Hardware Reference
In-Depth Information
Figure 1.4
Data conversion: (a) serial-to-parallel and (b) parallel-to-serial
and a computer system enclosure). Serial data transmission over any appre-
ciable distance requires additional line drivers to provide buffering and level
shifting between the serial I/O device and the physical medium. In addition,
line receivers are required to condition and modify the incoming signal to TTL
levels.
The processor
The processor, or
central processing unit
(CPU), is crucial in determining the
performance of a PC and processors (see Table 1.4) have been consistently
upgraded since the first PC arrived on the scene in 1981. Not surprisingly given
the advances in semiconductor technology, the latest processors offer vastly
improved performance when compared with their predecessors. Despite this, it
is important to remember that a core of common features has been retained in
order to preserve compatibility. Hence all current CPU devices are based on a
superset of the basic 8088/8086 registers. For this reason it is worth spending a
little time looking at the development of processor technology over the last two
decades.
The x86 processor family
The original member of the x86 family was Intel's first true 16-bit processor
which had 20 address lines that could directly address up to 1 MB of RAM.
The chip was available in 5, 6, 8, and 10 MHz versions. The 8086 was designed
