What is a Microprocessor

A microprocessor is a computer processor on a microchip. It's sometimes called a logic chip. It is the "engine" that goes into motion when you turn your computer on. A microprocessor is designed to perform arithmetic and logic operations that make use of small number-holding areas called registers. Typical microprocessor operations include adding, subtracting, comparing two numbers, and fetching numbers from one area to another. These operations are the result of a set of instructions that are part of the microprocessor design. When the computer is turned on, the microprocessor is designed to get the first instruction from the basic input/output system (BIOS) that comes with the computer as part of its memory. After that, either the BIOS, or the operating system that BIOS loads into computer memory, or an application program is "driving" the microprocessor, giving it instructions to perform.

The first microprocessor was the Intel 4004, introduced in 1971. The 4004 was not very powerful -- all it could do was add and subtract, and it could only do that 4 bits at a time. But it was amazing that everything was on one chip. Prior to the 4004, engineers built computers either from collections of chips or from discrete components (transistors wired one at a time). The 4004 powered one of the first portable electronic calculators.

The first microprocessor to make it into a home computer was the Intel 8080, a complete 8-bit computer on one chip, introduced in 1974. The first microprocessor to make a real splash in the market was the Intel 8088, introduced in 1979 and incorporated into the IBM PC (which first appeared around 1982). If you are familiar with the PC market and its history, you know that the PC market moved from the 8088 to the 80286 to the 80386 to the 80486 to the Pentium to the Pentium II to the Pentium III to the Pentium 4. All of these microprocessors are made by Intel and all of them are improvements on the basic design of the 8088. The Pentium 4 can execute any piece of code that ran on the original 8088, but it does it about 5,000 times faster!

The following table helps you to understand the differences between the different processors that Intel has introduced over the years.

• The date is the year that the processor was first introduced. Many processors are re-introduced at higher clock speeds for many years after the original release date.
• Transistors is the number of transistors on the chip. You can see that the number of transistors on a single chip has risen steadily over the years.
• Microns is the width, in microns, of the smallest wire on the chip. For comparison, a human hair is 100 microns thick. As the feature size on the chip goes down, the number of transistors rises.
• Clock speed is the maximum rate that the chip can be clocked at. Clock speed will make more sense in the next section.
• Data Width is the width of the ALU. An 8-bit ALU can add/subtract/multiply/etc. two 8-bit numbers, while a 32-bit ALU can manipulate 32-bit numbers. An 8-bit ALU would have to execute four instructions to add two 32-bit numbers, while a 32-bit ALU can do it in one instruction. In many cases, the external data bus is the same width as the ALU, but not always. The 8088 had a 16-bit ALU and an 8-bit bus, while the modern Pentiums fetch data 64 bits at a time for their 32-bit ALUs.
• MIPS stands for "millions of instructions per second" and is a rough measure of the performance of a CPU. Modern CPUs can do so many different things that MIPS ratings lose a lot of their meaning, but you can get a general sense of the relative power of the CPUs from this column.

From this table you can see that, in general, there is a relationship between clock speed and MIPS. The maximum clock speed is a function of the manufacturing process and delays within the chip. There is also a relationship between the number of transistors and MIPS. For example, the 8088 clocked at 5 MHz but only executed at 0.33 MIPS (about one instruction per 15 clock cycles). Modern processors can often execute at a rate of two instructions per clock cycle.

There are many microprocessors available to the public and there are three basic characteristics that differentiate microprocessors:

1. Instruction set: The set of instructions that the microprocessor can execute.
2. bandwidth : The number of bits processed in a single instruction.
3. clock speed : Given in megahertz (MHz), the clock speed determines how many instructions per second the processor can execute.

In the case of either bandwidth or clock speed, the higher the value, the more powerful the CPU. For example, a 32-bit microprocessor that runs at 50MHz is more powerful than a 16-bit microprocessor that runs at 25MHz.

In addition to bandwidth and clock speed, microprocessors are classified as being either RISC (reduced instruction set computer) or CISC (complex instruction set computer).

Below is a chart that compares and contrasts important features found on some of the more popular chips in the market today.

	Transistors	CPU Speed	L2 Cache	Front-Side Bus Speed
Celeron	7,500,000	1.06 GHz - 2 GHz	256 KB, full speed	133 MHz and 400 MHz
Pentium II	7,500,000	233 MHz - 450 MHz	512 KB, half speed	100 MHz
Pentium III	9,500,000	450 MHz - 1 GHz	256 KB, full speed	133 MHz
Pentium III Xeon	28,100,000	500 MHz - 1 GHz	256 KB - 2 MB, full speed	100 MHz
Pentium 4	55,000,000	1.4 GHz - 3.4 GHz	256 KB, full speed	800 MHz
K6-II	9,300,000	500 MHz - 550 MHz	N/A	100 MHz
K6-III	21,300,000	400 MHz - 450 MHz	256 KB, full speed	100 MHz
Athlon (K7)	22,000,000	850 MHz - 1.2 GHz	256 KB, full speed	200 MHz and 266 MHz
Athlon XP	37,500,000	1.67 GHz	384 KB, full speed	266 MHz
Duron	N/A	700-800 MHz	64 KB, full speed	200 MHz
PowerPC G3	6,500,000	233 MHz - 333 MHz	512 KB, 1 MB, half speed	100 MHz
PowerPC G4	10,500,000	400 MHz - 800 MHz	1 MB, half speed	100 MHz
Athlon 64	105,900,000	800 MHz	1 MB, half speed	1.6 GHz
G5	58,000,000	2.5GHz	512 KB	900MHz - 1.25GHz

Microprocessors used in the MAC

Further Information

• For more in-depth technical specifications on these chips, visit SandPile.org.
• Also, check out HardwareCentral's CPU section for articles, opinions, reports, and tutorials.
• If you're looking to buy a CPU and want to know where to get the absolute best price, visit SharkyExtreme's Weekly CPU Price Update. Page contains prices and vendors for almost every PC CPU on the market today.

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