Hardware Reference
In-Depth Information
Figure 1.8
Development of the 'x86 Intel processor family
Figure 1.8 shows the development of x86 processor technology into the
modern Pentium family of processors whilst Figure 1.9 shows how the relative
power of PC processors has increased over the last two decades.
PC architecture
The generic PC, whether a 'desktop' or 'tower' system, comprises three units:
system unit, keyboard, and display. The system unit itself comprises three items:
system board, power supply, and floppy/hard disk drives.
The original IBM PC System Board employed approximately 100 IC devices
including an 8088 CPU, an 8259A Interrupt Controller, an optional 8087 Maths
Coprocessor, an 8288 Bus Controller, an 8284A Clock Generator, an 8253
Timer/Counter, an 8237A DMA Controller, and an 8255A Parallel Interface
together with a host of discrete logic (including bus buffers, latches, and
transceivers). Figure 1.10 shows the simplified bus architecture of the system.
Much of this architecture was carried forward to the PC-XT and the PC-
AT. This latter machine employed an 80286 CPU, 80287 Maths Coprocessor,
two 8237A DMA Controllers, 8254-2 Programmable Timer, 8284A Clock
Generator, two 8259A Interrupt Controllers, and a 74LS612N Memory Mapper.
In order to significantly reduce manufacturing costs as well as to save on
space and increase reliability, more recent AT-compatible microcomputers are
based on a significantly smaller number of devices (many of which may be
surface mounted types). This trend has been continued with today's powerful
386- and 486-based systems. However, the functions provided by the highly
