Phil Storrs PC Hardware book

Time-line of an Entry Level PC

Over the last few years we have been able to define an "entry level" PC computer by its processor. The PC stated out with the 8088 chip in the original IBM PC of 1981 and progressed to the 80286 based AT in 1983. The XT type (8088 based) eight bit bus computer had a long and productive life.

The Clone machines underwent many improvements along the way, the clock speed increased to 8, 10 and then 12MHz, and some of the last generation of XT type clone machines used an 80286 processor running at 16MHz, instead of an 8088 chip. NEC produced a better clone of the 8088 chip, the V20, and this was used in many of the last generation of XT type computers. Some manufacturers used an 8086 chip or the NEC V30, and accessed the RAM 16 bits at a time, instead of 8 bits at a time.

The XT type computer with its eight bit external data bus, and 20 bit address bus, was the most common PC until 1987 when 80286 based computers (PC/AT), with their 16 bit external data bus and 24 bit address bus, started to become affordable.

By 1987 the entry level machine had progressed to an 80286 based computer. IBM used the name PC/AT for these computers, clone manufacturers usually called them 286 computers. 1987 saw the introduction of the 80386 chip and by 1991 the entry level machine had progressed to an 80386SX based machine. The rest of the progression to the present day and beyond roughly follows the following list.

Year Processor
1992 386DX40
1993 486SX25 or 33
1994 486DX33
1995 (first half) 486DX2/66
1995 (second half) 486DX4/100
1996 (first half) Pentium 75
1996 (second half) Pentium 100
1997 (first half) Pentium 133, Cyrix/IBM or AMD equivalent
1997 (second half) Pentium 166 to 200, Cyrix/IBM or AMD equivalent
1998 (first half) Pentium MMX 200, Cyrix/IBM or AMD equivalent
1998 (second half) Celeron or Celeron A 300MHz, AMD K6-2/300, or 6x86/300

A bit more History

In 1987 in a bid to regain the dominant position they had in the early days of PC's, IBM changed direction with a new naming convention, a new advanced Bus slot and a new Operating System. The PS/2 range from IBM introduced the MCA (Micro Channel Architecture) Bus and OS/2. The first PS/2 was the Model 30, a slightly updated 80286 based computer running a higher clock speed than the IBM PC/AT and still using the ISA Bus. The other leading manufacturers of PC computers (Computers using Intel family Processors) continued on with DOS, and the ISA Bus and soon developed an advanced version of the ISA Bus called EISA. Gradually DOS gave way to Windows and IBM never regained a significant market share of the PC market. The PowerPC was a further attempt by IBM at taking over the market during the mid 1990's but this failed.

Clock Speeds

All the various 8086 family processors have been available in a range of clock speeds and the faster chips have always cost more than their slower relations. The 80386DX chip started out running at 16 MHz and was eventually available in a 40 MHz version from AMD. The 386SX chip started out at 16 MHz and eventually was available with a clock speed of 33 MHz. The 386 and 486 generation Processors accessed the RAM at the Clock Speed of the processor.

The 486SX chip was first available for a 25MHz clock speed and then for 33MHz and eventually a 486SX2/66 was produced. The 486DX chip was first produced operating at 33MHz but a 50MHz version was also available from Intel and a 40MHz version from AMD.

The next step was to double the Clock Speed inside the Processor. The 486DX2/66 Processor operates with an External Clock Speed of 33 MHz and an Internal Clock Speed of 66 MHz. The DX4/100 processors operate with an External Clock Speed of 33MHz and an Internal Clock Speed of 100 MHz. AMD produced 486DX2/80 and 486DX4/120 chips that operated with an External Clock Speed of 40MHz.

The INTEL 486 OverDrive Processors

Intel produced a range of OverDrive processors that were upgrade devices. The first OverDrive processor was the 486 OverDrive and this was an enhanced 486DX2/66 chip with a built in voltage regulator and heat sink. This was followed by a 486DX4/100 OverDrive chip.

OverDrive processors are mainly used by Corporate and Government users who often have budgets to upgrade or repair existing Equipment, rather than replace equipment. IBM and Cyrix also looked at this market for a while but it appears as though there is only a small market for this type of product.

Two other products, the Evergreen and Power Leap chips are re-packaged and re-badged 80586 chips mounted on a sub-board that plugs into a 80486 System Board. The board is required to provide the 3.3 volt supply to the processor because many older 80486 System Boards only have a 5 volt supply to the processor chip.

Intel Pentium OverDrive

Intel is producing a Pentium OverDrive chip for use in old Pentium boards that were designed for the 60 and 66 MHz Pentium chips only (these Pentiums used an older socket) and another for System Boards that can only handle 75 and 100 MHz Pentiums. These chips are expensive and only give a maximum performance boost of 50%. The other technology involved in a PC Computer, particularly RAM technology, is advancing at such a rate it is far more cost effective to replace all the hardware, System Board, RAM and Video card.

NexGen (now part of AMD) produced a processor called the Nx586, a 486 compatible device similar to the Pentium OverDrive from Intel. Another similar device was also marketed by IBM/Cyrix as the 5x86 chip. All of these chips had a 32-bit External Data bus and a 64-bit Internal Data bus.

Back to the The Pentium and beyond chapter Back to the opening index Book one index

Whats inside the first generation Pentium Processor Time line of Intel processors Internal and external speeds of older Pentium type processors The Sub US$1000 PC

Copyright © Phil. Storr, last updated 26th December 1998