Motherboard

What is a Motherboard' Motherboard is the most important component in any personal computer. It contains almost every important elements of the computer. Sometimes instead of the calling it “motherboard”, IBM refers to is as “system Board” or “ Planner Board” , some other manufacturer refer to this as the “Logic Board”. The motherboard is the main circuit board inside the PC which holds the processor, memory and expansion slots and connects directly or indirectly to every part of the PC. It’s made up of a chipset(known as the “glue logic”), some code in ROM and the various interconnections or buses. Evolution The original PC had a minimum of integrated devices, just ports for a keyboard and a cassette deck (for storage). Everything else, including a display adapter and floppy or hard disk controllers, were add-in components, connected via expansion slots. 1995 - I/O ports and disk controllers were often mounted on expansion cards. Other components - typically graphics, networking, SCSI and sound - usually remain separate. Consequently, those parts of the system whose specification changes fastest - RAM, CPU and graphics - tend to remain in sockets or slots for easy replacement. Similarly, parts that not all users need, such as networking or SCSI, are usually left out of the base specification to keep costs down. The basic changes in motherboard form factors over the years are covered later in this section - the diagrams below provide a detailed look at the various components on two motherboards. The first a Baby AT design, sporting the ubiquitous Socket 7 processor connector, circa 1995. The second is an ATX design, with a Pentium II Slot 1 type processor connector, typical of motherboards on the market in late 1998. Baby AT Design ATX Design Motherboard development consists largely of isolating performance-critical components from slower ones. As higher speed devices become available, they are linked by faster buses -and the lower-speed buses are relegated to supporting roles. In the late 1990s there was also trend towards putting peripherals designed as integrated chips directly onto the motherboard. Initially this was confined to audio and video chips - obviating the need for separate sound or graphics adapter cards - but in time the peripherals integrated in this way became more diverse and included items such as SCSI, LAN and even RAID controllers. While there are cost benefits to this approach the biggest downside is the restriction of future upgrade options. Motherboard Form Factors Early PCs used the AT form factor and 12in wide motherboards. The sheer size of an AT motherboard caused problems for upgrading PCs and did not allow use of the increasingly popular slimline desktop cases. These problems were largely addressed by the smaller version of the full AT form factor, the Baby AT, introduced in 1989. There is several common form factors used for PC motherboards. The form factors refer to the physical dimensions and size of the board, and dictates what type case is motherboard will fit into. The PC motherboard form factors generally available include the following. Baby – AT NLX LPX Backplane systems ATX Proprietary designs BAT(Baby –AT) The Baby AT (BAT) format reduced the dimensions of the motherboard to a typical 9in wide by 10in long, and BAT motherboards are generally characterized by their shape, an AT-style keyboard connector soldered to the board and serial and parallel port connectors which are attached using cables between the physical ports mounted on the system case and corresponding connectors located on the motherboard. With the BAT design the processor socket is located at the front of the motherboard, and full length expansion cards are intended to extend over it. This means that removing the processor requires the removal of some or all expansion cards first. Problems were exacerbated by the increasing speeds of Pentium-class processors. Baby –AT Motherboard System cooling relied on the AT power supply blowing air out of the chassis enclosure and, due to the distance between the power supply and the CPU, an additional chassis fan or active heatsink became a necessity to maintain good airflow across the CPU. AT power supplies only provide 12V and 5V outputs to the motherboard, requiring additional regulators on the motherboard if 3.3V components (PCI cards or CPUs) are used. Sometimes a second heatsink was also required on these voltage regulators and together the various additional heat dissipation components caused serious obstruction for expansion slots. Some BAT designs allow the use of either AT or ATX power supplies, and some ATX cases might allow the use of a Baby-AT motherboard. ATX The Intel Advanced/ML motherboard, launched in 1996, was designed to solve these issues and marked the beginning of a new era in motherboard design. Its size and layout are completely different to the BAT format, following a new scheme known as ATX. The dimensions of a standard ATX board are 12in wide by 9.6in long; the mini ATX variant is typically of the order 11.2in by 8.2in. The ATX design gets round the problem by moving the CPU socket and the voltage regulator to the right-hand side of the expansion bus. Room is made for the CPU by making the card slightly wider, and shrinking or integrating components such as the Flash BIOS, I/O logic and keyboard controller. This means the board need only be half as deep as a full size Baby AT, and there’s no obstruction whatsoever to the six expansion slots (two ISA, one ISA/PCI, three PCI). ATX Motherboard The ATX uses a new specification of power supply that can be powered on or off by a signal