CENTRAL PROCESSING UNIT (CPU)

The heart of any computer system is the Central Processing Unit (CPU) which consists of storage, Arithmetic and Logic Unit, and control elements.

CENTRAL PROCESSING UNIT
Fig. 1.15: CENTRAL PROCESSING UNIT

PRIMARY STORAGE SECTION (MAIN MEMORY OF RAM)

The primary storage also called as (main memory) section is used for four purposes. Three of these relate to the data being processed.

  • Data is fed into an input storage area where it is held until ready to be processed.
  • A working storage space that is like a sheet of scratch paper is used to hold the data being processed and the intermediate results of such processing.
  • An output storage area holds the finished results of the processing operations until they can be released.
  • In addition to these data-related purposes, the primary storage section also contains a program storage area that holds the processing instructions.

The separate areas used for these four purposes are not fixed by built-in physical boundaries in the storage section. Rather they can vary from one application, output result in another processing and instruction in a third. The person writing the application instructions determines how the space will be used for each job.

THE ARITHMATIC AND LOGIC UNIT (ALU)

The arithmetic logic and control sections together make up the central processing unit (CPU). All calculations are performed and all comparison (decisions) is made in the arithmetic-logic section of the CPU. Once data is fed into primary storage from the input device, they are held and transferred as needed to the arithmetic-logic place in primary storage.

Intermediate results generated in the arithmetic-logic unit are temporarily placed in a designated working storage area until needed at a later time. Data may thus move from primary storage to the arithmetic-logic and back again to storage many times before the processing is completed. Once completed the final results are released to an output storage section and from there to an output device.

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