Structure and functional units of central processing unit (CPU)


A central processing unit (CPU) (core) is composed of registers, an arithmetic logic unit (ALU), a control unit and the data lines (buses) that enable communication with other components.

These components are generally further divided, for example, contains the control unit for a more efficient processing of instructions, the instruction pipeline with multiple stages usually, inter alia, the instruction decoder.

The ALU contains comparators and hardware multiplier. In addition, sometimes located primarily in modern microprocessors are much finer subdivided units that are flexible or assignable and repeatedly executed units that allow the simultaneous processing of several commands.

Often, the memory management unit and a (possibly multi-level) cache is integrated into today’s processors. In some instances an I/O unit is incorporated, often with at least one interrupt controller.

There are also specialized processing units, for example, a floating point unit, a unit for vector functions or for signal processing. In this aspect, the transitions to a microcontroller or system-on-a-chip interconnects the other components of a computer system in an integrated circuit.

Control or tail

The controller, also called tail, controls the execution of the instructions. It ensures that the machine instruction is decoded in the instruction register from the instruction decoder and executed by the arithmetic unit and the other components of the computing system.

The command decoder translates binary machine instructions using the command table (instruction table) into corresponding instructions (microcode), which activates the time needed for execution of the command circuits.

There are three main registers with very fast responsive processor internal memory:

The instruction register: It contains the machine instructions currently being executed.
The program counter: This register shows active instruction executions. A jump instruction loads the address of its jump destination here.

The status register: it shows through flags the status that is generated by other parts of the computing system, including the calculation and the tail in the execution of certain commands in order to evaluate subsequent commands. Example: result of an arithmetic or comparison operation results, etc. Zero ‘,’ minus. ‘

In RISC processors no command decoder is sometimes necessary – in some RISC processors interconnect the command bits, the corresponding ALU and register units directly. There is then no microcode.

It can also be replaced by a pipeline an explicit instruction register. Sometimes multiple commands are simultaneously in progress, then the order of execution can be re-sorted (out-of-order execution).

Arithmetic unit and register

The calculator performs the elementary operations of a processor. It consists firstly the arithmetic logic unit (ALU) and the working registers. It can perform both arithmetic (such as the addition of two numbers) and logical (such as AND or OR) operations.

Due to the complexity of modern processors, in which usually several arithmetic units with specialized functions are present, one also speaks generally of the plant operation .

The working registers can record data (as data registers) and depending on the processor type, also record addresses (as an address register). Most operations can be performed directly only with the values in the registers.

Therefore, they represent the first level of memory hierarchy. The performance of each processor depends on the properties and in particular the size and number of registers.

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