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The pins that attach the chip to the motherboard come in two forms: the Dual In-Line Package (DIP) and the Pin GridArray (PGA). DIP pins are identified as two rows, located on opposing sides of the chip. PCs using either the 8088 or 8086 processor used 40-pin DIPS. The PGA chip has pins arranged in rows on each of the four sides, and was used in PCs using the 80286, 80386, 486 and the first Pentium CPUs (60 MHz and 66 MHz). Later Pentiums (75 MHz and up) used a slightly different form factor called the Staggered PGA, and the Pentium lI dispensed with sockets entirely by going to a cartridge type mounting method called "slot-1."
Just as you need a work surface,whether it is a desk in an office or a countertop in your kitchen, your computer also needs a work area. This area, called memory, is used by the computer to store the instructions from your applications and manipulate data. Memory is comprised of integrated circuits (ICs) that reside on a chip. ICs work in a manner similar to a light switch in that each circuit can have only one of two states: on or off. Your computer recognizes an off switch as a numerical 0, whereas an on switch is translated as a numerical 1. This binary pattern of Os and 1 s is how your computer stores, retrieves, and communicates data. Memory is broken up into several types: Random Access Memory (RAM), Read-Only Memory (ROM), and cache memory.
RAM is the most common type of memory chips used for the CPU's main memory: the CPU loads your programs into RAM, runs the program's instructions from RAM, loads data into RAM, and manipulates the data while it is in RAM. RAM is sometimes called by its more specific name, DRAM (Dynamic RAM), which is the basis for all main memory chips in all PC systems.
ROM is a memory chip that is also part of main memory, except that its contents are written only once, usually at the factory, and when used in a PC system can only be read, hence the name Read-Only. ROM usually stores only the Basic Input Output System (BIOS), which is the set of instructions that your computer uses to boot.
Cache memory is made up of much faster memory called SRAM (Static RAM). Starting with the 80386 CPU, DRAM could not work as fast as the CPU and therefore created a bottleneck that slowed down the CPU. SRAM, which runs up to ten times as fast, could not practically replace DRAM since it also costs ten times as much. However, it was discovered that a small, relatively inexpensive cache of SRAM memory chips could keep copies of the most frequently used main memory locations, and enable the main memory to keep up with the CPU 90% of the time. The faster the CPU, the more cache is needed to maintain that 90% edge. Early 386 systems typically used 64KB or 128KB of cache memory on the motherboard. 486 and Pentium CPUs have added a primary SRAM cache on the CPU chip itself, using a secondary memory cache on the motherboard of 128KB to 1MB in size. The Pentium-Il CPU includes a 512KB or 1MB cache built into the processor cartridge (in addition to an on-chip primary cache of 32KB) and therefore needs no memory cache on a the motherboard. All of these design combinations result in an overall memory system performance of 85% to 95% of the theoretical maximum performance, for thousands of dollars less.
Information has become one of the most important commodities to individuals and businesses today. In the past, data was kept in the form of paper documents held in rows of file cabinets. Storing that information for any length of time became an almost impossible task due to space limitations. When personal computers began populating offices, their storage potential began to be explored. The first computers used floppy disks and hard drives, but today's computers have a wider variety of storage media available, such as CD-ROMs, tape drives, optical drives, Zip drives, and jaz drives. Do not expect any questions on your exam on jaz and Zip drives, as these are not standard hardware devices found on all computers. However, many leading computer manufacturers are including jaz and Zip drives with their computers.
Shortly after the first computers were invented, it was discovered that magnetic tape could store information as a series of is and Os. However, magnetic tape can only store data sequentially, and is most commonly used as a backup medium. As tape drives are not covered on the A+ Certification exam, they get only a brief mention here.
Floppy drives write data on disks that are inserted and removed from the drive. The actual disk is encased in an envelope, which has a small opening to allow a read/write head to access the disk. The read/write head passes over the disk, reading data from or writing data to the disk itself. Floppy drives, and the disks used by them, come in two sizes: 5.25° or 3.5".
The 5.25" drives are the older of the two, and are seldom used today. The original single-sided drives had a capacity of only 180 kilobytes. Double-sided drives and disks were later introduced, which increased the storage to 360KB. The 5.25" disks eventually reached a capacity of 1.2MB as technology refined both the accuracy of the drives and the surface of the disk...