Module 2
How Computers Work
Basic Functions of an Operating Systems
• Input – recognizing input from the keyboard or mouse
• Processing –- manipulating data according to the user's
instructions
• Output – sending output to the video screen or printer
• Storage – keeping track of files for use later; examples of
storage devices include floppy disks and hard drives.
Bootstrap
• For an operating system to run, it must be loaded into the
computer's Random Access Memory (RAM).
• When a computer is first turned on, it launches a small program
called the bootstrap loader that is located on the BIOS chip
on the motherboard.
• The bootstrap's primary functions are to test the computer's
hardware and to locate and load the operating system into
RAM.
Power-On Self Test
• To test the computer's hardware, the bootstrap program runs a program
called power-on self-test or POST.
• In this test, the computer's Central Processing Unit (CPU) checks itself
first and then checks the computer's system timer.
• The POST checks the Random Access Memory (RAM) by writing data to
each RAM chip and then reading that data. Any difference indicates a
problem.
• If the POST finds errors, it sends a message to the computer monitor. If
the POST finds errors that cannot be displayed on the monitor, it sends
errors in the form of "beeps."
• The POST sends one beep and the screen begins to display OS loading
messages once the bootstrap has determined that the computer has
passed the POST.
Generic Cold Boot Sequence
Desktop / Tower Models
Tower Models
Power
Floppy disk drive
CD-ROM drive
Hard disk drive
LEDs
NIC
Video card
Audio card
Parallel port
Serial port
Mouse Port
Power Supplies




Converts AC to DC
Typically 250 –300 watts
AT
 P8 & P9 connector
 12 pin
 +5, -5, +12, -12
ATX
 P1 connector
 20 pin (keyed)
 +3.3,+5, -5, +12, -12
Cooling Systems



