CIM101 : Lecture 04

Organization of a computer

Power Supply Microprocessor

Memory-DRAM- Cache

- ROM BIOS

Keyboard/Mouse

AdapterPort

PrinterPort

Adapter

DisplayPort

Adapter

Hard DiskDrive

Adapter

Floppy DiskDrive

Adapter

Port

Port

Port

Port

System Bus

Expansion Bus Slots

Cards are installed here

Adapters

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The major components of the PC ProcessorI/O devicesMemoryBusAdaptersPortExpansion slotStorage deviceDisplayKeyboardPrinter

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The major components of the PC (Cont.)MousePower supplyCoolingFDDHDDCD-ROM drives

Bus

They connect CPU to each of the memory and

I/O devices.

A collection of wires that act as paths between

the components of a computer.

Example To read/write data from/to memory, a bus is needed.

Types of buses

Three buses:Address bus

Data bus

Control bus

Address busCollection of parallel wires.

Unidirectional, information flows over it only in one direction.

The number of wires indicate the maximum number of memory

addresses. E.g. 20 wires mean 2^20 = 1MB memory.

CPU uses this to address memory and other I/O devices.

Before accessing a particular location in memory or a particular I/O

device, the CPU places the address of that in the address bus.

The address is decoded to select the particular location or device.

Data busBidirectional.

Used for read/write.

Can be either input or output depending on whether the CPU perform a READ or WRITE operation.

The number of wires determines the speed at which data can be read/written.

To read, 1st address is sent using the address bus to enable the desired memory location or I/O device and then memory or the I/O device places the data on the data bus which is read by the CPU.

To write, 1st address is sent using the address bus to enable the desired memory location or I/O device and CPU places data on the data bus which is received by the selected memory or I/O device.

Control bus

A set of signals that is used to control the activities of different

components of the computer in a smooth way.

Some are sent by CPU to other components to tell them the

type of operation in progress.

Also I/O device sends control signal to CPU to indicate its

status.

Example

Read/Write, Reset, Interrupt etc.

Figure of Microprocessor Local Buses

Microprocessor(CPU)

Address Bus

Data Bus

Control Bus

System bus

The 3 buses together are called the system bus

and are guided in parallel to the bus slots.

Several bus architectures used in

microcomputers are:AT, ISA, EISA, IBM etc.

The PCI BUS It stands for peripheral component interconnect.

Introduced by Intel.

Defines a local bus that allows up to ten PCI complaint expansion cards to be plugged into the computer.

One of these ten cards must be the PCI controller card and others are video card, network interface card etc.

PCI controller exchanges information with the computer’s processor as 32-bit or 64-bit words and allows PCI adapters to perform certain tasks concurrently with the main processor.

PCI can operate at a bus speed of 32MHz.

AdaptersAllow processor to communicate with and control

I/O or storage devices.A set of hardware circuitry.Connects to system bus.Acts as an interface/bridge.Example: serial port adapter, connects to system

bus, and has a port where a modem could be attached.

PortPorts of adapters support attachment of I/O

devices.Expansion slots

Physical connectors.Can be used to attach extra adapters to allow

support of various types of I/O devices.Storage devices

Hard disks and CD-ROMS.Display

Most common CRT For laptops, LCD. Needs the display adapter to attach the monitor.

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KeyboardHas an 8-bit processor inside.Used to detect key presses/releases.The adapter itself has an 8-bit processor

that gets keystroke reports from the keyboard processor.

PrinterAttached to parallel port. 8 bits data transfer at a time.Keyboard- serial mode transfer, bit-by-bit.Parallel port adapter is normally integrated

into the computer motherboard.3 popular printers: dot-matrix, laser, ink jet.

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MousePreferred input device.Used to be connected through serial port.Now has dedicated PS/2 and USB mouse

port.Other ports and adapters

Most computers have 2 serial ports today : COM1 and COM2

Has data rate 115 kbps.Can be of 9 or 25 pins.

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Power supplyConverts standard 220v AC to DC for all the

components of the computer. +5v, -5v, +12v and –12v.

Sometimes supplies AC voltage directly to monitor.

CoolingA fan – to keep the power supply cool.CPU also has a separate cooling fan.Large and powerful computers may need

cooling for each individual adapters and the motherboard.

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Floppy disk drives (FDD)Needed to support floppy disks.Floppy is a magnetic storage medium.Now floppy size = 3.5” in diameter and stores

1.44MB of data.PCs today have FDD adapter built-in.

Hard disk drives (HDD)They attach to computer through IDE

(intelligent drive electronics) adapter port.CD-ROM drives

Can store 700MB of data. 5” in size.They attach to computer through IDE

(intelligent drive electronics) adapter port.

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Real-time clock and calendarIt’s a chip.Has small nonvolatile memory (64 bytes).Power supplied by a small battery.This chip supplies date & time and stores

basic system configuration.Loss of this information destroys system

configuration.

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