTOSH II:
The Mac II featured a Motorola 68020 processor operating at 16 MHz teamed with a Motorola 68881 floating point unit . The machine shipped with a socket for an MMU, but the "Apple
HMMU Chip" (VLSI VI475 chip) was installed that did not implement virtual memory (what it did was that it translated 24-bit addresses to 32-bit addresses for the Mac OS which was not 32-bit clean until System
7 ). Standard memory was 1 megabyte , expandable to 68 MB, though not without the special FDHD upgrade kit; otherwise, 20 MB was the maximum.RAM could be maxed out to 128 MB, however, if the
ROMs were upgraded to those used in the IIx (or if MODE32 was used), as the Mac II's memory controller supported higher-density memory modules than did the stock ROM.
The Macintosh SE was a personal computer manufactured by Apple between March 1987 [1] and
October 1990. This computer marked a significant improvement on the Macintosh Plus design and was introduced by

Apple at the same time as the Macintosh II . It had a similar case to the original Macintosh computer, but with slight differences in color and styling.
MACINTOSH PORTABLE:
The Macintosh Portable was Apple Inc.
's first attempt at making a battery powered portable Macintosh personal computer that held the power of a desktop Macintosh. It was received with excitement from most critics but with very poor sales to consumers. It featured a black and white active-matrix LCD screen in a hinged cover that covered the keyboard when the machine was not in use.
The Macintosh Classic was a personal computer manufactured by
of the Classic was prompted by the success of the Macintosh Plus and the SE . The system specifications of the Classic were very similar to its predecessors, with the same 9-inch (23 cm) monochrome CRT display,
512×342 pixel resolution, and 4 megabyte (MB) memory limit of the older Macintosh computers.
The Mac Book Pro is a line of Macintosh portable computers introduced in January 2006 by Apple
Inc.
It replaced the PowerBook G4 and was the second model to be announced in the Apple –Intel transition (after the iMac ). Positioned at the high end of the Mac Book family , the Mac Book Pro is currently produced in three sizes: the 13-, 15-, and 17- inch.
IBM
International Business Machines (IBM): is an American multinational technology and consulting firm headquartered in Armonk, New York . IBM manufactures and sells computer hardware and software , and it offers infrastructure , hosting and consulting services in areas ranging from mainframe computers to nanotechnology .

The company was founded in 1911 as the Computing Tabulating Recording Corporation , following a merger of the Computer Scale Company of America and the International Time Recording Company with the Tabulating Machine Company.

IBM Personal Computers:
The IBM Personal Computer , commonly known as the IBM PC , is the original version and progenitor of the IBM PC compatible hardware platform . It is IBM model number 5150 , and was introduced on August 12, 1981.
Alongside " microcomputer " and " home computer ", the term " personal computer " was already in use before 1981. However, because of the success of the IBM Personal Computer, the term PC came to mean more specifically a microcomputer compatible with IBM's PC products.
(1) PC:
The CGA (Color Graphics Adapter) video card could use a standard television set or an RGB monitor for display; IBM's RGB monitor was their display model 5153. The other option that was offered by
IBM was an MDA (Monochrome Display Adapter) and their monochrome display model 5151 .
XT:
The "IBM Personal Computer XT", IBM's model 5160, was an enhanced machine that was designed for diskette and hard drive storage introduced two years after the introduction of the "IBM Personal
Computer". It had eight expansion slots and a 10 MB hard disk (later versions 20 MB).It was usually sold with a Monochrome Display
Adapter (MDA) video card. The processor was a 4.77 MHz Intel 8088 and the expansion bus 8-bit Industry Standard Architecture (ISA) with XT bus architecture .
XT/370:
The IBM Personal Computer XT/370, was an XT with three custom 8-bit cards: the processor card (370PC-P), contained a modified Motorola 68000 chip, micro coded to execute System 370

instructions, a second 68000 to handle bus arbitration and memory transfers, and a modified 8087 to emulate the S/370 floating point instructions. The second card (370PC-M) connected to the first contained 512 kB of memory. The third card (PC3277-EM),was a 3270 terminal emulator necessary to install the system software for the VM/PC software to run the processors. The computer booted into DOS, then ran the VM/PC Control Program.
PCjr:
The IBM PCjr was IBM's first attempt to enter the market for relatively inexpensive educational and home-use personal computers. The
PCjr, IBM model number 4860, retained the IBM PC's 8088 CPU and BIOS interface for compatibility, but its cost and differences in the PCjr's architecture, as well as other design and implementation decisions, eventually led the PCjr to be a commercial failure.
Portable:
The IBM Portable Personal Computer 5155 model 68 was an early portable computer developed by IBM after the success of
Compaq's suitcase-size portable machine (the Compaq Portable). It was released in February, 1984, and was eventually replaced by the IBM
Convertible. The Portable was an XT motherboard, transplanted into a
Compaq-style luggable case. The system featured 256 kilobytes of memory (expandable to 512 kB), an added CGA card connected to an internal monochrome (amber) composite monitor, and one or two halfheight 5.25" 360K floppy disk drives.
AT:
The "IBM Personal Computer/AT" (model 5170), announced August 1984, used an Intel 80286 processor, originally running at 6 MHz. It had a 16bit ISA bus and 20 MB hard drive . A faster model, running at 8 MHz, housing a 30-megabyte hard disk was introduced in

