Central Processing Unit

Central Processing Unit

Central Processing Unit

• The CPU or Central Processing Unit is the "brain" of the computer, it is the 'compute' in computer.
•  Without the CPU, you have no computer.

• Computer CPU's (processors) are composed of thin layers of thousands of transistors. Transistors are tiny, nearly microscopic bits of material that will block electricity when the the electricity is only a weak charge, but will allow the electricity pass through when the electricity is strong enough.
• The transistors within the CPU transition from being a non-conductor (resist the electricity) to a conductor (they conduct electricity) when the electrical chage is strong enough.
• The material that CPU transistors are made of loses its resistence to electricity and becomes a conductor when the electricity gets strong enough.
• The ability of these materials (called semi-conductors) to transition from a non-conducting to a conducting state allows them to take two electrical inputs and produce a different output only when one or both inputs are switched on.
• A computer CPU is composed of millions (and soon billions) of transistors.
• Because CPU's are so small, they are often referred to as microprocessors.
• Modern CPU's are what are called 'integrated chips'.

• The idea behind an integrated chip is that several types of components are integrated into a single piece of silicon, such as one or more execution cores, arithmetic logic unit or 'floating point' processor, registers, instruction memory, cache memory and the input/output controller.
• Each transistor is a receives a set of inputs and produces output.
• When one or more of the inputs receive electricity, the combined charge changes the state of the transistor internally and you get a result out the other side.
• This simple effect of the transistor is what makes it possible for the computer to count and perform logical operations, all of which we callprocessing.

• A modern computer's CPU usually contains an execution core with two or more instruction pipelines, a data and address bus, a dedicated arithmetic logic unit (ALU, also called the math co-processor), and in some cases special high-speed memory for caching program instructions from RAM.
• The CPU's in most PC's and servers are general purpose integrated chips composed of several smaller dedicated-purpose components which together create the processing capabilities of the modern computer.

CPU Generations

• CPU manufacturers engineer new ways to do processing that requires some significant re-engineering of the current chip design.
• When they create this new design that changes the number of bits the chip can handle, or some other major way in which the chip performs its job, they are creating a new generation of processors.

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 
• 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 down.
• 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.

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 the theory goes that the higher the number of mega or gigahertz, the faster the processor.
• However comparing raw speeds is not always a good comparison between chips. Counting how many instructions are processed per second is a better measurement