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. See if you can find the areas that fetch,
decode, and execute the instructions. Can you also find the level 1 cache areas that store information? The
pipelined floating point area, logic areas, and superscalar integer execution units area are part of
what? Did you guess the arithmetic/logic unit? If so, you're right!
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." The speed of a clock
is rated by how many beats per second it can accomplish. 1 billion beats per second is referred to as 1Ghz.
For every beat, (except the very first), a machine cycle is completed. 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!
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. Currently AMD is using the socket 939, socket 940, and socket 754 processors.
Pentium is using the socket 775 and socket 478 processors. All of 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.
As with the other levels of cache memory, the higher the level, the further away from the core of the CPU it
is located. The higher levels of cache memory also are usually larger and slower than the smaller levels.
The first photo below shows the front and back of a Pentium 4 Extreme Edition socket 775 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 socket 939 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.