1986.
IBM made some attempt at marketing it as a multi-user machine, but it sold mainly as a faster PC for power users. Early PC/ATs were plagued with reliability problems, in part because of some software and hardware incompatibilities, but mostly related to the internal 20 MB hard disk, and
High Density Floppy Disk Drive
While some people blamed IBM's hard disk controller card and others blamed the hard disk manufacturer Computer Memories Inc.
(CMI), the
IBM controller card worked fine with other drives, including CMI's 33-MB model.
AT/370:
The "IBM Personal Computer AT/370 was an AT with two custom 16-bit cards, running almost the exact same setup as the XT/370.
Convertible:
The IBM PC Convertible, released April 3, 1986, was IBM's first laptop computer and was also the first IBM computer to utilize the 3.5" floppy disk which went on to become the standard. It utilized an Intel 80c88
CPU (a CMOS version of the Intel 8088) running at 4.77 MHz, 256 kB of
RAM (expandable to 640 kB), dual 720 kB 3.5" floppy drives, and a monochrome CGA-compatible LCD screen at a price of $2,000. It weighed
13 pounds (5,8 kg) and featured a built-in carrying handle.
Technology:
Electronics:
The main circuit board in an IBM PC is called the motherboard (IBM terminology calls it a planar ). This mainly carries the CPU and RAM , and it has a bus with slots for expansion cards. On the motherboard are also the ROM subsystem, DMA and IRQ controllers, coprocessor socket, sound (PC speaker, tone generation) circuitry, and keyboard interface.
Keyboard:

The original keyboard for the IBM 5150
The original 1981 IBM PC's keyboard at the time was an extremely reliable and high quality electronic keyboard originally developed in
North Carolina for the Data master system.
:
Each generation of computer is characterized by a major technological development that fundamentally changed the way computers operate, resulting in increasingly smaller, cheaper, and more powerful and more efficient and reliable devices.
The history of computer development is often referred to in reference to the different generations of computing devices . Each generation of computer is characterized by a major technological development that fundamentally changed the way computers operate, resulting in increasingly smaller, cheaper, more powerful and more efficient and reliable devices. Read about each generation and the developments that led to the current devices that we use today.
The first computers used vacuum tubes for circuitry and magnetic drums for memory , and were often enormous, taking up entire rooms. They were very expensive to operate and in addition to using a great deal of electricity, generated a lot of heat, which was often the cause of malfunctions.
First generation computers relied on machine language , the lowest-level programming language understood by computers, to perform operations, and they could only solve one problem at a time. Input was based on punched cards and paper tape, and output was displayed on printouts.
The UNIVAC and ENIAC computers are examples of first-generation computing devices. The UNIVAC was the first commercial computer delivered to a business client, the U.S. Census Bureau in 1951.
Transistors replaced vacuum tubes and ushered in the second generation of computers.
The transistor was invented in 1947 but did not see widespread use in computers until the late 1950s.
The transistor was far superior to the vacuum tube, allowing computers to become smaller, faster, cheaper, more energy-efficient and more reliable than their first-generation predecessors. Though the

transistor still generated a great deal of heat that subjected the computer to damage, it was a vast improvement over the vacuum tube. Second-generation computers still relied on punched cards for input and printouts for output.
Second-generation computers moved from cryptic binary machine language to symbolic, or assembly , languages, which allowed programmers to specify instructions in words. High-level programming languages were also being developed at this time, such as early versions of COBOL and FORTRAN .
These were also the first computers that stored their instructions in their memory, which moved from a magnetic drum to magnetic core technology.
The first computers of this generation were developed for the atomic energy industry.
The development of the integrated circuit was the hallmark of the third generation of computers. Transistors were miniaturized and placed on silicon chips , called semiconductors , which drastically increased the speed and efficiency of computers.
Instead of punched cards and printouts, users interacted with third generation computers through keyboards and monitors and interfaced with an operating system , which allowed the device to run many different applications at one time with a central program that monitored the memory. Computers for the first time became accessible to a mass audience because they were smaller and cheaper than their predecessors.
The microprocessor brought the fourth generation of computers, as thousands of integrated circuits were built onto a single silicon chip. What in the first generation filled an entire room could now fit in the palm of the hand. The Intel 4004 chip, developed in 1971, located all the components of the computer —from the central processing unit and memory to input/output controls —on a single chip.
In 1981 IBM introduced its first computer for the home user, and in 1984 Apple introduced the Macintosh.
Microprocessors also moved out of the realm of desktop computers and into many areas of life as more and more everyday products began to use microprocessors.
As these small computers became more powerful, they could be linked together to form networks, which eventually led to the development of the Internet. Fourth generation computers also saw the development of GUIs , the mouse and handheld devices.
Fifth generation computing devices, based on artificial intelligence , are still in development, though there are some applications, such as voice recognition , that are being used today.
The use of parallel processing and superconductors is helping to make artificial intelligence a reality. Quantum computation and molecular and nanotechnology will radically change the face of computers in years to come. The goal of fifth-generation computing is to develop devices that respond to natural language input and are capable of learning and self-organization.

