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

2 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

3 AT and ATX IBM Intel The motherboard is an integral part in a computer since it is where all the components are attached to. ԬThere 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 IBM 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. Intel 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.

4 The ATX specification was set forth publicly by Intel Corp. in 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 Cont..

5 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 AT and ATX Cont..

6 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.

7 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.

8 AT /ATX Summary: 1. AT is an old standard that has been totally replaced by ATX 2. AT boards are wider compared to ATX by almost 4 inches 3. ATX allows board makers to customize the ports in the back with backplates which is not possible with AT 4. AT computers had their power switches connected directly to the power supply while in ATX systems, the switch is connected to the motherboard

9 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 , while the ATX standard is current.

10 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

11 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

12 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

13 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

14 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 ATX

15 Power supply CD-ROM drive Floppy disk drive Hard disk drive Wires and ribbon cables Sound/network cards 1. Inside a PC Mother board

16 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

17 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

18 Random Access Memory (RAM) chips. Expansion slots Motherboard Picture Read-only Memory (ROM) chips Processor chip (the CPU)

19 A data bus (a data path): connects the parts of the motherboard. Moving Data RAM via expansion cards

20 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

21 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.

22 Each RAM location has an address and holds one byte of data (eight bits). RAM Storage

23 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?

24 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

25 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

26 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

27 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 motherboard components  CPU examples: the Pentium, the PowerPC chip The CPU is also known as the processor or microprocessor.

28 Some Processors (CPUs) PowerPC Chip Chip Fan Pentium Chip

29 The CPU and RAM The CPU processes data. The RAM contains data and programs. The data bus transports the processed data to the RAM so it can be stored, displayed, or output.

30 The CPU in Action The CPU

31 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

32 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.

33 The CPU executes a series of instructions by looping through an instruction cycle. The CPU Instruction Cycle The speed of the instruction cycle is controlled by the CPU's clock.

34 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

35 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

36 The expansion bus transports data through the motherboard. Most expansion cards contain a port. A connector cable plugs into the port, and leads to a peripheral. 7. Expansion Slots Data originates in RAM Expansion slot containing an expansion card. continued

37 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.

38 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

39 Connector Cables continued

40

41 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 an example of computer booting.

42 The computer checks the CMOS memory. The computer loads configuration settings from Config.sys or the Windows Registry. Other Booting Tasks

43 If nothing happens, the system is not getting power. When you turn on a computer, you should see the power light and hear the fan. Common Problems #1 Fan Power light

44 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

45 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

46 Configuration data is missing or corrupted  in the CMOS or the Windows Registry This will generate on-screen messages. Common Problems #4

47 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

48 Windows Safe Mode Picture

49 B.A. (Mahayana Studies) Introduction to Computer Science November March 2006 REFERENCES 00_types-atx-motherboards.html