Computers and Programming - Multimedia Introduction to Programming Using Java - page 4

our ability to connect peripherals and the speed and flexibility of the connections
has changed tremendously. For example, just ten years ago it was necessary to
shut down a computer in order to attach most peripheral devices like hard drives
and network connections. Wireless and ethernet were not available to consumers.
Today we use USB (Universal Serial Bus) and firewire (spearheaded by Apple)
to connect most peripherals, and we can just “plug and play”.

The CPU
The central processing unit, or CPU, is perhaps the hardest part of the organ-
ization to understand. Its main purpose is to continually fetch instructions from
memory and execute them. An instruction might be an addition, a subtraction, a
test for one value being less than another, a command to store a value in a par-
ticular part of memory, a command to write a value onto the hard disk, and so on.
CPUs have various registers in which to store temporary values.

fetch next
instruction from
memory

decode
the
instruction

execute
the
instruction

registers
(hold information
temporarily)

the CPU

A CPU is usually on a small chip , a piece of silicon with wiring on it and
with a metal housing and connectors to the outside. The chip in your computer
might contain several million electrical elements, called transistors , all wired
together.
Some computers have two CPUs, which share the load of executing instruc-
tions. Also, most chips these days speed performance by carrying out several
instructions at a time. Almost all computers have a graphics card, which provides
an interface to the monitor and does much of the processing needed to make the
monitor function quickly and smoothly. There is also a cache , where data that is
used frequently is stored so that it does not have to be fetched from memory or
the hard disk every time it is required. Such features complicate the logic of the
CPU tremendously.

Activity
1-1.2

ethernet, wireless connection

scanner keyboard

memory CPU mouse

zip drive

printer

monitor

hard drive

...

Figure 0.1: Simplified view of a computer system