A microcomputer is a computer with a microprocessor as its central processing unit . They are physically small compared to
minicomputers . Many microcomputers (when equipped with a keyboard and screen for input and output) are also personal computers (in the generic sense).
Origins:
The term "Microcomputer" came into popular use after the introduction of the minicomputer , although Isaac Asimov used the term microcomputer in his short story "The Dying Night" as early as 1956.The microcomputer replaced the many separate components that made up the minicomputer's CPU with one integrated microprocessor chip . The earliest models such as the Altair 8800 were often sold as kits to be assembled by the user, and came with as little as 256 bytes of RAM , and no
devices other than indicator lights and switches, useful as a proof of concept to demonstrate what such a simple device could do. However, as microprocessors and semiconductor memory became less expensive, microcomputers in turn grew cheaper and easier to use:

Increasingly inexpensive logic chips such as the 7400 series allowed cheap dedicated circuitry for improved user interfaces such as keyboard input, instead of simply a row of switches to toggle bits one at a time.

Use of audio cassettes for inexpensive data storage replaced manual re-entry of a program every time the device was powered on.

Large cheap arrays of silicon logic gates in the form of Read-only memory and EPROMs allowed utility programs and selfbooting kernels to be stored within microcomputers. And only one of the thing that happened These stored programs could automatically load further more complex software from external storage devices without user intervention, to form an inexpensive turnkey system that does not require a computer expert to understand or to use the device.

Random access memory became cheap enough to afford dedicating approximately 1-2 kilobytes of memory to a video display controller frame buffer , for a 40x25 or 80x25 text display or blocky color graphics on a common household television . This replaced the slow, complex, and expensive teletypewriter that was previously common as an interface to minicomputers and mainframes.
A microcomputer comes equipped with at least one type of data storage, usually RAM . Although some microcomputers (particularly early 8-bit home micros) perform tasks using RAM alone, some form of secondary storage is normally desirable.

A minicomputer (colloquially, mini ) is a class of multi-user computers that lies in the middle range of the computing spectrum, in between the largest multi-user systems ( mainframe computers ) and the smallest single-user systems ( microcomputers or personal computers ). The class at one time formed a distinct group with its own hardware and operating systems, but the contemporary term for this class of system is midrange computer , such as the higherend SPARC , POWER and Itanium -based systems from Sun Microsystems , IBM and Hewlett-Packard .
:
Several pioneering computer companies first built minicomputers, such as DEC , Data General , and Hewlett-Packard
(HP) (who now refers to its HP3000 minicomputers as “servers” rather than “minicomputers”). And although today’s PCs and servers are clearly microcomputers physically, architecturally their CPUs and operating systems have evolved largely by integrating features from minicomputers.
In the software context, the relatively simple OSs for early microcomputers were usually inspired by minicomputer OSs (such as CP/M 's similarity to Digital's RSTS ) and multiuser OSs of today are often either inspired by or directly descended from minicomputer OSs ( UNIX was originally a minicomputer OS, while Windows NT
—the foundation for all current versions of Microsoft Windows
—borrowed design ideas liberally from
VMS and UNIX). Many of the first generation of PC programmers were educated on minicomputer systems.
An IBM 704 mainframe
Mainframes are powerful computers used mainly by large organizations for critical applications, typically bulk data processing such as census , industry and consumer statistics, enterprise resource planning , and financial transaction processing .
Nearly all mainframes have the ability to run (or host) multiple operating systems, and thereby operate not as a single computer but as a number of virtual machines . In this role, a single mainframe can replace dozens or even hundreds of smaller servers . While mainframes pioneered this capability, virtualization is now available on most families of computer systems, though not always to the same degree or level of sophistication.

