The System Unit

The motherboard in the system unit contains different types of chips. Manufacturers package chips so the chips can be attached to circuit boards, such as the motherboard.

Types of chip packages include:

Dual inline package (DIP), which consists of two parallel rows of downward-pointing thin metal feet (pins)

Pin grid array (PGA) package, which holds a larger number of pins because the pins are mounted on the surface of the package

Flip chip-PGA (FC-PGA) package, which places chips on the opposite side (flip side) of the pins

Single edge contact (SEC) cartridge, which connects to the motherboard on one of its edges

The CPU

The power of personal computer processor chips (the chips that contain the CPU) has grown at an astounding rate. As chips become older and more widely used, price cuts usually are introduced.

Several factors affect CPU processing speed. CPUs in most of today’s personal computers use pipelining, a technique that increases processing speed by beginning execution of a second machine cycle instruction before the first instruction is completed. CPUs also use high-speed storage locations, called registers, to hold data and instructions temporarily. The control unit relies on a small chip called the system clock to synchronize all computer operations. The speed at which a processor executes instructions is called clock speed, or clock rate, and is measured in megahertz (MHz). The system clock is a major factor affecting processor speed. A higher clock speed means the CPU can process more instructions per second.

Processor Comparison

Although once frequently used, the term “microprocessor” is much less common today.

Sometimes you can upgrade your processor to increase the computer’s performance. There are three forms of upgrades:

·         With a chip for chip upgrade, the existing processor chip is replaced with a new one

·         With a piggyback upgrade, the new processor is stacked on top of the old one

·         With a daughterboard upgrade, the new processor is on a small circuit board (the daughterboard) that plugs into the motherboard

The past three years have seen a steady drop in the cost of computers. PC prices plunged as a result of lower prices for processors, memory chips, and hard drives. Consumers also are showing increased interest in new less powerful, but less expensive, personal computers that work perfectly well for the most popular uses – word processing, Internet access, and spreadsheet applications. The surge in low-priced computer sales has had an impact on Intel, the world’s largest processor manufacturer. By focusing on making inexpensive processor chips, rivals AMD and Cyrix are making inroads into Intel’s dominance. Intel’s response, the Celeron™, has proven popular, but the lower-priced chip offers a smaller profit margin.

Data Representation

Just as the decimal system (10 digits) is suited to human anatomy (10 fingers), the binary system (2 digits) is perfect to represent the on-off states (2 states) of a computer. Basic coding standards make it possible for components within computers to communicate, allow manufacturers to be confident that the components they produce will operate correctly in a computer, and enable consumers to purchase components that are compatible with their systems. In the ASCII-8 and EBCDIC codes, the first four characters represent the zone, and the last four characters represent the digits 1 through 8. ASCII, originally a seven-bit code, was expanded to eight bits in an effort to provide for symbols used in other nations. Unicode, a 2-byte (16-bit) code, can represent 216, or 65,536, characters. The system employs the codes used by ASCII and also includes other alphabets (such as Cyrillic and Hebrew), special characters (including religious symbols), and some of the “word writing” symbols used by various Asian countries.

Memory

Because computers use the binary number system, the actual values for the units in which memory and storage are measured are based on powers of 2. For example, one kilobyte = 210 = 1,024.

RAM’s volatility, and its ability to be changed, are its most distinguishing characteristics. When RAM is purchased it comes in banks of nine chips – eight are needed to represent a byte and the ninth is needed for parity. RAM chips usually are packaged on small circuit boards called single inline memory modules (SIMMs) or dual inline memory modules (DIMMs) that are inserted into the motherboard. During the past 20 years, the price of RAM has dropped an average of 20 percent each year, but its capacity has more than doubled every two years.

Similar to flash ROM, another variation of ROM, called EEPROM (electrically erasable programmable read-only memory), can be erased electrically and rewritten. Because of its non-volatile nature, EEPROM is used in electronic cash registers to store item prices.

The amount of time it takes the processor to read data from memory, called access time, directly affects how fast the computer can process data. Memory access time is measured in terms of nanoseconds, or billionths of a second.