Organization of a computer:The motherboard and its

components

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

The major components of the PC • Processor• I/O devices• Memory• Bus• Adapters

– Allow 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.

• Port– Ports 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.

– Picture quality much better than a TV because of higher refresh rate (frames per second) to avoid flicker.

– Higher resolution. E.g. 1024 x 768 pixels. Pixels are the smallest element that can be displayed.

– Needs the display adapter to attach the monitor.

• Keyboard– Has 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.

• Printer– Attached to parallel port. 8 bits data transfer at

a time.– Keyboard- serial mode transfer, bit-by-bit.– Sometimes called Centronics printer port.– Parallel port adapter is normally integrated into

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

• Mouse– Preferred input device.– Used to be connected through serial port.– Now has dedicated PS/2 mouse port.

• Other ports and adapters– Most computers have 2 serial ports today.

Called COM ports.– Has data rate 115 kbps.– Can be of 9 or 25 pins.– Uses the RS-232-C standard.– COM ports are controlled by UART chip

integrated into the motherboard.– Used to be on separate adapter board.

• Power supply– Converts standard 220v AC to DC for all the

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

– Sometimes supplies AC voltage directly to monitor.

• Cooling– A 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.

• Floppy disk drives (FDD)– Needed to support floppy disks.– Floppy is a magnetic storage medium.– Early floppy size = 5.25” in diameter and stored 160KB

of data.– 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.– Suitable for distributing large software.– They attach to computer through IDE (intelligent drive

electronics) adapter port.

The motherboard• Main printed circuit of the computer.• CPU, RAM, ROM, expansion slots, device

controllers are mounted on it.• It’s the heart. All components, features and other

devices are interconnected through it.• Its main components are:

– CPU and upgrade socket.

– Cache and DRAM controller.• The main memory (DRAM) is physically packaged on small

circuit boards called SIMM or DIMM.

• DRAM SIMMs are installed in SIMM sockets.

• Now-a-days only DIMM sockets are used.

• For timing, interface and refresh, a DRAM controller is needed between system bus and DRAM.

• PCI bus bridge chip– Converts system/local bus to PCI bus.– Different for different processors.– Now-a-days Core logic chip set includes this.

• keyboard/mouse controller & chip– Normally built-in adapters are called

controllers. Separate boards mounted on expansion slots are called adapters.

• ROM BIOS– Main job is to load the basic OS from OS’s

boot/startup device and perform power on system test.

– Hard disk is the basic OS boot device.– Normal size is about 128KB.

• Real-time clock and calendar– It’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.

• PCI to ISA bridge– Used for compatibility with old ISA bus.