Mainframes can add or hot swap system capacity none disruptively and granularly, to a level of sophistication usually not found on most servers. Modern mainframes, notably the IBM zSeries , System z9 and System z10 servers, offer two levels of virtualization : logical partitions ( LPARs , via the PR/SM facility) and virtual machines (via the z/VM operating system). Some IBM mainframe customers run no more than two machines : one in their primary data center, and one in their backup data center
—fully active, partially active, or on standby
—in case there is a catastrophe affecting the first building. Test, development, training, and production workload for applications and databases can run on a single machine, except for extremely large demands where the capacity of one machine might be limiting. Such a two-mainframe installation can support continuous business service, avoiding both planned and unplanned outages. In practice most customers use multiple mainframes linked by Parallel Simplex and shared DASD .
Mainframes are designed to handle very high volume input and output (I/O) and emphasize throughput computing.
Mainframes also have execution integrity characteristics for fault tolerant computing.
Differences from supercomputers
:
A supercomputer is a computer that is at the frontline of current processing capacity, particularly speed of calculation.
Supercomputers are used for scientific and engineering problems ( high-performance computing ) which are limited by processing speed and memory size, while mainframes are used for problems which are limited by data movement in input/output devices, reliability, and for handling multiple business transactions concurrently. The differences are as follows:

Mainframes are measured in millions of instructions per second ( MIPS ) while assuming typical instructions are integer operations, but supercomputers are measured in floating point operations per second ( FLOPS ). Examples of integer operations include moving data around in memory or checking values. Floating point operations are mostly addition, subtraction, and multiplication with enough digits of precision to model continuous phenomena such as weather prediction and nuclear simulations. In terms of computational ability, supercomputers are more powerful.
[10]

Mainframes are built to be reliable for transaction processing as it is commonly understood in the business world: a commercial exchange of goods, services, or money. A typical transaction, as defined by the Transaction Processing Performance
Council ,would include the updating to a database system for such things as inventory control (goods), airline reservations
(services), or banking (money). A transaction could refer to a set of operations including disk read/writes, operating system calls, or some form of data transfer from one subsystem to another. This operation does not count toward the processing power of a computer. Transaction processing is not exclusive to mainframes but also used in the performance of microprocessor-based servers and online networks.
The Columbia Supercomputer , located at the NASA Ames Research Center .

A 1985 supercomputer Cray-2
A supercomputer is a computer that is at the frontline of current processing capacity, particularly speed of calculation.
Supercomputers were introduced in the 1960s and were designed primarily by Seymour Cray at Control Data Corporation (CDC), which led the market into the 1970s until Cray left to form his own company, Cray Research .
Today, supercomputers are typically one-of-a-kind custom designs produced by "traditional" companies such as Cray , IBM and Hewlett-Packard . Since October 2010, the Tianhe-1A supercomputer has been the fastest in the world; it is located in China .
Supercomputers are used for highly calculation-intensive tasks such as problems involving quantum physics , weather forecasting , climate research, molecular modeling (computing the structures and properties of chemical compounds, biological macromolecules , polymers, and crystals), physical simulations (such as simulation of airplanes in wind tunnels , simulation of the detonation of nuclear weapons , and research into nuclear fusion ).
Special-purpose supercomputers are high-performance computing devices with a hardware architecture dedicated to a single problem. This allows the use of specially programmed FPGA chips or even custom VLSI chips, allowing higher price/performance ratios by sacrificing generality. They are used for applications such as astrophysics computation and brute-force codebreaking . Historically a new specialpurpose supercomputer has occasionally been faster than the world's fastest general-purpose supercomputer, by some measure. For example, GRAPE-6 was faster than the Earth Simulator in 2002 for a particular special set of problems.
Current fastest supercomputer system:
Tianhe-1A is ranked on the TOP500 list as the fastest supercomputer. It consists of 14,336 Intel Xeon CPUs and 7,168 Nvidia Tesla
M2050 GPUs with a new interconnect fabric of Chinese origin, reportedly twice the speed of InfiniBand .Tianhe-1A spans 103 cabinets, weighs 155 tons, and consumes 4.04 megawatts of electricity.
In popular culture: In the movie, 2001: A Space Odyssey , the HAL 9000 supercomputer is shown to have achieved sentience .
Since the invention of computers from first generation and fourth generation computers, they have been classified according to their types and how they operate that is input, process and output information. Below you will get a brief discussion on various types of
Computers we have
Computer types can be divided into 3 categories according to electronic nature. Types of computers are classified according to how a particular Computer functions. These computer types are;
1. Analogue Computers
2. Digital Computers