The power supply fan helps
prevent the computer
components from
overheating by maintaining
airflow in the case.
Overheating is a critical
problem that can cause a
computer system to
malfunction or fail.
A heat sink is made of a
material that absorbs the
heat generated.
Motherboards
• System board / main board is crucial because it is the nerve
center of the computer system. Everything else in the system
plugs into it, is controlled by it, and depends on it to
communicate with other devices on the system.
• It generally houses the CPU, the controller circuitry, the bus,
RAM, expansion slots for additional boards, and ports for
external devices. In addition, it contains the CMOS and other
ROM BIOS and support chips providing varied functionality.
Motherboard Form Factors
• Describe their physical dimensions.
• AT
• ATX
• The ATX motherboard is similar to the Baby AT
motherboard, except for a number of important
enhancements. Most new systems come with the ATX
motherboard form factor.
Motherboard Components
• The major components on the motherboard include:
• chipset – interconnects all the devices on the motherboard
• CPU socket
• expansion sockets
• I/O support
• BIOS
• RAM sockets
• power supply socket
• CMOS chip
• dip switches and jumpers
• memory cache
The Motherboard
The Motherboard
The Motherboard
The Motherboard
Inside the Computer
Power
Supply
Hard (C)
Drive
Floppy (A)
Drive
CD (D)
Drive
Sound Card
Video Card
Back Plane Card
Motherboard
RAM
Processor
Speaker
ISA slot
joystick
connector
printer
connector
USB ports
AMR slot
Mouse and
keyboard
connector
processor
(ZIF)
socket
AGP slot
chipset
power
connector
PCI slots
IDE
connectors
hard
drive
CD
Drive
Floppy
connector
DIMM memory
slots
ISA slot
Expansion Slots
AMR slot
AGP slot
PCI slots
ISA – Industry Standard Architecture
AMR – Audio/Modem Riser
AGP – Accelerated Graphics Port
PCI – Peripheral Component Interconnect
power
connector
Dual Processor Motherboard
Floppy
connector
IDE
connectors
hard
drive
DIMM memory slot
CD
Drive
SIMM memory slots
processor
(ZIF)
socket
keyboard
connector
PCI
slot
PC
bus
slots
system
board
IC
ISA
slots
VESA slot
COM 1
COM 2
parallel port PRT 1
system RAM
Floppy
connector
IDE
connectors
System
board IC
power
connector
hard
drive
CD
Drive
Expansion slots
PS/2 or
Mini-Din
ISA slot
mouse
keyboard
USB
Com 1
speaker
Com 2
parallel port/PRT 1
AMR slot
mic
line-in
game port
AGP slot
PCI slots
USB
1/8” Stereo Phone Jacks
RJ-45
DB-15 – Serial Port
DB-9 – Com 1 and Com 2
PS/2 - Mini Din – Keyboard
and Mouse
DB-15 – Video Port
Central Processing Units
Central Processing Unit
• Most important elements of the personal computer.
• On the motherboard, the CPU is contained on
a single integrated circuit called the microprocessor.
• The computer will not run without a CPU.
• Often referred to as the brains of a computer, the CPU contains
two basic components:
• Control unit
• Arithmetic/Logic Unit (ALU)
Control Unit
• Instructs the rest of the computer system on how to follow a
program's instructions.
• It directs the movement of data to and from processor
memory.
• The control unit temporarily holds data, instructions, and
processed information in its arithmetic/logic unit.
• In addition, it directs control signals between the CPU and
external devices such as hard disks, main memory, I/O ports,
etc.
Processor Speed
• CPU descriptions as Pentium 133, Pentium 166, or Pentium 200 are
well known. These numbers are specifications that indicate the
maximum (reliable) operating speed at which the CPU can execute
instructions.
• The CPU speed is not controlled by the microprocessor itself, but by
an external clock located on the motherboard.
• The speed of the processor is determined by the frequency of the
clock signal. Typically expressed in megahertz (MHz), and the higher
the number, the faster the processor.
BIOS ROM
• The basic input/output
system (BIOS) contains
the instructions and data
in the ROM chip that
control the boot process
and the computer
hardware.
• BIOS is sometimes called
firmware.
• The ROM chip that
contains the firmware is
called the ROM BIOS
chip, ROM BIOS, or
simply BIOS.
Expansion Cards
Video card
Modem card
Sound card
Network card
A
G
P
Expansion Slots
• Sockets, are receptacles on the computer motherboard that accept
printed circuit boards. They allow additional devices to be added.
• Examples include video cards, I/O cards, and
sound cards.
• Common expansion slots:
• Industry Standard Architecture (ISA ) – 8 MHz, 16-bit
• Peripheral Component Interconnect (PCI ) – 33 MHz, 32 and 64bit
• Accelerated Graphics Port (AGP) - video adapters – 32-bit
Riser Cards
AMR
Riser card
CNR
Riser Cards
System Buses
RAM – Random Access Memory (SIMMS /
DIMMS / RIMMS)
RAM – Random Access Memory (SIMMS /
DIMMS Installation)
Cache Memory
• L1 cache is located on the CPU.
• L2 cache is located between the
CPU and DRAM.
• L1 cache is faster than L2 because
it is located within the CPU and
runs at same speed as the CPU.
• It is the first place the CPU looks for
its data.
• If data is not found in L1 cache, the
search will then continue with L2
cache, and then on to main
memory.
• COASt modules are used to
provide cache memory on many
Pentium-based systems.
Monitors
• Computers are usually connected to a display, also called a
monitor.
• Some key monitor-related terms are: pixels, refresh rate,
resolution, and size. Measure screen size diagonally.
• Pixels – Are picture elements. The screen image is made of pixels
(tiny dots), which are arranged in rows across the screen. Each
pixel consists of three colors: red, green, and blue (RGB).
• Dot pitch – A measurement of how close together the phosphor
dots are on the screen. The finer the dot pitch, the better image
quality (measured in millimeters).
Display Technology
• CRT – Cathode Ray tube
• LDC – Liquid Crystal Display
• Cable technology - VGA and DVI are the two most
common.
• Viewable area (usually measured diagonally)
• Aspect ratio and orientation (landscape or portrait)
• Maximum resolution
• Dot pitch - Refresh rate - Color depth
• Amount of power consumption
Dot Pitch
Refresh Rate, Measured in Hertz (Hz)
Changing Your Screen Resolution
CRT
A cathode-ray tube is a special-purpose
electron tube in which electrons are
accelerated by high-voltage anodes,
formed into a beam by focusing
electrodes, and projected toward a
phosphorescent screen that forms one
face of the tube. The beam of electrons
leaves a bright spot wherever it strikes the
phosphor screen.
Video Card
video BIOS
video
RAM
video controller
IC
Ports
C
O
M
P
o
r
t
s
USB
DB9
SCSI
Firewire
Mini-DIN
Game Port-DB15
PORTS
DB25--parallel
I /O Ports
• All peripheral devices that connect to the computer such as printers,
scanners, and so on, use connectors on the back of the computer
known as ports.
• Ports:
• Serial ports – 1 bit at a time (9 pin male)
• Parallel ports – 1 byte at a time
• USB (Universal serial bus) – 127 devices daisy chained, hot
swappable, 450 Mbps
• Modem - RJ11 connectors
• NIC – RJ45 connectors
• Firewire – 63 devices using cable lengths up to 4.5 m, 400Mbps
Serial Ports
• A serial port can be used to connect devices that use a serial
interface such as a modem, scanner, mouse, etc.
• Generally, a PC can identify up to four serial ports, but the
typical computer contains only two, referred to as COM1 and
COM2.
• A serial port transmits data bits one after the other (serially)
over a single line.
Parallel Ports
• A parallel port is a socket on the computer that is used to
connect a printer or other peripheral device such as a portable
hard disk, tape backup, scanner, or a CD-ROM.
• The parallel port contains eight lines for transmitting an entire
byte (8 bits) across the eight data lines simultaneously.
• Parallel ports can be configured as
• LPT1 (IRQ 7)
• LPT2 (IRQ 5)
PS/2 Ports
• PS/2 keyboard or PS/2 mouse ports (Mini-DIN) are used to
connect your PC to its keyboard and mouse.
• Both ports look identical, ports are not interchangeable.
• Mouse (green)
• Keyboard (purple).
• Usually both ports are color coded or labeled to avoid any
confusion.
USB – Universal Serial Bus



