Hardware components of the PC
The CPU
What happens inside a Microprocessor?

The block diagram above shows a simplified version of the Pentium processor and the blocks shown represent:

• Core - This is the heart of the Pentium, the execution unit that carries out the processing. The Pentium has two Arithmetic Logic Units (ALU) that are fed by individual pipelines, allowing it to interpret and carry out two instructions per clock cycle.
• Instruction and Pre-Fetch Unit - The Instruction decoder is a set of logic gates which take a binary number, which represents an instruction, and sets up the the various areas of the processor to carry out the instruction. The Pre-Fetch Unit is used to fetch the next list of instructions to be carried out from the Code Cache. As the instructions are stored on the processor chip they are executed very quickly. If this were not so each instruction would have to be loaded individually from memory and carried out before the next could be loaded, a process carried out by some of the earlier processors.
• Integer ALU - This is the section that carries out the required calculations on whole numbers (integers).
• Registers - These are small areas of memory that hold interim and final results of the calculations.
• Floating Point Unit - The ALU only works on integers, any non-integer calculations take place here.
• Branch Predictor - In a list of instructions there are usually conditional branches. A branch is where the program will continue with different instruction depending on the resultant value of the instruction previous to the branch instruction. As the Pentium brings in several instructions and holds them in Pre-fetch Unit this may well include the branch and the instructions that follow it. As it is not known at this time which set of instructions is going to be executed, the Branch Predictor predicts which and loads a set of instructions accordingly. If it has got it wrong then the incorrect set of instructions are discarded and the correct set loaded. It is hoped that the predictor will get it right more times than it gets it wrong.
• Primary Cache¹ - this is called the level 1 cache, a lot of instructions are loaded at a time, which are stored here The instructions and data are separated into two individual caches.
• Bus Interface - This brings the instructions and data into the processor and separates them for it to use. It also recombines them and sends them out after processing has been carried out. 

The processor clock keeps all the different parts of the processor in step. Each tick of the clock causes something to happen within the blocks of the processor. If the clock is running at 200MHz it means that there are 200,000,000 ticks. The speed of a processor is generally given in millions of instructions per second (mips). 
The Pentium processor has 3.3 million transistors and runs at 100,000,000 mips. The processor keeps track of where it is by using a Program Counter (PC), one of the registers. The program counter holds the internal memory location of the next instruction to be executed. When an instruction’s time comes for it to be executed it is loaded into the Instruction Register (IR). At the same time as the instruction is being executed the program counter is incremented to the next memory location. If the instruction is a branch then the program counter is loaded with the value of the memory location given as a result of the calculations of the branch e.g. if the branch instruction said " jump location 3254" - ‘3254’ would be placed in the program counter and the next instruction pulled from there. The Arithmetic Logic Unit (ALU) works in conjunction with the general registers as temporary storage, sometimes one or two of these are commonly called Accumulators. There is also a Status Register (SR), which uses each individual bit to give the status of something, e.g a zero result, an overflow, a carry etc. The control unit uses these to execute a conditional instruction such as "If the result of the calculation is zero then jump to memory location 6534".

[1] For more on Cache,  click here