from the motherboard. This allows notebook-style power management and software-controlled shutdown and power-up. A 3.3V output is also provided directly from the power supply. Accessibility of the processor and memory modules is improved dramatically, and relocation of the peripheral connectors allows shorter cables to be used. This also helps reduce electromagnetic interference. The ATX power supply has a side vent that blows air from the outside directly across the processor and memory modules, allowing passive heatsinks to be used in most cases, thereby reducing system noise. Mini-ATX is simply a smaller version of a full-sized ATX board. On both designs, parallel, serial, PS/2 keyboard and mouse ports are located on a double-height I/O shield at the rear. Being soldered directly onto the board generally means no need for cable interconnects to the on-board I/O ports. A consequence of this, however, is that the ATX needs a newly designed case, with correctly positioned cut-outs for the ports, and neither ATX no Mini- ATX boards can be used in AT-style cases. NLX Intel’s NLX design, introduced in 1997, is an improvement on the LPX design for low-profile systems, with an emphasis on ease of maintenance. The NLX format is smaller, typically 8.8in wide by 13in long, so well suited for low-profile desktop cases. All expansion slots, power cables and peripheral connectors are located on an edge-mounted riser card, allowing simple removal of the main motherboard, which is mounted on rails in the chassis. It uses a full width I/O shield to allow for different combinations of rear-panel I/O. The design allows for use of an AGP card, but the slot must be on the motherboard, which reduces the ease of maintenance when such a card is implemented. AGP card, but the slot must be on the motherboard, which reduces the ease of maintenance when such a card is implemented. NLX Motherboard Proprietary designs motherboards that are not one of the standard form factors such as Full sized –AT, Baby- AT, ATX or NLX are called as proprietary. Backplane systems: One type of proprietary design is the backplane system. These systems do not have a motherboard, the components normally found on the motherboard are located on an expansion adapter card plugged into a slot. In these systems, the board with the slots is called a backplane rather than a motherboard. Systems using this type of constructions are called backplane systems. Motherboard components A conventional motherboard comprises of various components such as * Expansion slots * CPU(Main Processor) * Coprocessor * Memory * BIOS and * Support circuits of chipset for interrupt, DMA etc. Expansion Slots The expansion slots are long thin connectors on the motherboard, near the backside of the computer. Various expansion cards are connected to the motherboards through data, address and control lines/buses on these slots. Bus is an electronic path on which signals are sent from one part of the computer to another. These buses are categorizes according to the number of BINARY DIGITS (bits) that they can transfer at a time. * If the data bus is 8 bit wide then it can transfer 8 bits of information at a time and called an 8 bit bus. * On a 8 bit data bus transferring 16 bit data requires two data transfers Another very common term while talking about bus is, its “ bandwidth”. The bandwidth of a bus is the measure of data that can fit in the bus at a given time. You can increase the data movement through a bus either by increasing the bus width( from 8 bit to 16 bit) of by increasing the bus bandwidth (8 Mhz to 20 Mhz). Data Bus : Is a set of wires or tracks on the motherboard. Data bus is used to transfer data from one part of the computer to another part. Address Bus : is a set of wires or tracks on the motherboard Printed Circuit Board(PCB) which is used to specify address of a memory location depending on the width and the technology, the expansion slot bus can be divided into the following categories. 8 bit ISA 16 bit ISA MCA EISA VESA local bus or VL bus PCI local Bus CPU (Main Processor) The main component of any motherboard is the main processor chip which controls all the inner functions of the system. The CENTRAL PROCESSING UNIT(CPU) functions as the brain of every PC. It is usually inserted into the socket and is not soldered onto the motherboard as many other chips are normally done, this makes its replacement, in case of any problem, very easy. Some of the common CPU chips are inter 8088,8086,80286,80386,80486, Pentium, Pentium MMX, Pentium –II, Pentium III, Pentium – IV etc. Coprocessor What is a coprocessor' Coprocessor is a special purpose microprocessor, which is used to spped up main processor job by taking over some of the main processors work. Most common type of coprocessor is a math coprocessor. Coprocessor chips are used to help the main processor in carrying out its various functions. A math coproessor helps main processor in performing mathematical calculations Older system (XT, AT, AT-386) required a coprocessor chips to be inserted into special socket on the motherboard, but the current feneration of CPU’s have math coprocessor built inside the main processor itself. Memory What is a memory' Memory is the place where computer stores the program(set of instructions telling ehe computer what to do), and data that help the program in carrying out its operations. For example, a marks sheet printing program will require students rollnumber, name and marks obtained in various subjects etc. as data. There is basically two type of memory used in a computer which are discussed in the previous chapter. RAM memory ROM memory