CPU and Main Memory

The CPU, for central processing unit, follows the instructions of the soft­ware to manipulate data into information. The CPU consists of two parts: (1) the control unit and 21 the arithmetic/logic unit. The two components are connected by a kind of electronic "roadway" called a bus.

The control unit tells the rest of the computer system how to carry out a program's instructions. It directs the movement of elec­tronic signals between main memory and the arithmetic/logic unit. It also directs these electronic signals between main memory and the input and output devices.

The arithmetic/logic unit, or ALU, performs arithmetic operations and logical operations and controls the speed of those operations.

As you might guess, arithmetic operations are the fundamental math operations: addition, subtraction, multiplication, and division.

Logical operations arc comparisons. That is, the ALU compares two pieces of data to see whether one is equal to ( = ), greater than (>), or less I than (<) the other. (The comparisons can also be combined, as in "greater than or equal to" and "less than or equal to.")

Main Memory

Main memory—variously known as memory, primary storage, internal memory, or RAM (for random access memory)—is working storage. It has three tasks. (1) It holds data for processing. (2) It holds instructions (the pro­grams) for processing the data. (3) It holds processed data (that is, informa­tion) waiting to be sent to an output or secondary-storage device. Main memory is contained on special microchips called RAM chips, as we describe in a few pages. This memory is in effect the computer's short-term capacity. It determines the total size of the programs and data files it can work on at; any given moment.

Date: 2015-04-20; view: 897