COMPUTER ARCHITECTURE
Computer Architecture
The actual design and layout of electronic circuits and memory chips, which differences from machine to
machine. In other words, what the computer uses for power and how the computer physically represents,
processes, stores, and moves data. Examples of these are x86, DEC, Motorola 68000.
Integrated Circuits: it is a thin slice of silicon crystal packed with microscopic circuit elements such as wires,
transistors, capacitors, and resistors. They are commonly called chips or microchips.
Motherboard
it is the main circuit board of the computer. It contains the microprocessor, cache chips, the computer
memory, disk drives controllers and other components. Some components are soldered to the board and
some of them can be plugged in to the board and be removed as well.
Numeric data
consists of numbers that represent quantities that might be used in arithmetic operations (it has to be changed
to a binary number).
Character data
is composed of letters, symbols, and numerals that will not be used in arithmetic operations.
Digital computer typically represent character data using codes such as:
ASCII
stands for American Standard Code for Information Interchange. It is a coding scheme to represent
alphabet, numbers and other characters found on a typewriter keyboard as a series of bits. It uses 7 bits to
represent data. Allows:
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Different codes for the letters of our alphabet (uppercase and lowercase)
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Different codes for decimal numbers
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Different codes for mathematical operators and for other special purpose signs ($ % @)
Extended ASCII
uses an additional eighth bit. In addition to what regular ASCII allows, it also:
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Includes the common accents for Spanish, German and French.
EBCDIC
stands for Extended Binary Coded Decimal Interchange Code. It is older than ASCII and represents a
character with 8 bits (28 = 256 bits). Allows:
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Coding of all the Western Languages
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Includes classical Greek
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Includes symbols needed in the arts, sciences and business.
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Does not have enough codes for Chinese or Japanese
Unicode: it uses 16 bits, instead of 8, to code a character, allowing 65,536 different binary codes. With
Unicode, now Chinese, Japanese, and Korean characters are included along with the Roman alphabet,
Cyrillic, and Arabic.
RAM
stands for Random-Access Memory. It is an area in the computer system unit that temporarily holds data
before and after it is processed. Each memory address space contains 8 capacitors, each one holding one bit
(total 1 byte per address space). Its main characteristics are:
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Semiconductor memories made of silicon
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Can hold two electronic states, conducting and non-conducting, matching the binary states 0 and 1
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Quick access to data
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Inexpensive price
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Small physical size for large storage capacity
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Reliability
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Temporary storage of data
ROM stands for Read-Only Memory.
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Bytes of ROM memory can be read out, but they cannot be written over
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Control programs are stored in ROM chips
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The instructions in ROM are permanent, and the only way to change them is to remove the ROM
chips
CMOS memory
stands form complementary metal oxide semiconductor. It holds data, but requires very little power to
retain its contents. It is used to retain vital data about your computer system’s configuration, even when the
computer is turned off. Thus, when your system configuration changes, the data in the CMOS memory must
be updated.
Virtual memory
it is the computer’s ability to use disk storage to simulate RAM. If you don’t have enough RAM to run an
application, this type of memory is used.
CPU
stands for central processing unit. This is the essential core of the computer and is implemented as the
microprocessor. This unit interprets and executes instructions.
ALU
stands for Arithmetic Logic Unit. It is responsible of carrying out mathematical and logical operations inside
the computer’s microprocessor.
CPU instruction
an instruction tells the computer to perform a specific arithmetic, logical, or control operation.
Instruction Cycle
refers to the process in which a computer executes a single instruction. In a nutshell, the steps of an
instruction cycle are: fetch, decode, execute, and increment the instruction pointer.
Word Size : refers to the number of bits that the CPU can manipulate at one time.
Cache Memory
it is a special high-speed memory that gives the CPU more rapid access to data.
CISC
stands for Complex Instruction Set Computer. It contains a complex set of instructions, some of which takes
up more than one clock cycle to execute.
RISC
stands for Reduced Instruction Set Computer. The computer with this type of instruction set has a limited
set of instructions and most of the instructions only require one clock cycle to execute.
Pipelining
it is a technology in which the processor can begin executing an instruction before it completes the previous
instruction.
Parallel processing: refers to a computer that has more than one processor can execute multiple instructions
at the same time. Parallel processing increases the amount of processing that a computer can accomplish in
specific amount of time.
Input/Output
Expansion bus : segment of the data bus that transports data between RAM and peripheral devices.
Expansion card: is a small circuit board that provides a computer with the ability to control a storage, input,
or output device. Also known as expansion boards or controller cards.
Expansion slot
is a long, narrow socket on the motherboard in which you can plug an expansion card. There are three main
types of expansion slots:
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ISA: stands for Industry Standard Architecture. It has the oldest technology of the three and it’s
used today for some modems and other relatively slow devices. Many new computers have few or no
ISA slots.
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PCI: stands for Peripheral Component Interconnect. This type of slot offers fast transfer speeds
and a 64-bit data bus. These slots typically house a graphics card, sound card, video capture card,
modem, or network interface card.
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AGP: stands for Accelerated Graphics Port. It is primarily used for graphics cards and it is faster
than PCI slots. An AGP slot provides a high-speed data pathway that is particularly handy for 3-D
graphics.
Expansion Port
is a connector that passes data in and out of a computer or peripheral device. Ports are also called “jacks” or
“connectors”.