2.3 Hardware Components
2.3.3 The CPU
The CPU is one of the most important elements of the personal computer. On the motherboard, the CPU is contained on a single integrated circuit called the microprocessor. The computer will not run without a CPU. Often referred to as the brains of a computer, the CPU contains two basic components:
  • A control unit instructs the rest of the computer system on how to follow a program instructions. It directs the movement of data to and from processor memory. The control unit temporarily holds data, instructions, and processed information in its arithmetic/logic unit. In addition, it directs control signals between the CPU and external devices such as hard disks, main memory, I/O ports, and so on.
  • An Arithmetic/Logic Unit (ALU) performs both arithmetic and logical operations. Arithmetic operations are fundamental math operations like addition, subtraction, multiplication, and division. Logical operations such as the AND, OR, and XOR are used to make comparisons and decisions, and these determine how a program is executed.

The processor handles most of the operations that are required of the computer by processing instructions and sending signals out, checking for connectivity, and ensuring that operations and hardware are functioning properly. It acts as a messenger to major components such as RAM, the monitor, and disk drives. The microprocessor is connected to the rest of the computer system through three buses, including the data bus, address bus, and control bus (the bus types are discussed in detail later in this chapter).

There are many different companies that produce CPUs, including Intel, Advanced Micro-Devices (AMD), and Cyrix. Intel is credited with making the first modern, silicon-based CPU chip in 1971.

Processor Socket Types and Slots
In dealing with microprocessors, such terminology as Socket 7, Socket 370, Socket 423, or Slot 1, will frequently be encountered. Socket X (X being any numerical number) is a descriptive term for the way certain processors plug into a computer motherboard so that it makes contact with the built-in circuitry or data bus of the motherboard. Manufacturers can have different socket types for their processors. Socket 7, mostly outdated, is the best known of the major connection variations that have been designed. It is used by some generation of each of the three major processor types: AMD, Intel, and Cyrix. Socket types that are followed by a larger number (in the naming) are more current. For example, Socket 370 and up are more current than anything lower. The progression from Socket 1 (Intel 486 processors) through Socket 423 (Intel Pentium 4 processors) has come along with improved processor technology and speed. Table summarizes information on socket types and the different processor types that use them.

Socket 7 and other socket-type processors use the Zero Insertion Force (ZIF) socket. A ZIF socket is designed to make it easy to replace and upgrade the microprocessor. A typical ZIF socket contains a lever that opens and closes, securing the microprocessor in place. Additionally, the various sockets have a differing number of pins and pin layout arrangements. Socket 7, for example, has 321 pins, but the number of pins generally increases with the socket numbering. Slot-type processors had a very brief lifespan (just about a year in the market). Intel, for its Pentium II processor, moved from the socket configuration to a processor packaged in a cartridge that fits into a slot in the motherboard. Similarly, AMD has progressed to Slot A (similar to Slot 1) and then to Socket A for its high-end AMD Athlon™ and Duron processors.

Pentium Processors
The current family of the Intel Pentium microprocessors includes the Pentium II, III, IV, and Xeon. The Pentium class is the current standard for processor chips. These processors represent the Intel processor second and third generations. By combining memory cache with microprocessor circuitry, the Pentium supports processor speeds of 1,000MHz and more. The combined chips cover less than 2 square inches (6 cm2) and comprise over a million transistors.

The Pentium processors have made several improvements over their predecessor, which evolved from the Intel 80486. For instance, the Pentium data bus is 64 bits wide and can take in data 64 bits at a time, compared to 32 bits with the Intel 486. The Pentium has multiple caches of storage totaling as much as 2 MB compared to the 8 kilobytes of the Intel 486.

Software can run twice as fast on the Pentium because the components are designed to get data in and out of the chip quickly to ensure that the parts performing the actual data manipulation will never go idle waiting for data or instructions. These components need to handle the flow of information through the processor, interpret instructions so the processor can execute them, and send the results back to the PC's memory. The manufacturer's website, www.intel.com provides more about the Pentium family of processors (P1, PII, PIII, PIV, and Xeon).

AMD Processors
The best performing Advanced Micro Devices (AMD) processors are the Athlon, Thunderbird, and Duron series. They are currently the most used microprocessors, along side the Intel Pentium IIIs, in high-end desktop systems, workstations, and servers. The AMD Athlon processor system bus is designed for scalable multiprocessing, with the number of AMD Athlon processors in a multiprocessor system determined by chipset implementation. The manufacturer's website, www.amd.com, provides more about the AMD family of processors (Athlons, Thunderbird, and Durons).

Processor Speed Rating
CPU descriptions as Pentium 133, Pentium 166, or Pentium 200 are well known. These numbers are specifications that indicate the maximum (reliable) operating speed at which the CPU can execute instructions. The CPU speed is not controlled by the microprocessor itself, but by an external clock located on the motherboard. The speed of the processor is determined by the frequency of the clock signal. It is typically expressed in megahertz (MHz), and the higher the number, the faster the processor. Currently, there are processors with speeds of up to 1.5 GigaHertz (1,500 MHz).

The CPU speed and the frequency of the clock signal are not always at a one-to-one ratio. This is because CPUs can run at a much higher MHz internally than the other chips on the motherboard clock can operate. A variable-frequency synthesizer circuit built into the motherboard circuit multiplies the clock signal so that the motherboard can support several speeds of CPUs. Generally, three factors determine how much information can be processed at any given time. These include:

  • The size of the internal bus
  • The size of the address bus
  • The processor's speed ratings
     
Lab Activity  (PDF, 9 KB)
  In this lab, students will be able to locate and identify the type of CPU and CPU Socket on the motherboard.