With the advent of 2001, Intel introduced the Pentium 4 family of CPUs, that ranged from 1.3 to the 1.7 Gigahertz speed range, and work on a 400 Megahertz motherboard host speed.

This Pentium CPU chip plugs into the ZIF (Zero Insertion Force) Socket and the CPU itself is secured usually with a tension bar lever on the side of the ZIF socket. Not all motherboards use ZIF sockets. For example slot 1 motherboards and early 386 and some 486 motherboards do not use ZIF sockets for their CPUs. Shown below are a few listings of various CPU sizes and pin configuration as they evolved, pre Slot 1 circa:

The Central Processing Unit (CPU) is the brains of the computer which does all the processing of data and information.The CPU itself is internally divided into two main sub-sections:

i) Arithmetic Logic Unit (ALU) - The ALU is the section of the computer where the actual math and logic operations are performed under the direction of the control unit.

ii) Control Unit. - The control unit receives instructions from the program, decodes them and then generates signals to inform the ALU as to what operation has been requested. In addition, the control unit orchestrates the operation of all the other logical blocks by generating the proper timing and control signals necessary to complete the execution of the instructions.

Many times people speak of a microprocessor as the CPU. Others refer to the system's main unit as the CPU. In both cases, the terminology is faulty. In the early days of computers, the central processing unit was the area of the computer where logical and mathematical computations were carried out. It was usually composed of discrete circuits or devices.

Several microprocessor chips are on the market, each with its own unique architecture, capabilities, and instruction set (operations that it can execute). The capabilities of the microprocessor used in a particular computer ultimately determine the characteristics and capabilities of the entire computer. Basically, microprocessors are classified by the size of their internal data storage registers. Common microprocessor sizes are 8 bits, 16 bits, 32 bits

• The operation of all microprocessors is basically the same. They all execute programs in a cyclic manner. An instruction cycle is followed by and execution cycle. These two cycles are repeated until the program is terminated, or until it reaches its end. During the instruction cycle, the processor retrieves an instruction from the memory, decodes it, and prepares to carry out the instructions from memory, decodes it, and prepares to carry out the instruction as directed. The instruction may call for addition data to be retrieved from memory, manipulated in a logical manner, or to be written into a memory location. In any case, the instruction is carried out during the processor's execution cycle.
• After completing the operations required by the instruction, the microprocessor moves sequentially to the next instruction. A particular instruction may cause the system to jump to another memory location to recieve another instruction. This instruction jump can be dictated directly by the instruction, or it can be based on the outcome of some logical operation.
• All microprocessors have a fixed set of operations they can perform. The operations that a given microprocessor can perform are referrred to as its instruction set. The size of the instruction set determines how many different operations the microprocessor can perform. This, in turn, determines how quickly data can be processed.

		Place the CPU into the CPU slot. Force down with moderate pressure until the CPU locks into place. Celeron processors should be locked into place with CPU locks which come with the motherboard. AMD CPUs require special care (see below)
		Socket CPUs are square with numerous pins. Upon observing the side with the pins one notices that a corner is blunted and differs from the other three. This corner is often marked and must be installed to the socket accordingly. Do not bend the pins!
		Place the CPU carefully in the socket motherboard ensuring that the blunted corner is properly placed onto the CPU socket. Be careful not to force the CPU down when there seems to be significant resistance against the applied pressure. This usually means a misplacement between the pins and the sockets which can lead to serious CPU damage.
		Make sure that you install a CPU fan with your processor. Heat is the number one enemy of CPUs. Today's performance processors run extremely hot, if proper cooling is not provided, damage to the CPU and other parts of your system could result.
It is crucially important that your CPU is properly cooled, due to the high temperature and heat produced by the core voltage of the cpu internally. There are many good quality fans on the market now to alleviate this heating problem. With early Pentium processors (Pentium 66 to 75), this heat problem was especially acute, due to the internal voltage of the cpu not being stepped down. The first fan with the copper heatsink is designed for a 486 CPU The second and third fans are for midrange Pentiums - Pre slot 1 CPUs The last fan is designed for a Pentium II - CPU that works with a slot 1 motherboard.