Happy anniversary, 80286
The month of February 2014 marks the 32nd anniversary of the debut of the Intel 80286 CPU, a historical processor of changing fortunes which helped to build what would have later become the market domination of the x86 instruction set. As Computer Hope reminds, the 286 processor (also known as “iAPX 286”) was introduced on February 1st in 1982 bringing important technology innovations a bit too ahead of the times.
In addition to being the heart of the 16 Mhz system where who writes humbly started to furiously click on a computer keyboard many years ago, the 80286 was employed by IBM in the second generation of its original “Personal Computer” better known as PC/AT (1984). The 286 was the second iteration of the 16-bit x86 technology introduced by Intel with the 8086 CPU (used on the IBM 5150), it was widely used for the “IBM compatible” PCs sold during the Eighties and the Nineties and it was the first x86 processor to embed memory management and code protection features.
80286, internal view
Provided with 134,000 transistors, a 24-bit address bus and a 6 MHz base clock (compared to the 25 MHz of the most powerful models made by Harris Corporation), the 286 could support a total of 16 Megabytes of RAM compared to the single Megabyte of the 8086 – although at that time the software designed to benefit from a larger amount of memory was rare and the cost of the additional memory chips rather expensive. With the 286 Intel introduced for the first time the protected mode, a new code execution mode adding up to the real mode of the previous x86 CPU generation where the software could have used the aforementioned 16 Megabytes thanks to the availability of the memory management unit (MMU) embedded in the processor.
The MMU provided protection against unauthorized writings by malfunctioning software outside the allocated memory zones, and in theory it should have helped to promote real multitasking for running multiple programs at once. In practice, the new protected mode wasn’t compatible with the x86 software already on the market and it didn’t provide a way to return to the 8086 real mode without a hardware reset, hence PC users started to really enjoy the benefits of having amounts of memory larger than the infamous limit of the MS-DOS conventional memory (the first 640 Kilobytes of system memory) only with the 80386 and later CPUs. The rest, as they say, is history.