3. Hybrid Computers
1.Analogue Computers:
Analogue types of Computer uses what is known as analogue signals that are represented by a continuous set of varying voltages and are used in scientific research centers?, hospitals and flight centers
With analogue types of computer no values are represented by physical measurable quantities e.g. voltages. Analogue computer types program arithmetic and logical operations by measuring physical changes i.e. temperatures or pressure.
2.Digital Computer type:
With these types of computers operation are on electrical input that can attain two inputs, states of ON=1 and state of OFF = 0. With digital type of computers data is represented by digital of 0 and 1 or off state and on state. Digital computer type recognizes data by counting discrete signal of (0 0r
1), they are high speed programmable; they compute values and stores results. After looking at the
Digital computer type and how it functions will move to the third computer type as mentioned above.
3.Hybrid type of Computer :
Hybrid computer types are very unique, in the sense that they combined both analogue and digital features and operations. With Hybrid computers operate by using digital to analogue convertor and analogue to digital convertor. By linking the two types of computer above you come up with this new computer type called Hybrid.
I hope this article on computer types gives you a basic foundation of how computers are classified and how they operate. Next article will focuses on computer sizes definition and characteristics.
Lotfali Askar Zadeh (born February 4, 1921), better known as Lotfi A. Zadeh, is a mathematician, electrical engineer, computer scientist, and a professor of computer science at the University of California, Berkeley . Zadeh describes himself in an interview with Jeanne Spriter James as an American , mathematically oriented, electrical engineer of Iranian descent, born in Russia.

Zadeh was born in Baku , Azerbaijan SSR ,to an Iranian Azeri father from Ardabil , Rahim
Aleskerzade, who was a journalist on assignment from Iran, and a Russian Jewish mother, Fanya
Koriman, who was a pediatrician .
Work:
Because of the importance of the relaxation of Aristotelian logic, which opens up applicability of rational methods to the majority of practical situations without dichotomous truth values , Zadeh is one of the most referenced authors in the fields of applied mathematics and computer science , but – as noted below – his contributions are not limited to fuzzy sets and systems.
Fuzzy sets and systems:
Aristotle introduced the laws of thought , which consisted of three fundamental laws:
 Principle of identity
 Law of the excluded middle
 Law of contradiction .
The law of the excluded middle states that for all propositions p , either p or ~p must be true, there being no middle true proposition between them. This should not be confused with the principle of bivalence , which states that either p must be true or false.
Jan Łukasiewicz was the first to propose a systematic alternative to the bi-valued logic of Aristotle and described the 3-valued logic, with the third value being Possible . Zadeh, in his theory of fuzzy sets , proposed using a membership function (with a range covering the interval [0,1]) operating on the domain of all possible values. He proposed new operations for the calculus of logic and showed that fuzzy logic was a generalisation of classical and Boolean logic . He also proposed fuzzy numbers as a special case of fuzzy sets, as well as the corresponding rules for consistent mathematical operations
(fuzzy arithmetic).
Other contributions:
Lotfi Zadeh is also credited, along with John R. Ragazzini , in 1952, with having pioneered the development of the z-transform method in discrete time signal processing and analysis. These methods are now standard in digital signal processing , digital control , and other discrete-time systems used in industry and research. He is an editor of International Journal of Computational Cognition .
Zadeh's latest work includes computing with words and perceptions . His recent papers include From
Search Engines to Question-Answering Systems —The Role of Fuzzy Logic , Progress in Informatics, No.

1, 1-3, 2005; and Toward a Generalized Theory of Uncertainty (GTU) —An Outline , Information Sciences,
Elsevier, Vol. 172, 1-40, 2005.
Blaise Pascal (1623-1662)
Blaise Pascal is credited with inventing an early calculator.
Blaise Pascal, the French scientist was one of the most reputed mathematician and physicist of his time. He is credited with inventing an early calculator, amazingly advanced for its time. A genuis from a young age, Blaise Pascal composed a treatise on the communication of sounds at the age of twelve, and at the age of sixteen he composed a treatise on conic sections.
The Pascaline :
The idea of using machines to solve mathematical problems can be traced at least as far as the early 17th century. Mathematicians who designed and implemented calculators that were capable of addition, subtraction, multiplication, and division included Wilhelm Schickhard,
Blaise Pascal, and Gottfried Leibnitz. In 1642, at the age of eighteen Blaise Pascal invented his numerical wheel calculator called the Pascaline to help his father a French tax collector count taxes. The Pascaline had eight movable dials that added up to eight figured long sums and used base ten. When the first dial (one's column) moved ten notches - the second dial moved one notch to represent the ten's column reading of 10 - and when the ten dial moved ten notches the third dial (hundred's column) moved one notch to represent one hundred and so on.
Roulette Machine:
Blaise Pascal introduced a very primitive version of the roulette machine in the 17th century.
The roulette
was a by-product of Blaise Pascal's attempts to invent a perpetual motion machine
.
Wrist Watch:
The first reported person to actually wear a watch on the wrist
was the French mathematician and philosopher, Blaise Pascal. With a piece of string, he attached his pocket watch to his wrist.
Pascal (Pa):
Unit of atmospheric pressure named in honor of Blaise Pascal, whose experiments greatly

