BIOS (Basic Input Output System):
A small code of instructions etched into a ROM chip and put on the motherboard. The BIOS is the most crucial component of a motherboard. It determines and detects what kind of hardware is present on your motherboard. When your system starts, the processor looks for its first instruction in the BIOS. Hardware is identified, and the operating system starts up. Initially, BIOS came in EEPROM (Electrically Erasable Programmable Read Only Memory) chips. The problem with these was that the BIOS code couldn’t be updated. So for example, if a new processor was introduced and your motherboard didn’t support it, you had to buy a new motherboard. Later, a new type of ROM was introduced, called the flash BIOS, which is also popular today. You could update the BIOS code here using a software program. Motherboards that use chipsets like the Intel 810 are likely to have their BIOS embedded within the chipset itself. Flash BIOS offers many advanced features, such as the ability to change the processor clock speed and setting soft power options through the BIOS itself, which once had to be set using jumpers.
Slots and sockets
The processor slot or socket on a motherboard determines which processor your motherboard supports. The following are the most-commonly used sockets on motherboards.
Socket 7: Motherboards with this type of slot can house the Pentium class of processors, including Intel’s Pentium range, AMD K6-2 and 3, Cyrix MII, and IDT Winchip. The processor in this socket is mounted horizontally. Today, these motherboards are identified as Super Socket 7. The difference is that Super Socket 7 motherboards contain an AGP port and USB support.
Socket 370: This socket is similar in appearance to Socket 7, except that it supports only Intel Celeron processors. In this category, 433 MHz Celerons are now commonly available.
Slot 1: Intel first introduced this slot for its PII processors. Later, it also introduced its Celeron processors on it, but moved them to Socket 370 subsequently. Slot 1 now also supports PIII processors. Slot 1 mounts the processor vertically, similar to a normal add-on card. The processor is mounted on a PCB (Printed Circuit Board) that contains the L2 cache.
Slot A: When Intel patented its Slot 1 design, other processor manufacturers had to resort to other slot designs, and that’s how Slot A came into the picture. This slot is designed for AMD’s Athlon processor. The interface is mechanically compatible with Slot 1, but has different electrical connections, so that the Athlon and the PIII can’t be exchanged for each other.
Here, we’ve provided details on the two types of memory slots. For more on memory, read the article “All about RAM”, page 142 in this issue.
SIMM: Short for Single In line Memory Module. SIMM slots were quite common in Socket 7 motherboards, and housed the earlier asynchronous DRAM, such as EDO RAM. However, motherboards today no longer have SIMM slots.
DIMM: Short for Dual In line Memory Module. This RAM slot is found in all new motherboards. It houses Synchronous DRAM, or
A small portion of motherboards is devoted to connectors for external peripherals, such as hard disks and floppy drives. You have different types of connectors, which include:
IDE: Short for Integrated Device Electronics. This interface is used to connect hard drives and other ATAPI (AT Attachment Packet Interface)-compliant devices such as CD-ROM drives, CD-Writers, etc. A motherboard usually has two IDE ports, termed as primary and secondary. You can connect two devices to each IDE port, which are then termed as master and slave devices. You have to change the jumper settings on each device to determine whether it’s master or slave. Usually, the primary master is a hard drive on which the operating system is loaded. The latest motherboards come with support for the new UltraATA/66 specification. This allows hard disks to achieve burst transfer rates of 66 MB/sec. An UltraATA/66 IDE cable is different from the normal one, so ensure that the motherboard you buy has that cable.
FDD connector: This floppy drive port is similar to an IDE connector, except that it has fewer pins. It’s usually placed with the other two IDE ports.
USB (Universal Serial Bus): All motherboards have provision for this port, but some don’t provide the connectors for it. A motherboard usually has two USB ports. USB is an interface that allows a maximum of 127 devices to be daisy chained one after the other. The transfer rates are also pretty high, reaching 12 MB/sec. USB ports are plug-n-play, that is, any device connected to it gets recognized immediately.
Firewire (IEEE-1394): Firewire was developed to meet the demands of today’s audio and video applications. It’s extremely fast, with transfer rates of 400 MB/sec, and even faster speeds are being developed. Firewire supports three different rates–100 MB/sec, 200 MB/sec, and 400 MB/sec. A maximum of 63 devices can be connected by daisy chaining them through two “game boy” type connectors that have six pins each. Firewire technology is expensive, but is applicable in areas where the work involves a lot of digital video.
This is a term meant to identify slots for inserting add-on cards in a motherboard. “Bus” refers to a set of lines that help in transferring data between the CPU and other devices. Here are the various buses found on motherboards:
ISA (Industry Standard Architecture): IBM introduced this 8-bit bus architecture in 1981. It had a theoretical transfer rate of 4 MB/sec. In 1984, with the release of the 286 data processor which used a 16-bit data path, the ISA bus was expanded to 16 bits. The theoretical transfer rate for this was 8 MB/sec. The 16-bit ISA bus is still in use on many motherboards today. A major disadvantage of this bus was that IRQs had to be manually defined through jumpers on cards that mounted on the bus.
MCA (Micro Channel Architecture): The release of the 32-bit 386 resulted in IBM coming out with the MCA bus. IBM wanted to replace the ISA bus with it, but the two were totally incompatible. IBM also insisted that vendors using MCA pay a royalty to them. Due to this, the bus didn’t last too long.
VESA (Video Electronics Standard Association): The VESA bus developed by NEC, also known as the VL (Video Local) bus, came into existence in August 1992. Unlike its predecessors, it ran at the speed of the processor rather than at a speed of 8.33 MHz. It could even access memory at the same speed and gave a theoretical throughput of 128 to 132 MB/sec. It was popular only for two years, as it was compatible only with the 486 processor and FSB speeds of 33 MHz.
PCI (Peripheral Component Interconnect): Another bus specification spearheaded by Intel in 1992, and currently found on all motherboards. The PCI bus required an additional bridge chip to connect to the I/O of the CPU, rather than directly tapping into the processor bus as the VL bus did. This allowed it to use the system bus and take full advantage of the CPU’s data path. PCI runs at 33 MHz and gives a throughput of 132 MB/sec. Another important feature of PCI is that it was the model for the PnP (plug-n-play) specification, which meant that PCI cards could be configured via software, rather than through jumpers as was the case with ISA cards.
AGP (Accelerated Graphics Port): The AGP port is a dedicated graphics port based on PCI. It’s a dedicated point-to-point channel that enables the graphics controller to access main memory, bypassing the bottleneck of the PCI bus. It allows textures to be stored in main memory rather than video memory. The AGP channel is 32 bits wide and runs at 66 MHz, giving a bandwidth of 266 MB/sec. AGP also supports two optional faster modes, giving throughputs of 533 MB/sec and 1.07 GB/sec.