Motherboards & CPUs

Form Factor

Motherboards are classified in several ways, one of which is the 'form factor' a standard laid down as to the size of the board, the type of connectors fitted and where the holes are to secure it to the case. (blah, blah, blah)

Before starting to assemble, or upgrade a PC you must be sure that what you intend to purchase will both fit into and work with your existing hardware. For example the latest DDR memory, while superficially looking like a normal DIMM will not fit into a DIMM socket.

Not all processors will work with any MOBO. A processor built by AMD, or Cyrix, will probably not function if fitted into a MOBO designed for an Intel processor. Indeed with a number if different sockets available to seat the CPU, it may not even fit onto the MOBO.

Fig 1 A PII socket and CPU

Fig 2 A socket 370 for PII, PIII

Fig 3 A PIV socket and heatsink/cooling fan housing

In practice this means either doing some research prior to purchasing the components, or buying what is referred to in the trade as a `Bundle', a matching MOBO and CPU. This is often sold at less than the cost of the two sperate items.

You would be well advised to check on the memory type the MOBO supports, as Memory modules are changing all the time.

The case is probably the most compatible of all the components you are likely to buy.

The other peripherals such as video, sound, modems, storage devices (FDD, HDD, CDROM) and such will, in all but extreme cases work with the PC you are constructing.

Fig 8 A removable backpanel and the ports on a MOBO

Motherboard

Fig 10 A Pentium 4 Motherboard

Fig 11 A Pentium II Motherboard

1 Power supply connectors
2 On board EIDE and floppy disk controller sockets
3 AGP (Accelerated Graphics Protocol) Video socket
4 PCI sockets
5 ISA sockets
6 CMOS clearing jumper
7 Battery
8 Printer and COM ports
9 USB sockets
10 Keyboard and PS2 mouse sockets
11 CPU socket (empty)
12 CPU fan power connector
13 DIMM (Dual In-line Memory Module) sockets

Other MOBO's

In most cases you will only come across MOBO's designed for `Workstation' use, having room for a single processor, however this is not the only type of board available.

A Server, based on a good specification MOBO and Processor will be capable of handling the needs of most small organisations, say 10 - 15 workstations. However as the number of workstations increases true Servers come into their own.

Any reasonable server board will have at least the ability to add a second processor and will invariably have a SCSI interface built onto the MOBO

Fig 12 A dual processor MOBO

Older MOBO's

The design of MOBO's changes so rapidly that the term `older' could be used on a board that is perhaps two, or three years old, however in your dealings with the PC it is as well to be aware of what might be termed `Retro' equipment, so we will look at what you may come across.

Fig 13 a Pentium I Motherboard

Earlier MOBO's such as the one shown above had sockets for both the earlier and now redundant SIMMs and DIMMS

Fig 14 A DIMM (top) and a SIMM

The Processor (CPU)

The current top of the range CPU is the Pentium PIV. `Pentium' is a brand name of Intel, but Intel are not the only processor manufacturers. Other companies such as AMD and Cyrix also produce chips and it could be argued that it's this rivalry that drives them to produce new, faster CPUs every couple of years.

Processors are rated by clock speed, with 2Gigahertz CPU's just around the corner. The clock speed could be likened to a heartbeat, the faster the heartbeat the faster the CPUs ability to perform the calculations needed to provide the, usually visual information we see.

Selecting an appropriate Processor for your MOBO can seem a little daunting, with Most MOBO manufacturers producing a board to suit a particular CPU makers Chip, although it will allow for that chip to be of a number of clock speeds and will almost certainly allow for faster chips than are currently available.

Large numbers of component suppliers will sell you a `Bundle', a MOBO and CPU which will work together. This is often your best bet, as it may be cheaper than buying the two parts seperately.

Modern BIOSs will `autodetect' the CPU and configure themselves, however some require that jumpers, or DIP switches be set to adjust the MOBOs clock speed to suit the CPU

A Processor

Jumpers and DIP switches

Most motherboards require little, if any configuration to work, however some need to have either jumpers, or DIP switches set to configure details such as bus clock speeds

Fig 16 A jumper and a DIP switch

The BIOS

BIOS stands for Basic Input Output System. It is the first item of software run Your computers hardware must interface with software and the BIOS allows it to do this. It could best be described as a small program on a chip which allows you to run software from floppy disk drives (FDD), hard disk drives (HDD), or if installing software the CDROM.

Modern BIOS's are top configuring, needing only the current Time and Date to be input by the user.

They will automatically detect the type of Processor installed and its operating voltages, the type and size of any hard disks, CDROMS, zip drives, etc.

Fig 17 the BIOS screen

The BIOS is enables the PC to boot and provides a basic set of instructions, performing the tasks that need to be done at start-up such as the POST (Power-On top Test, booting an operating system from FDD, HDD or CDROM). It also provides, for the operating system, an interface to the underlying hardware in the form of a library of interrupt handlers. For instance, each time a key is pressed, the CPU performs an interrupt to read that key. This is echoed by the other input/output devices such as Serial and parallel ports, video cards, sound cards, hard disk controllers.

