When a number, letter of the alphabet or special character is read from an input device into main computer storage or is moved from one location to another, the character is stored using its assigned bit configuration. Once a character or bit configuration has been stored in a location in main computer storage, it will remain in that location until another character is placed in the same location.
This feature of main computer storage has two important consequences. First, once data is placed in a location in storage, it will remain there until changed. This allows the program to reference the data for any processing which might be required while the program is being executed.
Second, since data which is moved to or read into a particular location in storage replaces the data which was stored there, a single set of instructions in a computer program which reference particular locations in main computer storage can be used to process many different records which would each be stored in the same storage locations as they are processed. This ability enables a computer programmer to write one sequence of instructions which can process hundreds or thousands of different records.
Figure 4-10 illustrates the processing that occurs as a series of area codes are entered into computer storage from a computer terminal. The first area code, 212, is entered from the terminal and is stored at storage locations 6000, 6001, and 6002. The field, once in storage, would then be processed as required.
When the second area code, 714, is entered from the terminal, it is also stored in storage locations 6000, 6001, and 6002. It replaces the value 212 which was previously stored in these locations. Area code 714 can then be processed by the same instructions which processed area code 212.
Posts Tagged ‘Letter Of The Alphabet’
Use of main computer storage
Saturday, August 28th, 2010Computer instructions
Wednesday, August 11th, 2010The operations performed by a computer are controlled by a computer program. A computer program consists of instructions to the electronics of the computer system to process data in some manner. Program instructions are stored in main computer storage as machine language instructions which the electronic circuits of the computer system can interpret and execute. A Knowledge of the basic characteristics of machine language instructions is useful in understanding how a computer operates.
A machine language instruction is composed of: 1) An operation code; 2) Values indicating the number of characters to be processed by the instruction; 3) The addresses of the data to be used in the processing.
The operation code is a unique value which is typically stored in a single byte. This unique value indicates to the computer electronics what operation is to occur. For example, the letter of the alphabet “A” stored as the operation code might indicate that an addition operation is to occur. The letter “0” might mean that division is to take place.
The number of characters to be processed must be included in a computer instruction so that the electronic circuitry of the processor unit will reference the proper number of digits in the field to be processed. For example, if a four digit field were to be added to another four digit field, the number of characters specified in the instruction for each field would be four.
The locations of the fields involved in the operation must be specified in the instruction. This enables the circuitry to identify where in storage the data to be processed is located.
Although the formats of computer instructions vary a great deal between different computer systems, the basic elements of operation code, number of characters to process, and the addresses of the data to be processed will almost always be present.
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