Processor Types: A First Look

So many types of computer processors, also referred to as microprocessors, are on the market today that it can be quite confusing to wade through them all. All processors are not created equal, and each processor has its own characteristics that make it unique. For instance, a processor that is built around an architecture common to other processors of the same time period may actually operate at double or triple the speed. Fierce competition among the various chip makers lays the groundwork for new technological innovations and constant improvements.

Central Processing Unit (CPU)

The microprocessor, or brain, of the computer. It uses logic to perform mathematical operations that are used in the manipulation of data.

The most obvious difference among processors is the physical appearance of the chips, meaning that many processors differ noticeably from one another in size and shape. The first processor that Intel released was packaged in a small chip that contained two rows of 20 pins each. As processor technology improved, the shape and packaging scheme of the processor also changed. Modern processors, such as the Intel Pentium 4 class processors, use an advanced packaging scheme in which the processor is encased in a single-edge cartridge (SEC) module that plugs into a slot on the motherboard. Much like an expansion card that easily plugs into the motherboard, the SEC module can easily be removed and upgraded. This design also reduces the cost involved in producing the CPU.

Complex Instruction Set Computing (CISC)

A full complement of instructions used by a processor to complete tasks such as mathematical calculations. Used in the most common type of processors produced; Intel processors are currently based on this standard.

Reduced Instruction Set Computing (RISC)

A reduced set of instructions used by a processor. PowerPC and Alpha processors are manufactured using this standard. The reduced instruction set enables a microprocessor to operate at higher speeds.

microcode

The smallest form of an instruction in a CPU.

megahertz (MHz)

One million cycles per second. The internal clock speed of a microprocessor is expressed in MHz.

gigahertz (GHz)

One billion cycles per second. The internal clock speed of a microprocessor is expressed in GHz.

bit

A binary digit. The digit is the smallest unit of information and represents either an off state (zero) or an on state (one).

Another noticeable difference among processors is the type of instruction set they use. The instruction sets that are most common to processors are either Complex Instruction Set Computing (CISC) or Reduced Instruction Set Computing (RISC).

CISC has been a common method of processing operations, especially in Intel CPUs. CISC uses a set of commands, which include subcommands that require additional CPU memory and time to process. Each command must go through a decode unit, located inside the CPU, to be broken down into microcode. The microcode is then processed one microcode at a time, which slows computing.

RISC, on the other hand, uses smaller commands that enable it to operate at higher speeds. The smaller commands work directly with microcode, so there is no need for a decode unit. This factor-along with a RISC chip's capability to execute multiple commands simultaneously-dramatically increases the processing power.

Finally, different manufacturers design processors to varying specifications. You should be sure that the processor type and model you choose are compatible with the operating system that you want to use. If the processor is not 100 percent compatible with the operating system, the computer will not operate at its best or might not work at all.

Note 

The terms processor, microprocessor, chip, and CPU are used interchangeably.

Deciphering Processor Terminology

For most computer novices, terms such as microcode efficiency and internal cache RAM can sound like part of a foreign language. To help you keep things straight, here are some common terms and their definitions:

Clock cycles  The internal speed of a computer or processor expressed in megahertz (MHz) or gigahertz (GHz). The faster the clock speed, the faster the computer performs a specific operation.

CPU speed  The number of operations that are processed in one second.

Data path  The number of bits that can be transported into the processor chip during one operation.

Floating Point Unit (FPU), or math coprocessor  A secondary processor that speeds operations by taking over math calculations of decimal numbers. Also called a numeric processor.

Level 1 (L1), or internal, cache  Memory in the CPU that is used to temporarily store instructions and data while they are waiting to be processed. One of the distinguishing features of different processors is the amount of internal cache that is supported.

Level 2 (L2), or backside, cache  Memory that is used by the CPU to temporarily store data that is waiting to be processed. Originally located on the motherboard, CPU architectures such as the Pentium II, III, and 4 have incorporated L2 cache directly on the same board as the CPU. The CPU can access the on-board L2 cache two to four times faster than it can access the L2 cache on the motherboard.

Microcode efficiency  The capability of a CPU to process microcode in a manner that uses the least amount of time and completes the greatest number of operations.

Word size  The largest number in bits that can be processed during one operation.

Note 

All the computer's components, including the processor, are installed on the motherboard. This fiberglass sheet is designed for a specific type of CPU. When purchasing a motherboard, you should check with the motherboard manufacturer to determine which types of CPUs are supported.