Computers today. Гурьянова В.И. - 13 стр.

counter are often known as “jumps” and allow for loops (instructions that are re-
peated by the computer) and often conditional instruction execution.
       It is noticeable that the sequence of operations that the control unit goes
through to process an instruction is in itself like a short computer program – and
indeed, in some more complex CPU designs, there is another yet smaller com-
puter called a micro sequencer that runs a microcode program that causes all of
these events to happen.

                                 Arithmetic/logic unit (ALU)

       The ALU is capable of performing two classes of operations: arithmetic and
logic. The set of arithmetic operations that a particular ALU supports may be limited
to adding and subtracting or might include multiplying or dividing, trigonometry
functions (sine, cosine, etc) and square roots. Some can only operate on whole num-
bers (integers) whilst others use floating point to represent real numbers-albeit with
limited precision. However, any computer that is capable of performing just the sim-
plest operations can be programmed to break down the more complex operations
into simple steps that it can perform. Therefore, any computer can be programmed to
perform any arithmetic operation-although it will take more time to do so if its ALU
does not directly support the operation. An ALU may also compare numbers and re-
turn Boolean truth values (true or false) depending on whether one is equal to,
greater than or less than the other (“is 64 greater than 65?”).

                                            Memory

       A computer’s memory may be viewed as a list of cells into which num-
bers may be placed or read. Each cell has a numbered “address” and can store a
single number. The computer may be instructed to “put the number 123 into the
cell numbered 1357” or to “add the number that is in cell 1357 to the number
that is in cell 2468 and put the answer into cell 1595”. The information stored in
memory may represent practically anything. Letters, numbers, even computer
instructions may be placed into memory with equal ease. Since the CPU does
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