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
The slot 1 processor is no longer being produced. Below are two photos of an AMD Athlon 64 FX socket 939
processor and one photo of a Pentium 4 Extreme Edition socket 775 processor. These are later model
processors than the slot 1. These processors look similar, but they do have some differences, including
the number of contact points, (or pins), that they have. Another difference in some of the newer processors
is that the level 2 cache memory is located directly on the CPU chip itself. Any cache memory located outside
of a CPU like this is called level 3 cache memory. The usage is still the same though. Level 1 cache memory
is still located closest to the core of the CPU and is still usually smaller and faster than the level 2
cache memory. Some of the newer processors even have level 3 cache memory located directly on the CPU itself.
Any cache memory located outside of a CPU like this is called level 4 cache memory. The first photo below
shows the front and back of a Pentium 4 Extreme Edition processor. It has level 3 cache memory located
directly on the CPU itself. The second photo below shows the front and back of an AMD Athlon 64 FX processor.
It has level 2 cache memory located directly on the CPU itself. The third photo below shows the AMD processor
installed on a motherboard with a heatsink and fan.