Computer Data Formats

Computer Data Formats:

            For programming the microprocessor understanding of different data formats. This is necessary because in different data formats the same number is represented differently. Following are some of the common data formats used for programming the microprocessor.

 

1)      ASCII data formats

ASCII stands for American standard code for information interchange. It is used to represent alphanumeric characters in the memory of computer system. The standard ASCII code is a 7 bit code with the 8^th bit is used as sign bit or parity bit. (If the ASCII data is used with printer the MSB bit is 0 for alphanumeric printing &1 for graphics printing. In many computer systems extended ASCII characters set is used by placing logic 1 at MSB position. This character set also contain some control characters such as clear screen, backspace; line feed etc.)

2)      Binary coded Decimal (BCD):-

This is another commonly used data formats in computer systems. The range of BCD numbers is from 0 to 9. The BCD data can be represented using either packed or unpacked format. In packed BCD format, 2digits are stored per byte. In unpacked BCD format 1 digit is stored per byte. Table below shows some example & BCD data.

Decimal	Packed BCD	Unpacked BCD
12	0001 0010	0000 0001 0000 0010
623	0000 0110 0001 0011	0000 0000 0000 0010 0000 0011

3)Byte Sized Data (BSD):-

In this data formats one digit is stored per byte. Byte sized data is stored either as signed or unsigned form. The difference between these two formats is that for signed integers the range is -128 to +128 & for unsigned integers it is from +128 to 0. For MSB position the range of signed integers is from 0 to 127. In this format negative integers are represented using 2’s compliment form. Figure below shows representation of byte sized data.

128                 64                       32                 16                   8                4                  2                  1                  ____________________________________________________________________

Unsigned Byte

 

 

-128                 64              32                 16                 8               4                 2                1                    _______________________________________________________________________

Signed Byte

4)Word Sized Data:-

In this data format a word (16 bits) is formed using 2 bytes of data. An important characteristic of this format is that, when a word is stored in computers memory LSB byte is stored in lower memory. Location & MSB byte is stored in higher memory location.

 

For example word size data 1234H is stored in computer memory as follows

 

 

 

The word sized data can also be signed or unsigned.

5) Real Numbers:-

Real number is also as floating point number. This type of number contains two parts called as fraction (mantissa) & exponent (significant). In this format 4 byte real number is called single precision & 8086 byte number is called as double precision. Figure below shows representation of real numbers.