Introduction:

• Registers - Registers are special storage locations located inside the CPU. The data contained here can be accessed much quicker than the data contained in other memory locations, such as the RAM (random-access memory) and the ROM (read-only memory). Registers in different parts of the CPU are used for different functions. In the control unit, the registers are used to store the computer's current instructions and the operands (this is merely a fancy term for data that is being operated on by the CPU). Meanwhile, the registers found in the ALU, called accumulators, are used to store the results of the arithmetic or logical operations.
• Address Bus - The address bus is a collection of wires connecting the CPU with main memory that is used to identify particular locations (addresses) in main memory. The width of the address bus (that is, the number of wires) determines how many unique memory locations can be addressed.
• Arithmetic/Logic Unit (ALU) - The ALU is the part of the CPU that does the actual computing and calculations sent to it by programs.
• Cache - Small memories on or close to the CPU chip can be made faster than the much larger main memory. Most CPUs since the 1980s have used one or more caches, and modern general-purpose CPUs inside personal computers may have as many as half a dozen, each specialized to a different part of the problem of executing programs. It is very similar to the concept of a browser cache that stores data from visited web sites making subsequent visits to those sites load faster.
• Hyperthreading - The Intel Pentium 4 introduced hyperthreading which allows each pipeline to run more than one thread at a time. This essentially tricks the system into thinking that there are 2 processors. Hyperthreading only works with operating systems and applications that support it.

• With the Pentium MMX processors, 57 multimedia specific instructions were added to increase multimedia performance and increased the L1 cache size to 32KB.
• The Pentium Pro added Dynamic Execution and increase L2 cache to 512KB.
• The Pentium II had integrated MMX technology and used a new Single Edge Contact Cartridge(SEC).
• The Pentium III provided increased processor speeds, a 100mhz front size bus speed and increased L2 cache to 512KB.
• The Celeron processors are less expensive but only have a 66mhz bus and 128KB L2 cache.
• The Pentium IV introduced a number of graphics enhancements. 2 versions were made - The first was a 423-pin PGA package with 256 KB L2 cache. The second version offers a 478-pin PGA package with 512 KB of L2 cache.
• Intel Xeon processors are higher-end and based on their Pentium II, III and IV counterparts.

Current Trends:
A few years ago, Intel was the first to introduce a 64-bit processor (Itanium II). Since that time, 64 bit processors have become the standard. Clock speeds hit a brick wall at around 4GHz a few years back which forced CPU manufacturers to find new ways to squeeze more performance out of their chips. Intel and AMD both released "dual core" processors that are essentially 2 processors in one. The Intel Pentium D was basically 2 Pentium 4 processors together with their own cache. AMD launched a similar product called the AMD Athlon 64 X2 processor, however, the L1 cache was shared by the processors. Shortly after, Intel abandoned their Pentium line of processors which gave way to the Intel Core series. Core processors come in "Solo" or "Duo" (dual core) versions. This line was followed by the Intel Core 2 architecture that comes in "Duo" or "Extreme" versions.

Installing a Processor:
Before installing (or buying) a processor, you should make sure that your motherboard supports it. It is also very important to make sure that your motherboard uses the same package as your processor. In other words, a socket 775 processor (shown left) will not fit into a 478 socket. If you try to force it, you will likely bend the metal pins sticking out of the bottom of the processor. Typically, installation is as easy as placing the CPU in the socket and pushing down on the locking lever attached to the motherboard which can be seen on the left side of the image to the left. This lever is located on the side of the socket. Most CPUs and sockets are keyed so that you place it in the correct spot.

Cooling:
CPUs get very hot and the faster the CPU, the hotter it will get.

This is why we need to attach a fan or newer cooling method such as a liquid cooling system. A typical cooling fan is pictured to the right. Before you install your fan, place a little bit of thermal compound on the top of the CPU. The fan will typically have clamps that lock onto the side of the socket on the motherboard. These can be difficult to install. Be patient and try not to damage your motherboard, especially when removing the fan. After securing the fan, you will need to plug in the power cable to the appropriate spot on your motherboard. See your motherboard manual for the location.

• Performance: The processor is probably the most important single determinant of system performance in the PC. While other components also play a key role in determining performance, the processor's capabilities dictate the maximum performance of a system. The other devices only allow the processor to reach its full potential.
• Software Support: Newer, faster processors enable the use of the latest software. In addition, new processors such as the Pentium with MMX Technology, enable the use of specialized software not usable on earlier machines.
• Reliability and Stability: The quality of the processor is one factor that determines how reliably your system will run. While most processors are very dependable, some are not. This also depends to some extent on the age of the processor and how much energy it consumes.
• Energy Consumption and Cooling: Originally processors consumed relatively little power compared to other system devices. Newer processors can consume a great deal of power. Power consumption has an impact on everything from cooling method selection to overall system reliability.
• Motherboard Support: The processor you decide to use in your system will be a major determining factor in what sort of chipset you must use, and hence what motherboard you buy. The motherboard in turn dictates many facets of your system's capabilities and performance.