Suleiman Mohammed (mncs,mcpn) Institute of Computing and ICT, Ahmadu Bello

University, Zaria.

A look at the brains of the computer, the motherboard, and its associated components.

THE COMPUTER MOTHERBOARD

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Overview

1. Inside a PC 2. The Motherboard 3. RAM 4. ROM 5. CMOS Memory 6. The CPU 7. Expansion Slots 8. Booting the Computer

types of memory

the 'brains'

the processor

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AT and ATXAT and ATX

The motherboard is an integral part in a computer since it is where all the components are attached to. ‘¨There are many standards for motherboards and the cases that holds them. The most prominent standards are AT and ATX. AT is a very old standard that was created by IBMIBM for their own computers. ATX was developed by Intel to address some of the shortcoming of the AT standard that makes it unsuitable for the varied demands of personal computing.AT boards were much bigger compared to ATX boards. ATX boards were made narrower by almost 4 inches to ensure that there is no overlap.

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The ATX specification was set forth publicly by Intel Corp. in 1995. The ATX specification was released as a successor to the AT specification. The necessity for this action on Intel's part was that the AT form factor was significantly antiquated, and possessed several design flaws when coupled with the modern computer hardware of the time. Though Intel has subsequently released the BTX form factor, it has not taken hold as an industry-standard and as a corollary, the ATX specification continues to be updated and revised.

AT and ATX AT and ATX Cont..Cont..

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ATX form factor is the governing specification concerning the motherboard's dimensions, electrical connectivity and I/O interface placement. The specifications govern acceptable power supplies, cases and the overall maximum size of hardware devices that can be installed on the motherboard. For example, the current ATX specification, revision 2.2, requires a 24 pin power connector, and is 12-by- 9.6 inches in dimension. The design also allows for further spacing between PCI-e interfaces on the motherboard to accommodate larger graphics cards which have come into use as of 2007.

AT and ATX AT and ATX Cont..Cont..

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AT and ATX Cont..AT and ATX Cont..

Another shortcoming of the AT system is in the ports at the back. AT boards only had the most minimal amount connectors in order to maintain compatibility with AT cases. If you like more connectors, you would need to add flying leads to unused expansion slots. ATX cases allowed manufacturers to produce their own custom backplates to suit their motherboards. This allowed most ports to be integrated to the board and moved up, making it much less of an effort to install a new motherboard and even frees up some of the expansion slots taken up by the ports.

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AT and ATX Cont..AT and ATX Cont..

ATX boards also introduced the ‘soft off’ capability. Prior to ATX, the power switch was directly connected to the power supply and the computer cannot turn itself off. ATX cases moved the switch to the motherboard. Computers then had the ability to turn itself on or off depending on its programming. You would no longer need to wait for the computer to safely shutdown before turning it off. It also paved the way for the additional features like WOL (Wake On Lan) that allows computers to be turned on remotely via its network adapter.

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AT /ATX Summary:AT /ATX Summary:

1. AT is an old standard that has been totally replaced by ATX2. AT boards are wider compared to ATX by almost 4 inches3. ATX allows board makers to customize the ports in the back with backplates which is not possible with AT4. AT computers had their power switches connected directly to the power supply while in ATX systems, the switch is connected to the motherboard

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Differences Between AT & ATX Power Supplies

AT (Advanced Technology) and ATX (Advanced Technology Extended) are two incompatible power supply standards. While both power supplies share some of the same connectors, the technology behind both of them is quite different, requiring different motherboards and computer cases. The AT style was used from approximately 1980-1997, while the ATX standard is current.

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The main power connector on AT and ATX power supplies are very different, and require different motherboards because of this. The main power connector on an AT power supply is actually two separate six-pin connectors that plug into the motherboard side by side in a single row. The ATX main power connector is a single 20 or 24-pin connector that places the pins on two rows.

Main Power Connector

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The power switch of AT style power supplies is integrated directly into the power supply itself. This is a physical switch that turns the power supply on and off. ATX style power supplies use a "soft switch" that is controlled by the motherboard. This enables a computer with an ATX power supply to power off via software.

Power Switch

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Older power supplies provide a lower wattage rating than newer ones. Newer ATX style power supplies typically provide 300 or more watts, whereas AT style power supplies typically provide wattage of less than 250.

Wattage

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Though AT and ATX power supplies share many connectors, ATX power supplies may have connectors, such as SATA and 4-pin ATX12V, that never appeared on AT power supplies due to the technology post-dating the AT power supply. Additionally, an AT power supply has more mini-Molex connectors for devices such as floppy drives.

Connectors

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The extended ATX, or eATX, form factor was originally released as a workstation level motherboard specification. The physical dimensions of the motherboard could be 12-by-13 inches. This somewhat dramatic increase in size is due to the fact that enterprise level motherboards are required to house much more internal hardware than consumer level computers. Recently, however, there has been a higher consumer user demand for this form factor as technologies such as NVIDIA's SLI and ATI's Crossfire call for very large motherboards to accommodate two to four graphics cards, each two PCI slots in width.

Extended ATXExtended ATX

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Powersupply

CD-ROM drive

Floppydisk drive

Hard disk drive

Wires andribbon cables

Sound/networkcards

1. Inside a PC

Motherboard

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The most important part of a PC is the motherboard. It holds: the processor chip memory chips chips that handle input/output (I/O) the expansion slots for connecting peripherals

Some chips are soldered onto the motherboard(permanent), and some are removable (so they can be upgraded).

