CPU (processor)
The Central Processing Unit (CPU) is the heart of your computer. It performs
nearly all the actual computation that takes place as the computer is used. The
choice of a CPU will affect the ultimate speed of the computer more than any
other single component.
Before we can explain the differences between CPUs, you must first be familiar
with certain CPU properties.
Clock speed Clock speed, measured in Gigahertz (GHz), (or Megahertz (MHz);1
GHz = 1000 MHz) is the number of calculation cycles that your CPU can
perform per second. Therefore, a higher clock speed generally indicates a
faster processor. But not all CPUs perform an equal quantity of work per
cycle, meaning two CPUs at the same clock speed can potentially perform
at very different levels.
IPC IPC, or instructions per cycle, is the amount of work a CPU can do in a
cycle. With modern processors this number is an average.
Front side bus speed (FSB) Front side bus speed is the rate at which the
CPU communicates with the northbridge chipset component on your motherboard,
measured in MHz. A larger FSB value shows that your CPU is
able to communicate with other components on the motherboard (and
thus your system) faster.
Interface (Socket/Slot) CPUs plug into a socket on the motherboard. It is
very important that your CPU is a COMPLETE MATCH to your motherboard
CPU socket. Plugging a CPU into the wrong socket will never
work and will usually break either the CPU, the socket, or both.
Bit width Modern processors are either 32-bit or 64-bit (this is a simplification;
see http://en.wikipedia.org/wiki/64-bit for details). For our purposes
a processor can be called 64-bit if it will support running a 64-bit
operating system. The newer chips from Intel and AMD all support this
for most 64-bit OSs. If you have any doubts, check the support materials
for the 64-bit OS you are interested in running.
Hyper-threading (HT) Hyper-threading is an Intel technology which allows
a single core processor to simulate having two cores, giving a performance
boost when running several programs at once. It requires motherboards
and chipsets supporting Hyper-Threading technology. The advantages of
the Hyper-Threading technology have never been breathtaking and Intel
has gone back and forth on it’s support in multi-core processors.
Cache Cache is memory implemented directly on the CPU. Data which is being
used in computations is stored in the cache as much as possible and can be
retrieved from there much faster than the same data can be pulled through
the northbridge from main memory. Generally, the larger the cache, the
faster the system will run. Cache comes in (usually) three varieties, L1,
L2, and L3. L1 being the smallest and fastest, and L3 being the largest
and slowest. Usually only the L2 cache size will be shown, as L3 is rarely
used in processor design, and L1 will often stay the same size throughout
an entire processor product line.
Core The core of the CPU is the heart of the CPU. Often several cores will be
marketed under the same name, so look at what core you are buying. Its
a mistake to choose a processor based solely on its rated speed in hertz .
This number, while easy to understand, does not tell the whole story. The
number of cores and the way they communicate will have a big effect, as
will the fundamental architecture of the core or cores themselves.
Slower processors are generally preferred for overclocking, as they can often
achieve higher overclocking percentages. Retail CPU’s come in a package
containing a HSF (Heat Sink Fan), instructions, and a warranty, often 3 years.
OEM CPUs do not include these.
The current CPU speeds and advantages change frequently, so for up-to-date
comparisons, you may want to check a website that specializes in Hardware
reviews, such as Tom’s Hardware Guide or Anandtech. A current (as of 14
February 2006) beginner’s explanation can be found at Behardware.