Pictured here is a typical CPU chip (known as a socket-7 chip). The actual size of the chip itself is about 2 centimetres square. the rest of the module consist of a plastic case and, pins which connect it to the computer. Some newer models of chips include an external cache in the case as well. It's hard to see at this detail level, but the CPU is made up primarily of transistors. These transistors are grouped into gates which do very simple operations on data bits. These gates are grouped into larger logical units which do useful functions.
The main parts of the CPU are: Control - Decides which operation is being performed. It sends signals to the various multiplexors to decide which output occurs. This peice examines the actual machine instruction code. Registers - Small local storage areas, used to store data about to be manipulated. These vary in size and number depending on the processor. Once 16 bit, now commonly 32 bit, and in the future 64 bit will become more common. They can store numerical values or other data including memory addresses and machine-language instructions. Arithmetic Logic Unit (ALU) - Performs all mathematical operations, such as addition, subtraction, multiplication, division, logical bit shifting. Multiplexors - Select input or output from a number of possible values. These are used to decide input and output in the CPU. Cache - Not always present, but can enhance CPU performance by storing regularly-used values for fast retrieval.
One of the most important sections of the CPU is the Arithmetic Logic Unit, or ALU. This component can do many operations including addition, subtraction, multiplication, and other bit-altering routines like logical AND and OR. Like all main sections of the CPU there are many control lines running to and from the ALU, as well as input and output.
The CPU decides what should be done next by reading instructions from the computer's memory. These instructions are created by a programmer, usually using a high-level language like C, C++, or JAVA. When a high-level program is compiled, it is translated into machine-language instructions. These are in binary format but can be represented by what is called "Assembly language". Essentially this is just the binary instructions translated into human-understandable words.
Comparing CPUs is at the same time difficult and simple. There are a number of ways to evaluate CPU performance. Unfortunately few are very straightforward or accurate. The simplest comparison with which everyone is familar is Clock Speed, usually expressed in Mega-Hertz (MHz). This represents directly the number of calculations per second that the processor can perform.
Not too long ago (March, 2000) the 1 GHz (1 Giga-Hertz = 1000 Mega-Hertz) barrier was broken by two leading chip manufacturing companies, Intel and AMD. In at least one benchmarking test, the Intel Pentium III chip out-did the AMD Athlon by a very small margin. The difference was simply due to materials used to manufacture the chip.
These new CPUs will not work in any computer, so don't go and buy a brand new PIII 1G chip to replace your old 486 chip. Only certain motherboards can accept certain types of chips. The size and shape of the chip itself can vary from model to model. The first chip shown above will fit into a regular pentium slot, know as Socket 7. The next one shown, at the top of this section, is a brand-new Intel Pentium III 1GHz processor. As you can see by the shape and size, this new chip attaches to the motherboard in a completely different way than the Socket 7. Even if the sockets were the same for both chips, the older motherboard could probably not provide enough electricity, or fast enough clock signals to the new chip to make it work.
from: http://www.cs.usask.ca
