Personal Computer - Character Codes.
Over the years, a number of codes were developed to represent sets of characters. These characters/symbols may be just alpha characters, numbers, and special characters. The number of bits used in a code, determines the number of symbols that can be represented by the code.
For instance, since the codes are going to be in binary, the values of each bit can only be 1 or 0, a two value. So, the power of 2 used determines how many symbols it represents:
5 bits = 32 - BAUDOT Code
7 bits = 128 - ASCII Code
8 bits = 256 - Extended ASCII and EBCDIC
First, in today's world the codes used are usually Extended ASCII and EBCDIC. Both are 8 bit codes, and can represent a maximum of 256 characters.
ASCII = American Standard Code for Information Interchange. EBCDIC = Extended Binary Coded Decimal Interchange Code. EBCDIC code is used in many IBM computers and in frames being transmitted on LANs. Extended ASCII is the first code that allowed us to represent enough characters to include graphic characters in the code. Extended ASCII code was the break needed to actually represent things such as the boxes and colors that you see at this time!
OK - each character or symbol you see is made up of 8 binary bits. The combinations of bits represent different characters/symbols to the computer. The EBCDIC and ASCII codes do not have the same bit configuration to represent the same character.
Here is the EBCDIC Code Chart:
On the left side of this chart you see the bit positions from 8 to 5 and above and to the right you see the 4 to 0 bits. If you see a string of bits like this "11000101", the first or left hand bit is the 8 bit, and the rightmost is the "0" bit. They go left to right from the most significant to the least most significant digit or bit. To convert this pattern or set of bits to an actual character, or symbol we would search the left side until we found the "1100" in bits 8 thru 5. That is the row with the capital letters of the alphabet. Then, we look across the top to find the pattern "0101". The we go to the cell on the chart where the row and the column intersect. In this case, it at intersects at the "E" space, so in EBCDIC, "11000101" is an alphabetic "E".
Every character defined can be interpreted in this manner. Normally, you will have no need to convert such characters, but occasionally, if you have to interpret a "frame" from a network, you use EBCDIC conversion.
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