A History of Overclocking Part One

386
(1986-1989, 1.5µm - 1µm process, 16-40MHz)

The next evolutionary step was introduced with the 386. It could be argued that this 32-bit chip popularised PCs, but it wouldn’t be until 1995 that we’d get an operating system that could take advantage of its registers. By the time Windows 95 came out, the OS was capable of crippling a fast 486, let alone a 386. The clone PC market started with gusto, with Compaq beating IBM to market.

The hundreds of components featured on the 8088 and 80286 motherboards had been condensed into one chip, called the ‘chipset’ by a company named Chips and Components. The idea caught on rapidly and there were many competitors, but by 1994 there would only be one powerhouse chipset manufacturer – Intel.

There were two types of desktop 386 – the SX, which had a 16-bit external bus and was soldered to the motherboard, and the DX, which got the full 32-bit both inside and out and was socketed.



Overclocking the 386 had shifted from the days of clock crystal swapping. While these days we tend to use jumpers purely to reset the CMOS, banks of the things or a series of DIP (Dual Inline Package) switches were on motherboards that would do things such as manually set IRQs, voltages, allow the BIOS to be written to and to set the speed of the FSB. Before the 286 days these would even determine what hardware was present in the machine, but by this time that functionality had been shifted to the BIOS, and hardware was automatically detected instead.

The 386 brought 32-bit Protected Mode into play – allowing the system to address 4GB of memory – and could auto-switch between Real and Protected with no problems. A third mode, Virtual Mode – otherwise known as VM86 – was introduced, making it feasible to run a number of virtual machines simultaneously within a Protected environment. This lead to multitasked DOS programs through managers such as QuarterDeck’s DesQView.

Cache was provided for the first time asynchronously on the motherboard, as DRAM could no longer keep up with speeds beyond 16MHz, 64KB of cache of the huge, socketed SRAM being the highest you could get.

Intel refused to reveal the specs of the 386 to AMD, which ended in Intel attempting to nix the agreement for AMD’s access to all x86 code. Several court cases later, it was determined that AMD had the right to copy Intel’s x86 architecture through the companies’ 1982 agreement. As such the AM386 was the first AMD in-house designed chip, although large portions were reverse engineered from Intel’s solution.

To this day, Intel is still making its 80386 as an embedded processor, with production slated to stop in 2007 – a good 21 years after its introduction.


486
(1989-1993, 0.8µm Process, 25-100MHz)

The 486 arrived and while the SX variants like the 386 were floating point crippled and soldered, the DX units came with the FPU integrated, removing any off-die bottlenecks.

Heatsinks on later 486 chips introduced a low-profile fan mounted to a thin piece of copper sitting on top of the CPU, bonded by thermal glue or held down by plastic clamps – the fan, sink and CPU all the same dimensions. For the most part though a passive heatsink was used.

VESA Local Bus, or VLBus was introduced at this stage to overcome video card bandwidth issues related to the ISA slot. This existed as an ISA port with a separate extended port below it, and although it was asynchronous it was often set to run at the same speed as the FSB, from 25 to 50MHz.

Memory by now was up to 60ns, and the 486 introduced burst mode – after a read the machine could then access the next three adjacent states with no latency penalty or wait states. The amount of cycles need to access the four states were referred to in the form of x-y-y-y, where ‘x’ equalled the first access time (latency + cycle time) and ‘y’ represented the cycles required for each following access. Today these are known as CAS Latency (CL), RAS to CAS Delay (tRCD), RAS Precharge (tRP) and Active to Precharge delay (tRAS).

At this time, standard RAM was rated at about 5-3-3-3. This came in a 30-pin Single Inline Memory Module (SIMM) form factor, and began creeping in with late 386 boards. SIMMs ran on an asynchronous 16MHz bus, making it a bottleneck compared to the processor.