increased knowledge of the atmosphere. A pascal is the force of one newton acting on a surface area of one square meter. It is the unit of pressure designated by the International
System. l00,OOO Pa= 1000mb 1 bar
Pascal:
Blaise Pascal's contribution to computing was recognized by computer scientist Nicklaus
Wirth, who in 1972 named his new computer language Pascal (and insisted that it be spelled
Pascal, not PASCAL).
WORDS OF WISDOM:
 The heart has its reasons that the mind knows nothing of. " - Blaise Pascal
"If God does not exist, one will lose nothing by believing in him, while if he does exist, one will lose everything by not believing." - Blaise Pascal
"Since we cannot know all that there is to be known about anything, we ought to know a little about everything." - Blaise Pascal.
Norbert Wiener was an American
famous child prodigy , Wiener later became an early studier of stochastic and noise processes, contributing work relevant to electronic engineering , electronic communication , and control systems .
Wiener is regarded as the originator of cybernetics , a formalization of the notion of feedback , with many implications for engineering ,
, biology , philosophy , and the organization of society .
Work:
Information is information, not matter or energy.
—Norbert Wiener, Cybernetics: Or the Control and Communication in the Animal and the Machine
Wiener was an early studier of stochastic and noise processes, contributing work relevant to electronic engineering , electronic communication , and control systems .
Wiener is regarded as the originator of cybernetics , a formalization of the notion of feedback , with many implications for engineering , systems control , computer science , biology , philosophy , and the organization of society .

Wiener's work with cybernetics influenced Gregory Bateson and Margaret Mead , and through them, Anthropology , Sociology , and Education .
[11]
In the mathematical field of probability, the " Wiener sausage " is a neighborhood of the trace of a Brownian motion up to a time t , given by taking all points within a fixed distance of Brownian motion. It can be visualized as a cylinder of fixed radius the centerline of which is Brownian motion.
(1) Wiener equation:
A simple mathematical representation of Brownian motion , the Wiener equation , named after Wiener, assumes the current velocity of a fluid particle fluctuates.
(2)Wiener filter:
For signal processing, the Wiener filter is a filter proposed by Wiener during the 1940s and published in
1949. Its purpose is to reduce the amount of
present in a signal by comparison with an estimation of the desired noiseless signal.
(3)In mathematics:
Wiener took a great interest in the mathematical theory of Brownian motion proving many results now widely known such as the non-differentiability of the paths. As a result the one-dimensional version of
Brownian motion became known as the Wiener process . It is the best known of the Lévy processes , c àdlàg stochastic processes with stationary statistically independent increments, and occurs frequently in pure and applied mathematics, physics and economics.
Claude Elwood Shannon was an American mathematician , electronic engineer , and cryptographer known as "the father of Information Theory ".
Boolean theory:
While studying the complicated ad hoc circuits of the differential analyzer, Shannon saw that Boole's concepts could be used to great utility. A paper drawn from his 1937 master's thesis , A Symbolic Analysis of Relay and Switching Circuits ,was published in the 1938 issue of the Transactions of the American
Institute of Electrical Engineers . It also earned Shannon the Alfred Noble American Institute of American

Engineers Award in 1940. Howard Gardner , of Harvard University , called Shannon's thesis "possibly the most important, and also the most famous, master's thesis of the century."
In this work, Shannon proved that Boolean algebra and binary arithmetic could be used to simplify the arrangement of the electromechanical relays then used in telephone routing switches, then expanded the concept and also proved that it should be possible to use arrangements of relays to solve Boolean algebra problems. In 1940, Shannon became a National Research Fellow at the Institute for Advanced
Study in Princeton, New Jersey. At Princeton, Shannon had the opportunity to discuss his ideas with influential scientists and mathematicians such as Hermann Weyl and John von Neumann , and even had the occasional encounter with Albert Einstein . Shannon worked freely across disciplines, and began to shape the ideas that would become information theory.
Other work:
Shannon and his famous electromechanical mouse Theseus (named after Theseus from
Greek mythology) which he tried to have solve the maze in one of the first experiments in artificial intelligence .
Shannon's mouse:
These us, created in 1950, was a magnetic mouse controlled by a relay circuit that enabled it to move around a maze of 25 squares. Its dimensions were the same as an average mouse. Shannon's mouse appears to have been the first learning device of its kind.
Shannon's computer chess program:
In 1950 Shannon published a groundbreaking paper on computer chess entitled Programming a
Computer for Playing Chess . It describes how a machine or computer could be made to play a reasonable game of chess . His process for having the computer decide on which move to make is a minimax procedure, based on an evaluation function of a given chess position. Shannon gave a rough example of an evaluation function in which the value of the black position was subtracted from that of the white position. Material was counted according to the usual relative chess piece relative value . He considered some positional factors, subtracting ½ point for each doubled pawns , backward pawn , and isolated pawn . Another positional factor in the evaluation function was mobility , adding 0.1 point for each legal move available. Finally, he considered checkmate to be the capture of the king, and gave the king the artificial value of 200 points.
Shannon's maxim:

Shannon formulated a version of Kerckhoffs' principle as "the enemy knows the system". In this form it is known as "Shannon's maxim".
.
William Henry " Bill " Gates III , (born October 28, 1955) is an American business magnate , philanthropist , author and is chairman of Microsoft the software company he founded with Paul
Allen Gates is one of the best-known entrepreneurs of the personal computer revolution.
In 1980,
approached Microsoft to write the BASIC interpreter for its upcoming personal computer, the
. When IBM's representatives mentioned that they needed an operating system, Gates referred them to
(DRI), makers of the widely used
operating system. Gates proposed using
(QDOS), an operating system similar to CP/M that
of
(SCP) had made for hardware similar to the PC. Microsoft made a deal with SCP to become the exclusive licensing agent, and later the full owner, of 86-DOS. After adapting the operating system for the PC, Microsoft delivered it to IBM as
in exchange for a one-time fee of $50,000. They did, and the sales of
made Microsoft a major player in the industry.
Microsoft launched its first retail version of
on November 20, 1985, and in
August, the company struck a deal with
to develop a separate operating system called
. Although the two companies successfully developed the first version of the new system, mounting creative differences undermined the partnership. Gates distributed an internal memo on May 16, 1991, announcing that the OS/2 partnership was over and Microsoft would shift its efforts to the
development.
Gates began to realize the expectations others had of him when public opinion mounted that he could give more of his wealth to charity. Gates studied the work of
and
and in 1994 sold some of his Microsoft stock to create the
William H. Gates Foundation. In 2000, Gates and his wife combined three family foundations into one to create the charitable
, which is the largest transparently operated charitable foundation in the world.

Gates has authored two books:


(1995)
(1999).
Herman Hollerith was an American statistician who developed a mechanical tabulator based on punched cards to rapidly tabulate statistics from millions of pieces of data. He was the founder of one of the companies that later merged and became IBM .
Electronic tabulation of data:
Hollerith tabulating machine and sorter
At the urging of John Shaw Billings , Hollerith developed a mechanism using electrical connections to trigger a counter, recording information. A key idea was that data could be coded numerically.
Hollerith saw that if numbers could be punched in specified locations on a card, in the now familiar rows and columns, then the cards could be counted or sorted mechanically and the data recorded. A description of this system, An Electric Tabulating System (1889) , was submitted by Hollerith to
Columbia University as his doctoral thesis, and is reprinted in Randell's book.On January 8, 1889,
Hollerith was issued U.S. Patent 395,782,claim 2 of which reads:
The herein-described method of compiling statistics, which consists in recording separate statistical items pertaining to the individual by holes or combinations of holes punched in sheets of electrically non-conducting material, and bearing a specific relation to each other and to a standard, and then counting or tallying such statistical items separately or in combination by means of mechanical counters operated by electro-magnets the circuits through which are controlled by the perforated sheets, substantially as and for the purpose set forth.
Inventions and businesses:
Hollerith punched card

Hollerith had left teaching and begun working for the United States Census Office in the year he filed his first patent application. Titled "Art of Compiling Statistics", it was filed on September 23, 1884;
U.S. Patent 395,782 was granted on January 8, 1889.
Hollerith built machines under contract for the Census Office, which used them to tabulate the 1890 census in only one year. The 1880 census had taken eight years. Hollerith then started his own business in 1896, founding the Tabulating Machine Company . To make his system work, he invented the first automatic card-feed mechanism and the first key punch (that is, a punch operated by a keyboard ); a skilled operator could punch 200 –300 cards per hour. He also invented a tabulator .
The 1890 Tabulator was hardwired to operate only on 1890 Census cards. A control panel in his 1906
Type I Tabulator allowed it to do different jobs without being rebuilt (the first step towards programming). These inventions were among the foundations of the modern information processing industry.
In 1911 four corporations, including Hollerith's firm, merged to form the Computing Tabulating
Recording Corporation (CTR).Under the presidency of
, it was renamed International
Business Machines Corporation (IBM) in 1924.
George Boole was an English mathematician and philosopher .
As the inventor of Boolean logic —the basis of modern digital computer logic —Boole is regarded in hindsight as a founder of the field of computer science . Boole said,
... no general method for the solution of questions in the theory of probabilities can be established which does not explicitly recognize ... those universal laws of thought which are the basis of all reasoning ...
Work:
His earliest published paper was the "Researches in the theory of analytical transformations, with a special application to the reduction of the general equation of the second order." A long list of Boole's memoirs and detached papers, both on logical and mathematical topics, are found in the Catalogue of
Scientific Memoirs published by the Royal Society , and in the supplementary volume on Differential
Equations , edited by Isaac Todhunter . To the Cambridge Mathematical Journal and its successor, the Cambridge and Dublin Mathematical Journal , Boole contributed twenty-two articles in all. In the third and fourth series of the Philosophical Magazine are found sixteen papers. The Royal Society printed six