You should be aware that some older PC's cannot interface with some modern hardware because their BIOS does not support that hardware.

The hardware configuration is stored in the CMOS, or Complementary Metal Oxide Semiconductor. To work properly the BIOS needs to know the hardware configuration parameters. These are permanently saved in the CMOS RAM. The CMOS power is supplied by a battery, so the data is not lost when the PC is turned off. As with all batteries it will eventually fail, at between 3 - 5 years and need to be replaced. Its replacement is covered later in this course.

Your PC's performance is greatly affected by the CMOS settings. This is because the CMOS setup permits you to specify how fast your computer reads from memory, whether or not your cache is enabled or disabled, whether or not your CPU's cache is enabled or disabled, how fast your PCI bus communicates with its adaptor cards and a lot more. For more information on optimizing these performance settings, refer to the MOBO manual.

Plug-and-Play (PnP)

This refers to the ability of the computer system to automatically configure expansion boards such as sound cards , video cards, modems and other devices. PnP does away with the need to set DIP switches, jumpers, or other configuration elements.

After installing the component and restarting the PC, the OS recognises that the new hardware is present. If the drivers for the device are in the OS's drivers library it will automatically load them, if not it will ask you to insert the driver disk, or CDROM supplied with the hardware, and load from there.

Most modern PCs have a flash BIOS, This means that the BIOS has been recorded on a flash memory chip, which can be updated if necessary. The updates are available from the MOBO manufacturers web site and the board is supplied with the instructions to carry out that update.

The BIOS is fairly standardized, so all PCs are similar at this level (although there are different BIOS versions). Additional DOS functions are usually added through software modules. This means you can upgrade to a newer version of DOS without changing the BIOS.

All current PC BIOS's can handle Plug-and-Play (PnP) devices, and are known as PnP BIOS's, or PnP-aware BIOS's. These BIOS's are always implemented with flash memory rather than ROM.

Changing the BIOS Settings

Under normal circumstances you will have no reason to alter the BIOS settings as they are automatically optimised when the PC is first turned on, however there may be circumstances where you will need to manually set a parameter.

The BIOS setup is usually accessed by pressing the <DEL> key on start-up. A careful watch of the start-up screen will indicate which key to press.

Setup is the set of procedures enabling the configure a computer according to its hardware characteristics. It allows you to change the parameters with which the BIOS automatically configures your chipset. The original IBM PC was configured by means of DIP switches buried on the Motherboard. Setting PC and XT DIP switches properly was something of an arcane art. DIP switches/jumpers are still used for memory configuration and clock speed selection. When the PC-AT was introduced, it included a battery powered CMOS memory which contained configuration information. CMOS was originally set by a program on the Diagnostic Disk, however later clones incorporated routines in the BIOS which allowed the CMOS to be (re)configured if certain magic keystrokes were used.

As the chipsets controlling modern CPUs have become more complex, the number of parameters you can specify in setup has grown. Unfortunately, there has been little standardization of terminology between the half dozen BIOS vendors, three dozen chipset makers and large number of Motherboard vendors. Complaints about poor Motherboard documentation of SETUP parameters are very common.

To exacerbate matters, some parameters are defined by BIOS vendors, others by chipset designers, others by Motherboard designers, and others by various combinations of the above. Parameters intended for use in Design and Development, are intermixed with parameters intended to be adjusted by technicians, who are frequently just as baffled by this stuff as everyone else is. No one person or organization seems to understand all the parameters available for any given SETUP.

You should bear in mind that if you have configured a parameter and caused an error, you have the option in the BIOS setup to return the configuration to the factory settings and start again.

POST (Power-On top Test)

This test is performed whenever the PC is turned on. It counts and checks the memory, identifies the drives attached and will allow access to the BIOS setup.

Fig 18 The POST screen

The Battery

The CMOS and the information kept in it, such as the Time, Date, Types of hard drives, is kept powered by a battery mounted on the MOBO. The battery is kept charged by the MOBO, but after a few years (3-5) will fail. This may show ittop in a number of ways, such as losing the Date/Time, or a "CMOS Checksum error" warning when the PC is turned on.

Fig 19 The battery

This battery Is usually of the type `CR2032', costs about £2.00 and takes about 2 minutes to change. The procedure is as follows:

Fig 20 Releasing the battery clip

(1) Open the PC case and locate the battery.

(2) Using a ball point pen, or small screwdriver, push the clip away from the battery in the direction shown. The battery will rise out of the holder.

(3) Insert the new battery, firstly by hooking it under the lip at the front of the battery holder and pressing it down onto the clip. The clip will move out of the way and click back when the battery is seated properly.

Memory Installation

Is covered in the section on memory

© Allen. C. Roffey primerpc.com 15:19 07/06/2005