127 devices
Transfer rate up to 12
Mbps
USB 2.0 up to 450 Mbps
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USB keyboards
Mice
Printers
Modems
Scanners
Digital cameras
Digital video cameras
External disk drives
EIDE and SCSI Controllers
• The internal hard drive is connected to a disk controller with a
cable—a 40 pin cable.
• The hard drive and other devices can use one of two types of
interface controllers to work with the computer.
• These include the Enhanced Integrated Drive Electronics
(EIDE), and Small Computer System Interface (SCSI,
pronounced "scuzzy") connections.
EIDE Controllers
• Enhanced IDE (EIDE) is the "new and improved" Integrated
Drive Electronics (IDE) drive interface.
• Not confined to IDE's 528 MB of data, the EIDE interface can
handle up to 8.4 GB or more.
• While IDE can support only two drives, EIDE can support up to
four devices using two IDE cables.
SCSI Controllers
Small Computer System Interface
• Like EIDE, SCSI devices have the controlling electronics on each of
the drives.
• A standard SCSI interface will allow up to 7devices to be connected
to one SCSI adapter or controller. If the SCSI card is counted, it
makes eight SCSI devices.
• Such devices may include hard drives, CD-ROM drives, taped drives,
scanners, and removable drives.
• Each SCSI device in the chain, including the SCSI controller card is
given a SCSI ID number from 0 to 7; #0 for the primary boot device
(hard drive), and #7 for the SCSI controller card.
SCSI continued . .
Hard Disk Drive
• The HDD has a much larger storage capacity than the floppy
for long-term storage.
• It stores your programs and files, as well as the operating
system.
• Typically, the HDD is an internal drive that cannot be
removed from the computer.
Hard Disk Drive Components
• Disk platters, read/write heads, head actuator
assembly, spindle motor, logic/circuit board,
bezel/faceplate, configuration jumpers, and interface
connectors.
• Disk platters are the actual media on which data is
stored in the hard disk drive.
• Read/write heads are used to access the media.
The disk platters require a read/write head for each
side.
• Spindle motor which spins the platters.
Floppy Disk Drive