important memoirs in the Philosophical Transactions , and a few other memoirs are to be found in the Transactions of the Royal Society of Edinburgh and of the Royal Irish Academy , in the Bulletin de l'Académie de St-Pétersbourg for 1862, and in Crelle's Journal . Also included is a paper on the mathematical basis of logic, published in the Mechanic's Magazine in 1848. The works of Boole are thus contained in about fifty scattered articles and a few separate publications.
Detail of stained glass window in Lincoln Cathedral dedicated to George Boole
Only two systematic treatises on mathematical subjects were completed by Boole during his lifetime.
The well-known Treatise on Differential Equations appeared in 1859, and was followed, the next year, by a Treatise on the Calculus of Finite Differences , designed to serve as a sequel to the former work.
His principal characteristic was perfect confidence in any result obtained by the treatment of symbols in accordance with their primary laws and conditions, and an almost unrivaled skill and power in tracing out these results.
With the exception of Augustus De Morgan , Boole was probably the first English mathematician since the time of John Wallis who had also written upon
. Boole afterward regarded this as a hasty and imperfect exposition of his logical system, and he desired that his much larger work, An Investigation of the Laws of Thought (1854), on Which are Founded the Mathematical Theories of Logic and
Probabilities , should alone be considered as containing a mature statement of his views.
Plaque beneath Boole's window in Lincoln Cathedral
He did not regard logic as a branch of mathematics, as the title of his earlier pamphlet might be taken to imply, but he pointed out such a deep
the symbols of algebra and those that can be made, in his opinion, to represent logical forms and syllogisms , that we can hardly help saying that formal logic is mathematics restricted to the two quantities, 0 and 1. By unity Boole denoted the universe of thinkable objects;
, such as x , y , z , v , u , etc., were used with the elective meaning attaching to common adjectives and substantives. Thus, if x = horned and y = sheep, then the successive acts of election represented by x and y , if performed on unity, give the whole of the class horned sheep. Boole showed that elective symbols of this kind obey the same primary laws of combination as algebraic symbols, whence it followed that they could be added, subtracted, multiplied and even divided, almost exactly in the same manner as numbers. Thus, (1 – x ) would represent the operation of selecting all things in the world except horned things, that is, all not horned things, and (1 – x ) (1 – y ) would give us all things neither horned nor sheep. By the use of such

symbols propositions could be reduced to the form of equations , and the syllogistic conclusion from two premises was obtained by eliminating the middle term according to ordinary algebraic rules.
Charles Babbage was born in London Dec. 26, 1791, St. Stephan day, in
London.
 Difference engine:
Babbage presented something that he called "difference engine" to the
Royal Astronomical Society on Jun 14, 1822 and in a paper entitled "Note on the application of machinery to the computation of astronomical and mathematical tables."
It was able to calculate polynomials by using a numerical method called the differences

 method.
Charles wrote, "The drawings and parts of the Engine are at length in a place of safety —
I am almost worn out with disgust and annoyance at the whole affair." In 1842 the government officially abandoned the project.
Between 1833 and 1842 he tried to build a machine that would be programmable to do any kind of calculation, not just ones relating to polynomial equations. The first breakthrough came when he redirected the machine's output to the input for further equations. He described this as the machine "eating its own tail". It did not take much longer for him to define the main points of his analytical engine.
The mature analytical engine used punched cards adapted from the Jacquard loom to specify input and the calculations to perform. The engine consisted of two parts: the mill and the store. The mill, analogous to a modern computer's CPU, executed the operations on values retrieved from the store, which we would consider memory. It was the world's first general-purpose computer.
A design for this emerged by 1835. Babbage and a handful of assistants created 500 large design drawings, 1000 sheets of mechanical notation, and 7000 sheets of scribbles. The completed mill would measure 15 feet tall and 6 feet in diameter. The 100 digit store would stretch to 25 feet long. Babbage constructed only small test parts for his new engine; a full engine was never completed.

Between October 1846 and March 1849 Babbage started designing a second difference engine using knowledge gained from the analytical engine. It used only about 8000 parts, three times fewer than the first. It was a marvel of mechanical engineering.
Unlike the analytical engine that he continually tweaked and modified, he did not try to improve the second difference engine after completing the initial design. Babbage made no attempt to actually construct the machine.
The 24 schematics remained in the Science Museum archives until a full-size replica was built 19851991 to celebrate the 200th anniversary of Babbage’s birth. It measured 11 feet long, 7 feet high and 18 inches deep, and weighted 2.6 tonnes. The limits of precision were restricted to those achievable by Babbage.