The Motherboard: Heart of the PC.

We spoke of the CPU (Central Processing Unit) as the brain of the PC; the motherboard can be likened to the heart of the system. The beat of the RTC (Real Time Clock) and the flow of instructions and data through the various buses can be thought of as a combination of the circulatory and nervous systems. In appearance, the motherboard is a large printed circuit at the bottom of a desktop case or along the side of a tower case. Components on the motherboard are either plugged into sockets or hard-wired (soldered to the board). The “power” of a motherboard is a function of the combination of CPU and the system chipset. The pairing of the two is very specific and has limited choices. The choice of the CPU will also define the type of motherboard.

Everything connects to the motherboard: the CPU, RAM, the kick-start BIOS, cards for video, sound and all sorts of peripherals. Some motherboards contain integrated systems for sound, video, and/or communication. This is primarily a cost-saving or form factor decision for the manufacturer. Some of these systems allow the disabling of the integrated applications and their replacement with plug-in cards. However, this requires a case designed to accept the cards – thus compromising the goals of lower cost and space.

We have mentioned a few of the components on the motherboard. The list also includes a number of memory circuits. The most talked about memory component is RAM (Random Access Memory). The hub of activity, it is where programs and files loaded on the hard drive go to work. A speedy companion to RAM is the L2 cache memory. It is composed of faster logic elements (transistors) to form SRAM (Static RAM) memory. The popular RAM actually refers to a family of DRAM (Dynamic RAM) which must be constantly refreshed (rewritten). The L2 cache serves as a repository of recently accessed operation instructions and data on the idea that they will soon be called upon again. For a cycle of processing, the contents can get to the CPU much faster than from the larger RAM. For recent high-end units, the L2 cache has multiplied in capacity and is now on the real estate of the CPU.

The system chipset is a distinguishing feature of the motherboard. Different chipsets, paired with identical CPU's, vary in performance. Their role is to communicate with the other motherboard circuits, adapter card connectors, and disk drives. They assure compatibility between ISA (the older Industry Standard Architecture) and PCI (Peripheral Component Interconnect) buses, along with communication with the EIDE (Enhanced Integrated Drive Electronics) disk storage interface. The chipset is also where the aforementioned integrated circuits, such as the graphic drivers, are stored. When people refer to the motherboard chipset, they most often mean just the northbridge and the Southbridge chips, also known as the front-side bus. The Northbridge is the single chip in a core-logic chipset that connects the CPU to the system memory and the AGP and PCI buses. The Southbridge controls the IDE bus, USB, plug-n-play support, the PCI-ISA Bridge , keyboard/mouse controller, power management features, and other peripherals.

PCI slots accept a host of adapter cards: sound, network, SCSI (Small Computer System Interface) and many more. PCI slots have supplanted the ISA slots. Today, ISA is typically used for legacy hardware and has a speed of about 16MBps, compared to the PCI of 127MBps.

A fairly recent addition to the motherboard is the AGP ( Accelerated Graphics Port ) slot for video cards. The bus communicates directly with the main RAM memory, reducing the load on the PCI bus and the CPU. In 1999, the AGP4X (four times) was introduced, enabling transmissions at 1024MBps. This high speed port allows for easy (though not inexpensive) upgrades of the video graphics system. The latest video cards have on-board memory to further reduce the load on the CPU and system bus.

The connectors for floppy drives, hard drives, CD-ROMs, CD-R/RW, and DVD variants tie these devices to the motherboard via ribbon cables – multiconductor flat wire assemblies. The floppy drive has a connector all to itself. The Primary and Secondary EIDE connectors allow for four devices, two per connector. The ribbon cables have a third connector near the center. Each EIDE channel must be set in a Master or Slave configuration and traffic is controlled by IRQ (Interrupt Request) and separate I/O (Input/Output) addresses. Care should be taken as to how you connect devices to the EIDE bus. If you connect a slower device, such as a CD-ROM, on the same bus as a fast hard drive – it will drag the bus speed down to the slower device speed.

Other I/O ports connect the mouse and keyboard through PS/2 (round 6-pin DIN [Deutsche Industrinorm]) connectors on the back of the case. The parallel port, also denoted by the archaic LPT (Line Printer Terminal), is typically used for the printer. The serial port(s), also known as the COM (for Communications) ports, is used for the modem (modulator/demodulator), your access to the Internet, as well as other peripherals such as game joy sticks.

A late addition to the family of ports is a good reason to upgrade an older PC – the USB (Universal Serial Bus). Presently in two flavors USB 1.1 and USB 2.0, with respective transmission speeds of 12MBps and 480MBps. Of course, in the real world, you will seldom (if ever) see these numbers. To use USB 2, devices must be made with that technology. However, older USB 1.1 devices will work with USB 2, since it is backward compatible. A great feature of USB technology is that it is hot-swappable – there is no need to power off the PC when attaching and removing devices. A cautionary note here – you may have to click on a piece of software prior to removing a device. With Windows' Plug and Play, devices are immediately recognized when attached to a PC. The list of USB enabled devices is extensive; from printers, scanners, digital cameras, removable memory units, and more.

With the drive by OEMs (Original Equipment Manufacturers) to reduce costs we may soon see the end of floppy drives being included in PCs. CD-R/RW drives now populate even the lowest tier of inexpensive computers. The CD's capacity of 700MB, its ruggedness, its compact form factor, and declining cost make it an admirable heir to a floppy with its miniscule storage, susceptibility to EMF (Electro-Magnetic Fields) and refrigerator magnets. The new USB and Firewire (IEEE 1394) ports could very well herald the end of the parallel and serial ports.