Sunday, September 6, 2009

The first x86 design(8086)

The 8086 was originally intended as a temporary substitute for the ambitious iAPX 432 project in an attempt to draw attention from the less-delayed 16 and 32-bit processors of other manufacturers (such as Motorola, Zilog, and National Semiconductor) and at the same time to top the successful Z80 (designed by former Intel employees). Both the architecture and the physical chip were therefore developed quickly (in a little more than two years[6]), using the same basic microarchitecture elements and physical implementation techniques as employed by the older 8085, and for which it also functioned as its continuation. Marketed as source compatible, it was designed so that assembly language for the 8085, 8080, or 8008 could be automatically converted into equivalent (sub-optimal) 8086 source code, with little or no hand-editing. This was possible because the programming model and instruction set was (loosely) based on the 8080. However, the 8086 design was expanded to support full 16-bit processing, instead of the fairly basic 16-bit capabilities of the 8080/8085. New kinds of instructions were added as well; self-repeating operations and instructions to better support nested ALGOL-family languages such as Pascal, among others.
The 8086 was sequenced[7] using a mix of random logic and microcode and was implemented using depletion load nMOS circuitry with approximately 20,000 active transistors (29,000 counting all ROM and PLA sites). It was soon moved to a new refined nMOS manufacturing process called HMOS (for High performance MOS) that Intel originally developed for manufacturing of fast static RAM products[8]. This was followed by HMOS-II, HMOS-III versions, and, eventually, a fully static version designed in CMOS and manufactured in CHMOS.[9] The original chip measured 33 mm² and minimum feature size was 3.2 μm.
The architecture was defined by Stephen P. Morse and Bruce Ravenel. Jim McKevitt and John Bayliss were the lead engineers of the development team and William Pohlman the manager. While less known than the 8088 chip, the legacy of the 8086 is enduring; references to it can still be found on most modern computers in the form of the Vendor ID entry for all Intel devices, which is 8086H (hexadecimal). It also lent its last two digits to Intel's later extended versions of the design, such as the 286 and the 386, all of which eventually became known as the x86 family.

No comments:

Post a Comment