Hardware Reference
In-Depth Information
The basic system board incorporates a CPU, provides a connector for the
addition of a maths coprocessor, incorporates bus and DMA control, and pro-
vides the system clock and timing signals. The system board also houses the
BIOS ROM, main system RAM, and offers some limited parallel I/O. It does
not, however, provide a number of other essential facilities including a video
interface, disk, and serial I/O. These important functions must normally be
provided by means of adapter cards (note that some systems which offer only
limited expansion may have some or all of these facilities integrated into the
system board).
Adapter cards are connected to the expansion bus by means of a number of
expansion slots (see Chapter 2). The expansion cards are physically placed so
that any external connections required are available at the rear (or side) of the
unit. Connections to internal subsystems (such as hard and floppy disk drives)
are usually made using lengths of ribbon cables and PCB connectors (see later).
A typical Pentium system motherboard layout is shown in Figure 1.11. This
system board provides five and a single AGP card slot. Two three-terminal inte-
grated circuit voltage regulators provide the low-voltage 3.3 V supply required
by the faster Pentium processors. The 296-pin ZIF socket ('Socket 7') is suitable
for a wide variety of devices, including all 6x86 and Pentium chips (including
MMX) as well as the AMD K5 and K6. 512 KB of surface mounted cache
memory is fitted. Two 168-pin sockets accept up to two dual-inline memory
modules (DIMM) carrying fast (6-7 ns) synchronous DRAM or EDO DIMMs.
Once again, standard 'primary' and 'secondary' IDE hard disk drive and/or
CD-ROM ports are provided by means of two 40-way connectors.
Various combinations of DRAM can be fitted, with 128, 256 and 512 MB
being the most popular. Standard IDE hard disk drive and/or CD-ROM ports
are provided by means of two 40-way connectors (these are the 'primary' and
'secondary' IDE ports). Note that the floppy disk interface is provided as part
Photo 1.8
AMD Athlon processor fitted with a CPU fan
