CONTROL PROCESSING UNIT

Introduction:

CPU stands for Central processing unit. It is also known as microprocessor or processor.

A CPU is brain of a computer. It is responsible for all functions and processes.

Regarding computing power, the CPU is the most important element of a computer system.

The CPU is consisted of thin layers of thousands of transistors.

Each transistor receives a set of inputs and produces output.

The Central Processing Unit (CPU) performs the actual processing of data.

The data it processes is obtained, via the system bus, from the main memory. Results from the CPU are then sent back to main memory via the system bus.

The CPU has two main components, these are:

  • Arithmetic Logical Unit

 

  • Control Unit

 

  • Registers

 

Arithmetic Logical Unit:

§  The ALU is the part of a CPU that performs all arithmetic computations including addition, subtraction, multiplication, and division.

§  The Arithmetic Logic Unit also performs all logical operations.

§  The ALU is the fundamental building block of the CPU.

§  In some CPUs an individual ALU is further divided into two units called an Arithmetic Unit (AU) and a Logic Unit (LU).

§  Normally the ALU has direct input and output access to the processor controller, main system memory (RAM), and input/output devices.

Control Unit:

§  The CPUs control unit is responsible for executing or storing the results coming out of the ALU.

§  Within the CPU, the control unit performs the functions of fetch, decode, execute, and store.

§  The control unit communicates with both the arithmetic logic unit (ALU) and memory, and literally directs the entire computer system to carry out, or execute, stored program instructions.

§  Basically a control unit fetches or retrieves an instruction from memory and then analyzes the instruction it fetched before deciding how it should be processed.

§  Depending on the action required, the control unit will then send segments of the original instruction to the appropriate section of the processor.

Registers:

§  Registers are temporary storage areas which are responsible for holding the data that is to be processed.

§  They store the instructions and data in a processor. This data is further used by Control Unit.

§  There are some registers used for specific tasks such as program counter, stack, and flags etc.

§  Registers work under the direction of the control unit to accept, hold and transfer instructions or data and perform arithmetic or logical comparisons at a high rate of speed.

The Components of CPU from purchasing point.

  • Clock Speed

 

  • Cores

 

  • Cache

 

Control Unit:

§  A CPUs clock speed is a frequency that is measured in hertz.

§  For example, you may see a processor’s speed measured in megahertz (MHz) or gigahertz (GHz).

§  A modern processors clock speed is rated in gigahertz.

§  The clock speed actually used to be the main determining factor of how fast a processor is, and generally a faster clock speed equalled better performance.

Cores:

§  A multi-core processor is a processing system composed of two or more independent processing cores.

§  More cores allow computer systems to be more responsive while multi-tasking and multiple cores also help numerous applications specifically coded for multiple core processors to perform much faster.

§  When shopping for a computer look for a processor that contains the most cores, especially if you are a power user or into digital media applications, you may just notice a big performance increase.

§  Many digital media apps like Adobe Photoshop, Adobe Premiere Pro, and others will benefit from multiple processing cores.

Cache:

§  Cache is very important processor feature that you should pay attention to when shopping for a modern CPU for it can dramatically speed up the performance of a processor.

§  Cache acts as a buffer between your RAM and the CPU to speed up the processors internal processing engine.

§  Cache is essentially a super fast memory technology that resides on the CPU.

§  It holds recently accessed or pre-fetched instructions so the processor can grab them quickly to operate more efficiently.

§  Pulling data and instructions from the systems RAM in comparison takes much longer than pulling it from a cache.

§  When selecting a processor, a larger cache size as well as multiple levels of cache will improve overall CPU performance.

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