using binary coding information remember bit = 0 or 1, binary digit byte = the number of bits used...
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Using BinaryCoding Information
Remember Bit = 0 or 1, Binary Digit Byte = the number of bits used to represent letters,
numbers and special characters such as $ # , / &. Word = number of bytes a computer can process at
one time by the CPU.
So,
Bits form Bytes and Bytes form Words.
Copyright © 2008 by Helene G. Kershner
Using BinaryCoding Information
Two common formats for coding letters, numbers and special characters are:
EBCDIC -- Extended Binary Coded Decimal Interchange Code
8 bit code Originally used in IBM mainframes
ASCII -- American Standard Code for Information Interchange 7 bit code Originally used on non-IBM systems
Copyright © 2008 by Helene G. Kershner
Using BinaryCoding Information
Coding in EBCDIC and ASCII: Letters
Place holder
NumbersPlace holder
Copyright © 2008 by Helene G. Kershner
Using BinaryCoding Information
Codes are organized so that mathematics makes sense They are ordered so that each subsequent number is larger than
the one before.
7 > 5
In ASCII 011 0111 > 011 0101 In EBCDIC 1111 0111 > 1111 0110
Copyright © 2008 by Helene G. Kershner
Using BinaryCoding Information
Codes are designed so that the ordering of English letters makes sense.
A B C D E F … U V W X Y Z Over time we consider this ordering to be fixed The implication is that we can compare letters and that certain
letters appear before others in the alphabet. For Example: A < F and X > F ASCII and EBCDIC code letters so that this concept remains
valid.
Copyright © 2008 by Helene G. Kershner
Using BinaryCoding Information
Codes are designed so that the ordering of English letters makes sense.
A < F
In ASCII 100 0001 < 100 0110
In EBCDIC 1100 0001 < 1100 0110
X > F
In ASCII 101 1000 > 100 0110
In EBCDIC 1110 0111 > 1100 0110
Copyright © 2008 by Helene G. Kershner
Using BinaryCoding Information
Codes are designed so that the ordering of English letters makes sense. At the time of its creation, it was argued that ASCII was a more rational
coding scheme based on the way it codes letters.
Both ASCII and EBCDIC are limiting Both can code all of English and most Romance languages. As computer use has expanded both became incomplete ASCII is still the foundation for text based email on most computers
UNICODE Designed to provide a single coding system for every character in every
natural language
Copyright © 2008 by Helene G. Kershner
Using BinaryCoding Information
Error Checking Transmission errors are a fact of computer life Think of the game of Telephone Power interruptions happen Life happens GIGO
What can be done to reduce or repair errors in transmitted characters?
Copyright © 2008 by Helene G. Kershner
Using BinaryCoding Information
Parity – In common English, Parity means two things are equal
How could this be applied to error checking?
With computers it applies to the special bit added to a
byte so assist computer systems in reducing errors.
Copyright © 2008 by Helene G. Kershner
Using BinaryCoding Information
Odd Parity Look at byte, attach either a 0 or a 1 to force the byte to be odd Examine the byte coded to mean Z
In ASCII 101 1010Count the number of 1s, there are 4, 4 is even, the parity bit
is set to one (1) to make the string of bits odd.
The byte is coded 1 101 1010
In EBCDIC 1110 1001
Count the number of 1s, there are 5, 5 is odd, the parity bit is set to zero (0) to keep the string of bits odd
The byte is coded 1110 1001 0
Copyright © 2008 by Helene G. Kershner