The Electronic Labyrinth

IBM Compatible Computers

Personal computers based on CPUs (Central Processing Unit) manufactured by Intel have evolved through several generations since their inception. These have seen increases in transistor density, clock speed, bit path, and instruction sets. All models run the Disk Operating System (DOS) designed by Microsoft Corp.

The clock speed of the chip, measured in megahertz (MHz), indicates the speed at which a single instruction may be executed. The width of the bit path indicates how much data can be transferred at one time within the chip. As either of these numbers increases, the overall performance improves. This is measured in Millions of Instructions Per Second (MIPS).

The first IBM PCs (later called XTs) were introduced in 1981. They used either 8088 or 8086 CPUs, both of which are 8-bit chips running at 5 MHz (0.33 MIPS). They came with monochrome monitors and dual 5.25" floppy drives, later including small (10-20 MB) hard drives. The 8088 and 8086 are restricted to using 640 KB RAM (Random Access Memory), into which the operating system, drivers for devices such as a mouse or CD-ROM, software code, and data must all fit.

A breakthrough came with the introduction of the 80286, a 16-bit chip that could operate in "protected mode," thus permitting software to "break the 640 KB barrier." In effect, this meant that memory above 1 MB could be used as extended or expanded memory. (These terms are not synonyms, but the distinctions are unimportant here.) Memory between 640 KB and 1 MB is used internally for graphics, low-level functions, and so on.

This chip was first used in the AT, the second generation of IBM computers, released in 1984. Initial models ran at 8 MHz (1.2 MIPS), and were available with colour monitors (CGA, EGA) and larger hard drives (typically 40 MB). Still later, monitor resolutions improved to VGA, and 3.5" floppy drives became standard.

Unfortunately, DOS could not utilize protected mode. Neither were many software packages able to use memory beyond 640 KB. It was not until the development of the 80386 that software caught up with hardware to the point that there was no longer any practical limit on memory usage.

The first computer utilizing the 80386 was introduced in 1986 by Compaq. This machine ran at 16 MHz for a full 6 MIPS of power. Later models were capable of twice this rate. More important than sheer speed, the '386 implemented "virtual mode," which allowed multiple 8086 sessions. Software environments such as DesqView and Microsoft Windows used this ability to implement multi-tasking on a desktop computer.

More recently, an entire encyclopedia of chips has been made available by AMD, Cyrix, and other companies that have cloned Intel's design. In a rush to outdistance this new competition, Intel has produced more powerful processors such as the 80486 (which features a built-in math coprocessor) and such oddities as the 80386 SX and 80486 SX, crippled versions of their parent chips. These exist not for technological, but rather for marketing reasons.

The newest processor is not named the 80586 (numbers have proven to be unprotectable under trademark law), but rather the Pentium. Feibus and Slater have discussed this newcomer in detail. Suffice it to say that this 64-bit chip runs at 66 MHz, contains 3.1 million transistors, and clocks in at 112 MIPS, 340 times faster than the lowly 8086.

Though incredibly fast chips are becoming an affordable luxury, they do not necessarily increase the user's efficiency. Most of the time, the processor is idling, waiting for instructions. It is commonly believed that the next true breakthrough in productivity will occur at the operating system level. DOS was designed when 256 KB was a lot of memory, and 10 MB a large disk. Though it continues to be improved, the underlying architecture is not robust enough to deal with the demands of today's applications.

According to International Data Corp, as of December 1992, 22% of users had an 8088/8086, 37% used an 80286, and 46% used an 80386 or better (PC Week, January 18th, 1993). These statistics are important to hyperbook authors, as they dictate the readership available when choosing a given hardware platform.

© 1993-2000 Christopher Keep, Tim McLaughlin, Robin Parmar.
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