4. Memory Protection

The one feature Intel offered that made it the microprocessor of choice was memory protection. When we had a simple operating system and ran one program at a time, memory protection wasn't an issue. Now that we are running multi-threaded OSs and have a dozen applications in memory simultaneously, there was a need for a more sophisticated memory addressing method than the simple flat model.

In the flat model, when a program runs away it can mess up the code or data from other programs. This was difficult to debug because there was no indication of which application caused the problem. With the Intel segmented architecture, a program cannot delve into the memory space allotted to another application. If it tries, a memory fault message is generated and only that program crashes. You usually can recover from this situation without having to reboot and you know exactly which program was the culprit.

5. Multitasking

The Intel 386 was a break-through microprocessor in another very important way. It had hardware and special instructions that supported true multitasking. Nowadays, we take it for granted that several applications can run simultaneously. In actuality, only one program is executed at any particular time. Your computer runs so fast that it can let each program run for just a short bit of time, then switch to the next program.

Prior to the 386, in order for two pieces of software to be in memory and multitasking back and forth, the software had to be specially written to run for that short time. This scheme depended on the software to cooperate, a burden that rarely worked out in the real world.

The 386 could stop a program in its tracks and suspend it while other programs ran. Then the OS would switch back to the first program as if nothing had ever stopped it. This is called preemptive multitasking and is an important concept to remember for later. Finally there was a window of opportunity for the Microsoft Windows operating system!

6. Multi Data

The microprocessor was just now catching up to the features of the mainframe and minicomputers that came before it. In 1997, Intel introduced their MMX feature with the Pentium II microprocessor This is a trade name for Single Instruction, Multiple Data (SIMD) capability.

Playing video games on a personal computer was all the rage and even engineers wanted faster graphics performance for rendering 3D models. The Pentium class microprocessors could handle data in 64-bit chunks, which was great for heavy-duty scientific calculations, but graphics number crunching only needs 8-bit numbers and it needs it fast!

A peculiarity of video processing is that the microprocessor has to do the same calculation over and over for all the pixels on the screen. The Intel engineers devised a way to reuse the 64-bit calculation hardware by splitting it up into smaller pieces; either two 32-bit, four 16-bit or eight 8-bit registers. The calculations were restricted to integers making it ideal for the simple graphics processing of the day.