How CPU Enforcement presenter
Let us examine how the central processing unit, combined with the memory, make a computer program. We will look at how just a program guide is executed. In fact, most of today's computers can perform only one command at a time, although they do it quickly. Multiple PCs can execute instructions in less than a millionth of a second, while the speed demon called supercomputers can execute instructions in less than a billionth of a second.
Before an order can be made, the program instructions and data to be placed into memory from an input device or a secondary storage device (this process is complicated by the fact that, as we said earlier, the data will be able to make a temporary stop in a register).
As Figure 2 shows, once the data and instructions needed in memory, the central processing unit perform the following four steps for each command: Controller load (be) instructions from memory.
Decoding controller command (to decide what it means) and directs that the necessary data is transferred from memory to the arithmetic unit / logic. The first two steps together are called instructional time, or I-time.
The unit arithmetic / logic perform arithmetic or logical instructions. That is, the ALU is given control and perform the actual operation on the data.
Thc unit arithmetic / logic stores the results of this operation in memory or in registers. Step 3 and 4 together called execution time, or E-time.
The last control unit to direct the memory to release the results to an output device or a secondary storage device. The combination of me time and time E-called machine cycle. Figure 3 shows a guide to go through the machine cycle.
Each central processing unit has an internal clock that generates pulses with a fixed rate to synchronize all computer activity. A single cycle instruction machine can be made up of a significant number of extra instructions, each of which would take at least a clock cycle. Each type of central processing unit is designed to understand a specific group of instructions called scripts. Just as there are many different languages that people understand, so each different type of CPU has an instruction set it out. Therefore, a CPU such as a Compaq personal computer can not understand the instructions from a CPU-say, for a Macintosh computer.
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