Microprocessor

The microprocessor, (or CPU), is the brain of the computer. The picture above shows a slot 1 processor with heatsinks and a fan, which prevent it from overheating. Below is the processor without the heatsinks and fan, being inserted into a slot 1 motherboard connection. Slot 1 processors have the microprocessor and level 2 cache memory mounted on a circuit board, (or card), which is enclosed inside of a protective shell.

The enclosed slot 1 processor card contains the central processing unit, (or CPU), with its level 1 cache memory. The central processing unit also contains the control unit and the arithmetic/logic unit, both working together as a team to process the computer's commands. The control unit controls the flow of events inside the processor. It fetches instructions from memory and decodes them into commands that the computer can understand. The arithmetic/logic unit handles all of the math calculations and logical comparisons. It takes the commands from the control unit and executes them, storing the results back into memory. These 4 steps, (fetch, decode, execute, and store), are what's called the "machine cycle" of a computer. These 4 basic steps are how the computer runs each and every program. The microprocessor's level 1 cache memory, is memory that is contained within the CPU itself. It stores the most frequently used instructions and data. The CPU can access the cache memory much faster than having to access the RAM, (or Random Access Memory). Below is a picture of what's inside of a Pentium 3 processor. The control unit, arithmetic/logic unit, and level 1 cache are contained within the center CPU chip. Level 2 cache memory is visible on the right-hand side of the processor card.

Level 1 cache memory is memory that is included inside of the CPU itself. It is usually smaller and faster than level 2 cache memory. Level 2 cache memory is memory between the RAM and CPU. It is used when the level 1 cache memory is full or is too small to hold the intended data. Originally it was not directly on the CPU chip itself. *Read the update at the bottom of this page.* The photo above shows level 2 cache memory on the processor card, beside the CPU. Below are two photos of a CPU. The photo on the bottom is a view of the CPU chip from the outside. The photo on the top is a large map of the inside of the CPU, showing the different areas and what their function is.

At the top you can also see the clock driver. The clock driver is what times, or sets the pace, for the computer. The clock's speed, is how CPUs are rated. Each machine cycle consists of two beats. Each beat the control unit fetches and decodes data, which is called the "instruction cycle." At the same time the arithmetic/logic unit executes and stores data, which is called the "execution cycle." Common CPUs available today perform at 3Ghz and faster. This means that a 3Ghz CPU can execute 3,000,000,000 instructions in a single second!