Math Coprocessor
The Generations of early vintage PC computers can be divided based on the family type of CPU processor used in the computer.
Here are the basic family lineages of these CPUs
1) The Original the Granddaddy – “8088″
The 8088 is slow slow slow. At the time (1981) it seemed like a very hot item.
The Intel 8088 is an Intel microprocessor based on the 8086, with 16-bit registers and an 8-bit external data bus.
The most influential microcomputer to use the 8088 was, by far, the IBM PC. The original PC processor ran at a clock frequency of 4.77 MHz. A popular clone using an 8088 was the Leading Edge Model D, with a switch to select running at 4.77 MHz or 7.16 MHz.
2) 802286
The 286 was the next generation of vintage computers in the mid 1980’s era. A 286 family computer is about three to four times faster than an 8088 based PC.
The biggest problem with a 286 chip is that it does not handle memory well as a 386 (next step in the line) computer. It has a different instruction set (the programming telling a chip what to do), which is just slightly incompatible with the 386.
These differences, plus the slow speed, that made the 286 almost incompatible with the newer software sealed the 286’s doom.
3) 80386SX and DX
In its day the 386 chip was a revolutionary change in computing which paved the way for later major upgrades in computing.
We owe much in our days of Pentium 4s to the early days of the 386 computers.
Compared to a 286, the 386 had a huge amount of addressable memory. The 386 came in two basic flavors – SX and DX – and in a whole range of speeds. The 386 SX was a bridge between the 16-bit and the 32 bit chips.
Higher clock speeds certainly boosted performance, but the most noticeable change was the move from 16 bit to 32 bit computing. When that occurred, performance was doubled immediately, since twice as much data could be moved and used. It is like grabbing twice as big a handful. The bigger the handful grabbed the more that can be moved at a time. Today this seems commonplace however at the time it was more than a major step leading to our current 32 bit and now 64 bit computers ( one more step we should be grateful for the 386 for leading us to ).
80486
The 486 was a more affiancing design than the lowly 386. It incorporated a built in 8 kb cache and cache controller (kb as opposed to megabyte which is 1000 kb). As well a Math Coprocessor, better architecture and memory management for 32 bit operations were part of the package. The cache gave a boost to overall performance while still using the relatively inexpensive dynamic random access memory (DRAM), DRAM was a volatile type of main memory,
Cache serves a simple way to speed up the 486 computer. The cache anticipated the next instructions based on what was being done and stored it in a hiding place in memory. Then when the instructions or data was needed it was retrieved fairly rapidly from the hiding place in memory.
A 486 could process 32-bit instructions much faster than any 386. However DOS based software as it was written primarily for 8 and 16-bit systems could not take advantage of these advances.
OS/2 a multitasking operating system developed by Microsoft and Windows 3.0 and later 3.1 are able to take full advantage of the 486’s features.
80486DX2
The 486DX2 was a peculiar chip that ran internally twice as fast the external system. In other words, if a machine was designed to run a 25 MHZ 486, you could put in the 50 MHZ 486DX2 and it would work fine without any major changes to the rest of the computer. It would not run as fast as a 50 MHZ 486DX though. Only the innards of the CPU are running as fast on a DX2 chip – the rest of the computer is running at the speed designated around the 25 MHZ chip. This is a little confusing, but suffice to say that a 50 MHZ 486DX had more performance than a 50 MHZ 486DX2. Perhaps this however was little more than an Intel marketing gimmick.
804486SX
The 486SX was a slowed down 486.
It ran at 16, 20 and 25 MHZ.
Basically in a 486SX the math coprocessor chip was disabled.
The 486SX was a budget entry level chip meant to upgrade users from their 386 at less cost. Or it may have been seen as the 2 door car to get you into the car showroom or steer you away from competitors.
Lastly the 80486DX3
These were IBM licensed chips that were clock tripled 486 chips running at 75 MHZ and 99 MHZ (called conveniently 100 MHZ speed)
The Intel versions were called the DX4
It needs not be said that these chips were far than overshadowed by later Pentium processors of the same or greater speeds.
Generally the speed of the computer CPU goes more than family than speed. That is a 75 MHZ (later model) Pentium will almost certainly beat out a 100 MHZ 486 CPU.
About the Author:
Mr. Arthur Felon Dept Head IT Ace Employment Services http://www.aceemploymentservices.net artfellon@yahoo.com Specific interest in Vintage Computing Technology Blog : http://www.vintageomputermanuals.com http://www.vintagecomputermanuals.com
Article Source: ArticlesBase.com – Computing – The Basic Generations Of The Early Pcs An Their Legacy
