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There are many codes in computer system which may remain unnoticed by many computer geeks and nerds.  I also first didn’t see it but I am going to share it because these are important codes and used by many computer hardware developers, vendors and computer software developers.   They are mostly understood by ELECTRONICS AND ELECTRICAL ENGINEERING geeks or nerds.  They are as under :




First we will discuss something about ERROR DETECTION CODES.                                                                                                          




Binary information , be it pulse modulated signals or digital computer input or output, may be transmitted though some form of communication medium or electrical wires or radio waves.  Any external noise introduced into physical communication medium or electric wires changes bit values from 0 to 1 or vice versa.  An error detection code can be used to detect errors during transmission.  The detected error cannot be corrected but its presence is indicated.  The usual procedure is to observe the frequency of errors.  If errors occur only once a while, at random and without a pronounced effect on the overall information transmitted then either nothing is done or particular erroneous message is transmitted again.  If errors occur so often to distort the meaning of the received information, the system is checked for malfunction.  A parity bit is added at the end of the message to make the message to become odd if it is even or make it even if it is odd.  I am talking about the binary numbers generated by the software from the message that is passed ,  during transfer of information from one location to another, the parity bit is handled as follows.  In the sending end, the message (in this case the first four bits) is applied in “parity generation” where the parity bit is generated.  The message as well as the parity bit is transferred to its destination.  In the receiving end the message which is converted to binary numbers are taken with along with the parity bit into the parity bit network to check the parity bit.  An error is generated if the parity bit is not the same as generated or let’s says an error is detected if the checked parity does not correspond to the adopted one.  The parity method detect the presence of one, three, or any old combination of errors.   An even combination of errors is undetectable. 




Many applications of digital computers required the handling of data that consist not only of numbers, but also of letters.  For instance, an insurance company with millions of policy holders may use a digital computer to process its files.  To represent any policy holders may use a digital computer to process its files.  To represent the policy holders name in binary form, it is necessary to have  binary code for that alphabet.  In addition, the same binary code must represent decimal numbers and some other special characters.  An alphanumeric (sometimes abbreviated alphanumeric) code is a binary code of a group of elements consisting of ten decimal digits, the 26 letters of the alphabet and a certain number of special symbols such as $.  The total number of elements in an alphanumeric group is greater than 36.  Therefore, it must be coded with a minimum of six bits (26 = 64, but 25 = 32 is insufficient).  One possible arrangement of a six bit alphanumeric code is also called internal code.  The need to represent more than 64 characters (the lowercase letters and special control characters for the transmission of digital information) gave rise to seven- and eight-bit alphanumeric codes.  One such code is known as ASCII( American Standard Code For Information Interchange);  another is known as EBCDIC(Extended Binary Code Decimal Interchange Code).  Let us discuss something about ASCII codes : In ASCII code listed in various books  consists of seven bits,  but is for all practical purposes an eight bit code , because an eight bit is used as parity.  When discrete information is transferred through a punch card, the alphanumeric characters is used 12bit binary code.  A punch card contains 80 columns and 12 rows.  The 12 rows are marked starting from the 12 the row and preceding backwards such as 12, 11, 10, 9, 8 and so on punches.  The first three are called zone punch and last nine are called numeric punch.  The 12 bit card code can be seen through internet searches.





Digital systems can be designed to process data in discrete form only.  Many physical systems supply continuous output data.  These data must be converted into digital or discrete form they are applied to a digital system.  Continuous or analog information is converted into digital form by means of analog to digital converter.  It is sometimes convenient to use the reflected code to represent  digital data converted from analog data.  The advantage of the reflected code over pure binary numbers is that a number in the reflected code changes by only one bit as it proceeds from one number to the next.  A typical application of the reflected code occurs when the reflected code occurs  when the analog data are represented by a continuous change of a shaft position.  The shaft is partitioned into a segments, and each segment is assigned a number.  If theadjacent segments are made to correspond to adjacent reflected code numbers, ambiguity is reduced when detection is sensed in the line that separates any two segments.   



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