This part of the computer's CPU or microprocessor performs mathematical and logical tasks. Data from memory storage comes here and goes to memory storage again and again until it is fully processed. During this cycle the functions of the microprocessor can be divided into a number of small operations or micro operations. The time it takes for a basic operation to be completed is called 'machine cycle time'. This time is usually measured in nanoseconds ( nano second = 1 part of 100th part of 1 second). The frequency of the machine cycle (i.e., the rate of cycles per second) caused by the timing circuit located inside the microprocessor is expressed in MHz . MHz is the number of million machine cycles per second. For example, 10 MHz means 10 million cycles per second. Modern personal computers typically run from 10 MHz to 33 MHz. This shows how fast a modern computer can work. ALU is also responsible for moving and transferring data. This part can do simple logical functions like 'and' or 'no'. This unit uses yag , bieg , multiplication , division, to check whether a number is positive or negative or the number is zero , or whether one number is smaller , larger or equal to the other. And from this the computer can take the right step or reach a logical conclusion by checking the many conditions of processing.