Processing/internal Memory

To manipulate and store symbols, the computer must have a "brain" that can perform certain predetermined operations and "remember" information. This "brain" is the processing/internal memory unit of the computer and is made up of three parts: (1) the arithmetic-logic unit, where actual processing is carried out; (2) the control unit, which directs all of these operations; and (3) the inter­nal, or main, memory. The control unit and the arithmetic-logic unit together form the central processing unit (CPU) of the computer.

All three units use the computer chips discussed in Lesson 1. Recall that a chip is a tiny piece of silicon that packs many hundreds millions of electronic elements into a tiny area. These elements, called transistors, actually carry on the control and logic operations at over several million operations per second! A combination of transistors and circuits on a chip results in an integrated circuit that is the key to the power and speed of all computers today. Because the chip is so small, it must be attached to a carrier device with wire prongs. This plugs it into the main circuit board, which contains other chips for the CPU, the main memory, and the control of input, output, and sec­ondary storage devices.

A CPU chip, or microprocessor, contains the control unit and the arith­metic-logic unit. The control unit manages the processing of data into infor­mation and the arithmetic-logic unit (ALU) handles the actual processing by performing arithmetic and logic operations on the data. Mainframe computers will have thousands CPU chips, but a personal computer will usually have only one. Having multiple CPU chips enables the mainframe to run faster and handle the large volume of processing for which it is responsible.

To help you understand what is going on in the CPU with the control and arithmetic-logic units, think of these units as two clerks working inside the computer: the head clerk (the control unit) and the working clerk (the arith­metic-logic unit). The head clerk's job is to tell the working clerk what cal­culations and comparisons to do based on instructions from the keyboard. The working clerk can only add, subtract, or compare two data items and must be told by the head clerk specifically what to do. Since the head clerk cannot do these calculations or comparisons and the working clerk cannot understand instructions from the keyboard, the two clerks must work together.

To store the data internally, the head clerk uses a blackboard (the internal memory). While the working clerk can communicate only with the head clerk, the head clerk can communicate with the user through a bulletin board (the screen) on which results are posted. The head clerk also stores data and infor­mation in file cabinets (the secondary storage).

To carry out a task, the head clerk receives instructions over the phone (the keyboard) and looks up the meaning of these instructions in a reference manual (the software). After interpreting the instructions, the head clerk retrieves needed data from the blackboard (the internal memory) and sends these data, and instructions as to what should be done with them, to the working clerk for action. After carrying out the instructions, the working clerk returns the result of this operation to the head clerk, who writes it on the blackboard. The head clerk may send results to the filing cabinets or retrieve additional data from there. The head clerk may also post results on the bulletin board or send them out to be printed.

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Дата добавления: 2015-11-14