Java Reference
In-Depth Information
CPU
Memory
Storage
Devices
Bus
Input
Devices
Output
Devices
Communication
Devices
F
IGURE
1.1
A computer consists of a CPU, memory, storage devices, input devices, output
devices, and communication devices.
power travel along the bus from one part of the computer to another. In personal computers,
the bus is built into the computer's
motherboard,
which is a circuit case that connects all of
the parts of a computer together, as shown in Figure 1.2.
motherboard
1.2.1 Central Processing Unit
The
central processing unit (CPU)
is the computer's brain. It retrieves instructions from
memory and executes them. The CPU usually has two components: a
control unit
and an
arithmetic/logic unit.
The control unit controls and coordinates the actions of the other com-
ponents. The arithmetic/logic unit performs numeric operations (addition, subtraction, multi-
plication, division) and logical operations (comparisons).
Today's CPUs are built on small silicon semiconductor chips that contain millions of tiny
electric switches, called
transistors,
for processing information.
Every computer has an internal clock, which emits electronic pulses at a constant rate.
These pulses are used to control and synchronize the pace of operations. A higher clock
speed
enables more instructions to be executed in a given period of time. The unit of measurement of
clock speed is the
hertz
(
Hz
), with 1 hertz equaling 1 pulse per second. In the 1990s computers
measured clocked speed in
megahertz
(
MHz
), but CPU speed has been improving continuously,
CPU
speed
hertz
megahertz