3.5”
1.44 MB storage
Write Protect
CD ROM

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
Secondary Storage Device
CD-ROM Speed indicated by x
(multiples of 150 kbps)
 CR-ROM – Read Only
 CD-R – Record able
 CD-RW – Record able &
rewrites
650 – 700 MB
52x/32x/52x
W /RW/R
DVD – Digital Video Disk



Storage Capacity 25 times
more than CDs
DVD-R
DVD-RW
NIC –Network Adapter Card

Network Interface



Token Ring
Ethernet
RJ-45
Modem
 uses
Dial Up Network
connection
 converts digital data into
analog
 modulates/demodulates
 56 Kbps
 RJ-11 connectors
 UART chip—16550
 V.92 current standard
Interrupt Request
“Hey CPU wake up and process this.”
• Modern computers and operating systems owe their reliability
to the organized way in which they handle internal
transactions.
• Various hardware devices, for example, may want to tell the
CPU that they have some information available that is ready for
transfer.
• The devices indicate this by making an interrupt request, or
IRQ.
• It is a general rule that IRQs CANNOT be shared.
Interrupt Request
Direct Memory Access (DMA)
• Channels allow devices to bypass the processor and directly
access the computer memory.
• Devices with a DMA channel assignment, as a result, gain the
advantage of faster data transfers.
• DMA channels are typically used by high-speed communication
devices for transferring large amounts of data at high speeds.
• Examples of such devices include sound cards, some network
cards, some SCSI cards, some disk drives, and some tape
backup drives.
DMA Channels
I /O Address
• In addition to an IRQ, computer components also need to be
assigned an I/O port number.
• An I/O port number is a memory address where data is
temporarily stored as it moves in and out of the devices.
• The I/O address is very similar to a post office box.
I /O Address
32-32-32-FF-EE-77-8
Frequently referred to I / O Addresses:
•3F8 = COM1
•2F8 = COM2
•3E8 = COM3
•2E8 = COM4
•378 = LPT1
•278 = LPT2
Laptop Computers / Batteries / LCD Displays
PCMCIA Cards
Personal Computer Memory Card Interface Association

Type I



Type II



3.3 mm
memory
5.0 mm
NIC, modem, etc.
Type III


10.5 mm
Hard drives
Docking Station

Collection of devices:

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


Monitor
AC Power
Network Connection
Keyboard
Mouse
Printer
Wireless Access Points



Allows computer to go
anywhere within a range
Wired controller receives
and transmits data to
wireless adapter
802.x



A
B
G
Let’s see what you have learned . .
Q:
A:
Q:
A:
Q:
A:
Q:
A:
Q:
A:
Q:
A:
.
How many devices will SCSI 1 support?
7 devices
How many devices will SCSI 2 support?
16 devices
How can I measure a monitor and what are the colors
associated with a monitor?
Diagonally, Red-Green-Blue
What is a warm boot?
Restarting the computer, Ctrl-Alt-Del
What is the very first thing that POST checks?
CPU then memory
Does the external clock on the motherboard determine
the speed of the CPU?
Yes
Q: What type of processor uses Slot A on a
motherboard?
A: AMD
Q: What is AGP?
A: Accelerated Graphics Port, Used for Video adapters
Q: What expansion slot runs at 33 MHz?
A: PCI – Peripheral Component Interconnect
Q: How many pins are there in a SIMM module?
A: 72 pins
Q: How many pins are there in a DIMM module?
A: 168 pins
Q:
A:
Q:
A:
Q:
A:
What type of memory is commonly used as cache?
SRAM – Synchronous Random Access Memory
Is a USB device hot swappable?
Yes
How many devices can I hook up to a USB device?
127