Vintage Computer Manuals Blog

Manipulating data in main computer storage

admin — Wed, 01 Sep 2010 12:31:32 +0000

Once data has been recorded in main computer storage, it can be referenced and manipulated. It can be moved to other locations in main computer storage, used in arithmetic operations, compared to other data in storage, or otherwise be processed to prepare the desired output information. This is possible because of the ability of the computer program to direct the electronic circuitry to extract data located at a specific address and use the data for processing.

In a Figure, a segment of the operations required to produce a printed report from data contained in punched cards is shown. Under control of the computer program, the data from the input record is read into main computer storage at a specific address. The fields in the input record area are then moved to the fields in the output area. The instructions causing this to happen will reference both the address of the input fields and the address of the output fields in main computer storage. The fields in the output record area are then written on the report.

The ability to address data stored in main computer storage and process it after it is addressed form the basis of the internal operations in a computer system.

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Use of main computer storage

admin — Sat, 28 Aug 2010 10:59:53 +0000

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.

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Executing Instructions on a computer

admin — Mon, 23 Aug 2010 18:32:27 +0000

The execution of an Instruction on the computer system involves the control unit of the CPU “fetching,” or obtaining, the instruction from main computer storage and placing the instruction in an instruction register. An instruction register is nothing more than a storage area within the control unit of the CPU which can store a single Instruction at a time.
The control unit will also fetch any data required for the execution of the Instruction and place the data in special “registers” which can be referenced by the arithmetic/logic unit of the CPU.
The arithmetic/logic unit of the CPU is then given control. It will per. form the actual execution of the instruction and store the answer in another register.
The control unit will then place the answer into main computer storage.

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The central processing unit

admin — Fri, 13 Aug 2010 20:56:30 +0000

Instructions stored in main computer storage control the operations which occur within the central processing unit. The central processing unit (CPU) is the heart of the computer system. It contains the electronic circuitry which actually causes processing to occur. The CPU interprets the instructions in a computer program, performs the calculations and the moving of data as specified by the program, and controls the input/output operations of the system.

The central processing unit, of course, is a part of the processor unit. The CPU consists of two major components: the arithmetic/logic unit and the control unit.

The arithmetic/logic unit contains the electronic circuitry necessary to perform arithmetic operations such as addition, subtraction, multiplication, and division. It also contains the circuitry required to perform logical operations such as comparing one number to another and indicating the results of that comparison.

The control unit directs and coordinates the entire computer system. Its tasks Include controlling the Input/output units, controlling the opera tions of the arithmetic/logic unit in the CPU, and transferring data to and from main computer storage.

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Computer instructions

admin — Wed, 11 Aug 2010 22:42:46 +0000

The 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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