RAM memory RAM or random access memory is a read/write type of memory which is used by the processor to keep program, data and intermediate results during program executions. It is VOLATILE type of memory, which lose ists content when the power supply to it is switched off. The physical installation of RAM memory on the motherboard can take place in various ways. DIP(dual In-line Pin) memory chips were used on initial motherboards. Later SIMM ( single inline memory modules) became common. Currently DIMM(dual inline memory modules) are most common memory module. Bit is a binary digit that is either 0 or 1. Nibble is collection of 4 bits. Byte is collection of 8 bits. Kilobyte is 1024 bytes Megabyte is 1024 Kilobytes Gigabyte is 1024 Megabytes Read Only Memory(ROM) ROM or Read Only Memory, as its name suggest is a read only type of memory it cannot be written. Data is written into it by the manufacturer. On major advantage with the ROM is, ROM is Non-Volatile type of memory i.e it does not lose its content when the power supply to it is switched off. A motherboard normally contains one or more of these ROM chips. The memory capacity of a ROM varies from one type of system to another.64 KiloByte (KB) was normally sufficient for a XT system, whereas as AT system requires 256KB of ROM. BIOS What is BIOS' BIOS is an abbreviation if Basic Input Output System. It is one of the most important program stored in the ROM. BIOS program lets your application program and the hardware such as floppy disk, hard disk, video adapter etc. communicate with each other. It is pronounced “bye-os”. The BIOS also contains a program called Power-On-Self-Test or POST. This post program checks the motherboard and other devices connected to the computer during the system power-on time. IBM made the original BIOS for their copyright product, but many compatible BIOS program BIOS program are available from Award, Phoenix, American Megatrends Inc. (AMI) etc. various manufacturers. CMOS(Complementary Metal Oxide Semiconductor) Memory In old IBM XT or compatible system, BIOS, with the help of jumpers, detected what all components are connected to the computer system. IBM AT and higher systems do not contain these jumper switches and instead use a CMOS memory to store the system configuration, date, and time etc. information. Chapter -1 23 Name : Motherboard This CMOS memory receives power from a battery accompanying it, this battery helps it retains the information stored in it even when the system is switched off. When an AT or higher system is switched on, BIOS matches the information stored inside the CMOS with the components connected to the system and if it finds some mismatch or error, the BIOS displays some error message, explaining the problem. Cache Memory: A small amount (normally less than 1MB) of high-speed memory residing on or close to the CPU. Cache memory supplies the processor with the most frequently requested data and instructions. Level 1 cache (primary cache) is the cache closest to the processor. Level 2 cache (secondary cache) is the cache second closest to the processor and is usually on the motherboard. Support Chips/Chipsets Apart from the processor chip and the memory, Motherboard also contains many controller chips and other devices which everything together. A typical system required interrupt controller, DMS controller, Timer chip, Clock chip, Bus controller chip, I/O peripheral interface chip etc, to make the computer work as a complete unit. The IBM PC, XT, AT, Pentium etc. use standard Inter chips intended for any computer built around an Intel CPU. Modern developments in electronics have made it possible to produce VERY LARGE SCALE INTEGRATED CIRCUITS(VLSIC), and now just two or three of these VLSIC chips can do the work which were previously performed by dozens of different chips. These set of VLSIC chips are called ‘CHIPSETS’. A typical chipset contains in one or two VLSIC chips all the support logic required by the processor to function as a complete system. Many of these chipset maker include serial and parallel ports, floppy and hard disk controllers, USB support, LAN and audio support, and display adapter on the chipset itself. Large-scale integration along with high –capacity memory chips has let to even fewer components on a PC’s motherboard. Motherboard Configuration A typical motherboard has several options and proper configuration is required to select the required hardware setup. Most of the PC and XT class motherboards are set/configured using jumpers or switches on the motherboard. In the AT and later machines, the configuration options are stored in CMOS RAM and are set using the SETUP utility in the BIOS ROM. The motherboard configuration should always be perfect, as an incorrectly setup motherboard can cause the system to malfunction or even crash. Summary 1. Motherboard is the main circuit of PC. 2. It holds important components like CPU, Memory, SMPS etc. 3. Integrated motherboards have features such as graphics, LAN, audio, etc integrated onto the motherboard and aim at providing solutions for the cost-conscious users. 4. Form factors of motherboard are Baby-AT, ATX, NLX, LPX. 5. To identify motherboard model, see the white sticker on the side of the last ISA slot or the prints on the board itself. Short questions :- 1. What is a motherboard' 2. Name the components of a motherboard' 3. What is Cache Memory' 4. What is an integrated motherboard' 5. How can I identify the model and manufacturer name for my motherboard' Essay Type questions: - 1. Explain briefly about the Motherboard Form Factors' 2. Briefly explain the components of Motherboard'