a. General. Unfortunately the decimal system does not lend itself to convenient implementation in

digital systems. It is very difficult to design equipment so it works with ten different voltage levels, each

one representing one of the decimal characters 0 through 9. On the other hand, it is very easy to design

electronic circuits that operate with only two different voltage levels. For this reason the binary (base 2)

although other systems are often used in conjunction with it.

b. Characteristics. The binary number system has two binary digits called bits which are assigned

the symbols 0 and 1. The binary system is also a positional value system. Each binary digit has its own

value or weight expressed as a power of two. An example of a binary number is 1011 which is read as

ONE-ZERO-ONE-ONE. The number 1301 is not a binary number, since 3 is not a binary digit. The

right-most digit is the least significant digit (LSD) and carries the least weight while the left-most digit is

the most significant digit (MSD) and carries the most weight.

c. Conversion of Binary.

(1) General. In computer work, it frequently happens that a value stated in one number system

has to be converted to that same value in another number system. Unless conversions are made

accurately, computer operations and output become meaningless.

(2) Positional Notation. By conversion agreement, a radix point is not written except when

necessary to separate the integral and fractional parts of an expression. In writing 100.00, only 100 is

written. The .00 portion is ordinarily discarded because it is meaningless and unnecessarily uses up

computer capacity. On the other hand, the radix point is needed in writing numbers such 11.1 because the

number contains both integral and fractional parts. If the radix point were omitted, the expression would

be understood as 111, which is entirely different from the original number. In fact it equals 11.1

multiplied by the radix. Further, moving the radix point one position to the left in 11.1 yields 1.11 and

this quantity is equal to 11.1 divided by the radix. This property of the radix point position is the basis of

the powers-of-ten method of simplifying the multiplication and division of decimal numbers. This

concept will be put to use later in this text to aid in converting from decimal to binary and decimal to

octal. Most digital computers are built to handle their internal operations in the binary system, while

reading in and out in the decimal system. This requires the computer to convert, with correct positional

notation, all of its inputs and output.

(a) The table in Figure 1-3 covers conversion of binary numbers to decimal numbers and

conversion of decimal numbers to binary numbers.