2. The Motherboard

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A chip (microchip) is an integrated circuit - a thin slice of silicon crystal packed with microscopic circuit elements e.g. wires, transistors,

capacitors, resistors

A Chip

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Random AccessMemory (RAM)chips.

Expansion slots

Motherboard Picture

Read-onlyMemory (ROM)chips

Processor chip(the CPU)

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A data bus (a data path): connects the parts of the motherboard.

Moving Data

RAM

via expansion cards

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Random Access Memory (RAM). RAM is used to hold programs while they are

being executed, and data while it is being processed.

RAM is volatile, meaning that information written to RAM will disappear when the computer is turned off.

3. RAM

continued

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RAM contents can be accessed in any (i.e. random) order.

By contrast, a sequential memory device, such as magnetic tape, forces the computer to access data in a fixed order because of the mechanical movement of the tape.

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Each RAM locationhas an address and holds one byte of data (eight bits).

RAM Storage

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Computers typically have between 64 and 512 Mb (megabytes) of RAM.

RAM access speeds can be as fast as 8 nanoseconds (8 billionth of a second).

The right amount of RAM depends on the software you are using.

You can install extra RAM.

How much RAM is Enough?

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Virtual memory uses part of the hard disk to simulate more memory (RAM) than actually exists.

It allows a computer to run more programs at the same time.

Virtual memory is slower than RAM.

Virtual Memory

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Read-Only Memory can be read but not changed.

It is non-volatile storage: it remembers its contents even when the power is turned off.

ROM chips are used to store the instructions a computer needs during start-up, called firmware.

Some kinds of ROM are PROM, EPROM, EEPROM, and CD-ROM.

4. ROM

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A computer needs a semi-permanent way of keeping some start-up data e.g. the current time, the no. of hard disks the data may need to be updated/changed

CMOS memory requires (very little) power to retain its contents. supplied by a battery on the motherboard

5. CMOS Memory

the battery

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6. The CPU

The Central Processing Unit (CPU) is the chip on the motherboard that acts as the "computer's brain" it does calculations, and coordinates the other mothe

rboard components CPU examples: the Pentium, the PowerPC chip

The CPU is also known as the processor or microprocessor.

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Some Processors (CPUs)

PowerPC Chip

Chip Fan

Pentium Chip

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The CPU and RAM

The CPUprocesses data.

The RAMcontains dataand programs.

The data bus transports theprocessed data to the RAM soit can be stored, displayed, oroutput.

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The CPU in Action

The CPU

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The instruction pointer in the CPU's control unit stores the location of the next program instruction to be executed.

The instruction is loaded into the instruction register to be carried out. registers are local memory on the CPU

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The ALU (arithmetic logic unit) executes the instruction.

The result is placed in the accumulator (another register), then stored back in RAM or used in other CPU operations.

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The CPU executes a series of instructions by looping through an instruction cycle.

The CPU Instruction Cycle

The speed of theinstruction cycleis controlled bythe CPU's clock.

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The system clock sends out 'ticks' to control the timing of all the motherboard tasks e.g. it controls the speed of the data bus and the

instruction cycle

The time it takes to complete an instruction cycle is measured in megahertz (MHz). 1 MHz = one million cycles per second

The System Clock

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Word size: the number of bytes the CPU can process at once. depends on the number of registers in the CPU; depends on the size of the data bus

Cache size: the cache is high-speed memory on the CPU that stores data which is needed often.

Two Measures of CPU Size

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The expansion bus transports data through the motherboard.

Most expansion cardscontain a port.

A connector cable plugsinto the port, and leads to a peripheral.

7. Expansion Slots

Data originatesin RAM

Expansion slot containing an expansion card.

continued

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Common expansion cards: graphics card (for connecting to a monitor) network card (for transmitting data over a network) sound card (for connecting to a microphone and

speakers)

Most PCs offer 4-8 expansion slots.

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There are several different types of expansion slot: ISA: older technology, for modems and slow devices PCI: for graphics, sound, video, modem or network

cards AGP: for graphics cards

Expansion Slot Types

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Connector Cables

continued

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Booting is the sequence of computer operations from power-up until the system is ready for use this includes hardware testing, and loading the OS

8. Booting a Computer

This is not anexample ofcomputer booting.

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The computer checks the CMOS memory.

The computer loads configuration settings from Config.sys or the Windows Registry.

Other Booting Tasks

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If nothing happens, the system is not getting power.

When you turn on a computer, you should see the power lightand hear the fan.

Common Problems #1

Fan

Power light

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If the ROM chips, RAM, or processor are broken, then the computer will stop or 'hang' the light and fan will be on, but... there will be no messages on the screen

Common Problems #2

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The Power-On Self-Test (POST) automatically checks for problems in the computer.

POST checks: the graphics card, RAM, the keyboard performs drives test

hard drive, CD drives, floppy drive

Problems are reported by various beeps, or by on-screen messages.

Common Problems #3

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Configuration data is missing or corrupted in the CMOS or the Windows Registry

This will generate on-screen messages.

Common Problems #4

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If MS Windows cannot complete booting, it may start in Safe Mode.

Safe Mode is a limited version of Windows that allows you to use only the mouse, monitor, and keyboards no peripherals the screen icons will probably look very large

Windows Safe Mode

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Windows Safe Mode Picture

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B.A. (Mahayana Studies)000-209 Introduction to Computer ScienceNovember 2005 - March 2006

REFERENCES

http://www.ehow.com/about_5373400_types-atx-motherboards.html