270 DIGITAL BUILDING BLOCKS AND COMPUTER SYSTEMS
f(t)tvtt 0 t 1f 1 = 1f 0 = 0
t 2 t 3 t 4 t 5 t 6
(a)(b) (c) (d)vtvt0
00 − 5− 5+ 5
+ 5Figure 6.0.3Typical binary signals.transistors and diodes, as well as resistors and capacitors, on a very small chip (no larger than a
pencil eraser). The variety of ICs available to process digital signals can contain a few to several
thousand components on a single chip. A convenient method of digital IC classification, based
on the number of components per chip, is as follows:- Small-scale integration (SSI), containing fewer than 100 components
- Medium-scale integration (MSI), containing 100 to 1000 components
- Large-scale integration (LSI), containing 1000 to 10,000 components
- Very large-scale integration (VLSI), containing more than 10,000 components
Digital computers and other large digital systems use mostly LSI and MSI chips. The number
of components per chip has increased from about 100 in the 1960s to 10^8 in the 1990s. Speed,
power consumption, and the number of gates (switches) on the chip are three of the more important
characteristics by which digital ICs are compared.
The general-purpose digital computer is the best known example of a digital system. Other
examples include teletypewriters, word processors, dial-telephone switching exchanges, fre-
quency counters, remote controls, and other peripheral equipment. Manipulation of finite, discrete
elements of information is a characteristic of a digital system. Information in digital systems is
represented by signals (currents or voltages) that take on a limited number of discrete values and
are processed by devices that normally function only in a limited number of discrete states. A
great majority of present digital devices arebinary(i.e., have signals and states limited to two
values) because of the lack of practical devices capable of performing reliably in more than two
discrete states. Transistor circuitry, which can be constructed with extreme reliability, has two
possible signal values, either on state or off state. With the advent of transistors, the computer
industry flourished.
To start with, this chapter presents basic digital building blocks, which are usually designed to
process binary signals. Then the digital system components are discussed. Later on an introduction
to computer systems and networks is included. Thus, a basic foundation of digital systems is laid
out for the reader.