CPU - Central Processing Unit

CPU - Central Processing Unit

Definition of CPU

• CPU - “Central Processing Unit”, is the brains of the computer. Sometimes referred to simply as the processor or central processor.
• Computer CPU's (processors) are composed of thin layers of thousands of transistors
•  The CPU is where most calculations take place.
• In terms of computing power, the CPU is the most important element of a computer system.
• On large machines, CPUs require one or more printed circuit boards. On personal computers and small workstations, the CPU is housed in a single chip called a microprocessor.
• Two typical components of a CPU are: The arithmetic logic unit (ALU), which performs arithmetic and logical operations.
• The control unit, which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary.

CPU Components

A lot of components go into building a modern computer processor and just what goes in changes with every generation as engineers and scientists find new, more efficient ways to do old tasks.

1. Execution Core(s)
2. Data Bus
3. Address Bus
4. Math Co-processor
5. Instruction sets / Microcode
6. Multimedia extensions
7. Registers
8. Flags
9. Pipelining
10. Memory Controller
11. Cache Memory (L1, L2 and L3)
12. Measuring Speed: Bits, Cycles and Execution Cores

CPU Bit Width

• The first way of describing a processor is to say how many bits it processes in a single instruction or transports across the processor's internal bus in a single cycle (not exactly correct, but close enough). 
• The number of bits used in the CPU's instructions and registers and how many bits the buses can transfer simultaneously is usually expressed in multiples of 8 bits. 
• It is possible for the registers and the bus to have different sizes. 
• Current chip designs are 64 bit chips.
• More bits usually means more processing capability and more speed.

CPU Clock Cycles

• The second way of describing a processor is to say how many cycles per second the chip operates at.
• This is how many times per second a charge of electricity passes through the chip. The more cycles, the faster the processor.
• Currently, chips operate in the billions of cycles per second range.
• More clock cycles usually means more processing capability and more speed.

CPU Execution Cores

• The third way of describing a processor is to say how many execution cores are in the chip.
• The most advanced chips today have eight execution cores.
• More execution cores means you can get more work done at the same time, but it doesn't necessarily mean a single program will run faster.
• To put it another way, a processor with one execution core might be able to run your MP3 music, your web browser, a graphics program and that's about where it starts to slow down enough, it's not worth it running more programs.
• A system with a processor with 8 cores could run all that plus ten more applications without even seeming to slow .
• More execution cores means more processing capability, but not necessarily more speed.
• The most advanced processors available are 64-bit processors with 8 cores, running as fast as 3-4 gigahertz. Intel has released quad-core 64-bit chips as has AMD.

Multi-Processor (Multi-CPU) Computers

The biggest supercomputers are running hundreds of thousands of quad-core processors in parallel to do major calculations for such applications as thermonuclear weapons simulations, radioactive decay simulations, weather simulations, high energy physics calculations and more.

CPU Speed Measurements

The main measurement quoted by manufacturers as a supposed indication of processing speed, is the clock speed of the chip measured in hertz. The theory goes that the higher the number of mega or gigahertz, the faster the processor.

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