CPU Facts
When selecting a CPU, be aware that you will need to match the motherboard and the CPU.
Either select a CPU supported by the motherboard, or select a motherboard that will support the
processor you have chosen. The following table lists several considerations for choosing a
processor:
Feature
Description
Intel and AMD are the two producers of processors used in modern PCs. In
addition, Motorola produces the PowerPC processor for Macintosh
computers.
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Manufacturer
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Intel has a larger market share, but AMD processors are growing in
popularity.
The operating system must be written to be compatible with a given
processor instruction set. The Hardware Abstraction Layer (HAL)
provides the interface between the processor and the operating
system.
Both Intel and AMD processors work in PC systems and support
Windows software.
Processor performance and special features vary between models and
manufacturers.
For the last several years, processors were capable of processing 32-bits of
information at a time. Newer processors can process 64-bits of information.
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32-bit or 64-bit
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Original 64-bit processors from Intel could only run 64-bit
applications. This means that the operating system and all
applications had to be written specially for 64-bit systems.
AMD introduced a 64-bit processor that was capable of running both
32-bit and 64-bit applications. Later 64-bit processors from Intel were
also capable of running 32-bit applications.
Early 64-bit processors were largely used in servers. 64-bit
processors are now common in desktop systems.
The covering, or die, of the processor must match its corresponding socket or
slot on the motherboard. Common styles are:

Packaging

A Pin Grid Array (PGA) has a series of pins on the bottom in
concentric squares. Pentium chips add more pins by staggering the
pin configuration. These processors are installed into motherboard
sockets.
A Single Edge Connector (SEC) or Single Edge Contact Cartridge
(SECC) mounts the processor on a circuit board. The cartridge is then
inserted into a slot on the motherboard, much like an expansion card
is installed into an expansion bus.
Note: The processor packaging typically includes specifications for the
voltage levels. In most cases, all processors that use the same packaging have
the same voltage needs. There are, however, a few exceptions in older
processors. In this case, make sure that the motherboard supplies the correct
voltage for the CPU by setting jumpers or editing the CMOS.
The VRM is an electronic device that supplies the appropriate voltage to a
processor; thus allowing multiple processors with different voltage
Voltage Regulator requirements to be mounted on the same motherboard. A VRM can either be
Module (VRM)
an installable device controlled through the BIOS, or soldered directly to the
motherboard and controlled by the processor. Installable VRMs are more
common in dual processor and server systems.
Processors operate using an internal clock that is the same as, or is a multiple
of, the motherboard bus speed. The speed is represented in MHz and is also
referred to as the frequency.
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Speed
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You can purchase processors of the same type but with different
speed ratings.
When selecting a processor, make sure the motherboard supports the
processor speed by reading the motherboard documentation first.
Most motherboards automatically detect the processor speed. If not,
you might need to use jumpers or edit the CMOS to configure the
processor speed.
Cache is memory that the processor can access directly without using the
system RAM. There are three types of processor cache:


Cache

Level 1 cache is integrated on the processor die itself.
Level 2 cache is additional cache. Originally, Level 2 cache was on
the motherboard, but all new processors include level 2 cache on the
processor die as well.
Level 3 cache is additional cache beyond the level 2 cache. A few
processors (such as Xeon and Itanium) have level 3 cache on the
processor. Otherwise, level 3 cache is on the motherboard.
Note: As the amount of cache on the processor has increased, the amount of
cache used on the motherboard has decreased. Very few newer motherboards
include cache.
Process Size
The process size refers to the manufacturing process used to etch transistors
onto the silicon wafer that will become the CPU. A smaller process size
means smaller transistors, which translates into a smaller CPU die with more
transistors and less power consumption. Process size is expressed in microns
(such as .25 microns) or nanometers (90 nm which equals .09 microns).
Many processors include advanced instruction sets for improving certain
processing tasks. Examples of these instruction sets include:

Advanced
Instruction Sets

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MMX (Multimedia Extensions) includes instructions for sound and
video processing.
SSE and SSE2 are extensions of MMX.
3DNow! is an improvement to MMX on AMD processors. 3DNow!
is used primarily to improve video and multimedia applications.
In each case, software must be specially written to take advantage of the
advanced instruction sets.
Hyper-threading
Hyper-threading is a feature of some Intel processors that allows a single
processor to run threads in parallel, as opposed to the older and slower
technology of processing threads linearly.
One way to increase performance is to add more processors to a system. This
can be done by:

Multi-processors
and multi-core
processors

Purchasing a multi-processor motherboard and installing two (or
more) processors on the motherboard.
Purchasing a multi-core processor that has multiple processor cores
integrated into a single processor package. This solution requires less
power than a multi-processor system.
In either case, software must be written to take advantage of the multiple
processors.
Mobile CPUs are used in notebook computers where portability and mobility
Mobile processors are a concern. Special versions of processors are built to minimize power
consumption and the amount of heat generated.
Processors require some form of heat dissipation system to function properly.
Heat sink and fan Without a heat dissipation system, a processor will overheat and burn out in
less than a minute. Most modern CPUs require a heat sink and a fan.
Throttling is the process of modifying the operating characteristics of a
processor based on current conditions.

Throttling

Throttling is often used in mobile processors to change the operating
frequency to minimize power consumption and heat output.
Throttling can also be used in low memory conditions to slow down
the processing of I/O memory requests, processing one sequence at a
time in the order the request was received.