Difference Between CPU And ALU And CU
Central processing unit (CPU)
The central processing unit, or CPU, consists of the arithmetic/logic unit (ALU) and the control unit. The CPU is closely associated with the internal memory. The instructions that guide the CPU and the data that it processes all come from memory. During processing, the CPU may receive and send data from memory thousands or millions of times per second.
Arithmetic/Logic Unit (ALU).
The computer’s ability to perform numerical and logical operations is provided by the ALU. All of the ALU’s operations—even its logical operations—are performed using binary digits. Binary numbers can be added, subtracted, multiplied, and divided in much the same manner as conventional decimal numbers. To simplify the design of computer circuits, however, various ways have been worked out to perform all arithmetic operations by means of addition techniques. Even highly complicated integral or differential calculus procedures are carried out by repeated use of such simple techniques. Logical operations can be performed with binary digits by letting the digits stand for “true” and “false” instead of for the numbers 1 and 0.
The ALU is divided into different sections for different functions, such as adding numbers, comparing numbers, and performing various logical functions. One very important kind of section is known as a register. All registers store bits of information that are received in the form of electron pulses. Then, at the CPU’s command, they release the information for use elsewhere. Some registers can do other jobs—such as decoding instructions—in addition to storing information temporarily.
Registers usually consist of banks of electronic switches known as flip-flops. A typical flip-flop is made up of a pair of transistors connected in such a way that an electron pulse makes them switch states. When the incoming pulse makes one transistor flip on, the other flips off and at the same time releases an outgoing pulse. Many flip-flops can be connected together to make registers for counting or for other functions.
The control unit schedules and coordinates the work of all of the other parts of the computer. It sees to it that program instructions are carried out in the proper sequence, that output intended for the printer actually goes to the printer and not to one of the disk drives, that information meant to be stored in RAM is not displayed on the screen instead, and that countless other such jobs are done efficiently and correctly.
One of the main functions of the control unit is to regulate the speed of computer operations so that the operations can be synchronized. To do this, it sends out a continuous stream of electronic pulses generated by an oscillator called the clock. The clock sets the basic rhythm of all of the CPU’s calculating and processing operations. Pulses generated anywhere in the CPU are synchronized to the clock “beat” so that operations take place in exactly the right order.
Different kinds of computers have different clock speeds. Most PCs have clock speeds of around 3 to 4 GHz (gigahertz, or billions of cycles per second). In general, the faster the clock speed of a processor, the faster the computer can perform its functions. However, employing more than one processor in a computer or using processors with multiple cores can achieve even higher processing speeds.