Comment by mbf1
8 hours ago
There were a couple interesting points about the market for 8087 chips -- Intel designed the motherboard for the IBM PC, and they included an 8086 slot and a slot for either an 8087 or 8089. IBM didn't populate the slot for the coprocessor chip as it would compete with their mainframes, but Intel went around marketing the chips to research labs. One of them ended up with Stephen Fried who founded Microway in 1981 to create software for the 8087 and sell the chips, and the company is still in business after 44 years of chasing high performance computing. That's how I first got started with computing - a Microway Number Smasher (TM) card in an IBM PC.
The 80287 (AKA 287) and 80387 (AKA 387) floating point microprocessors started to pick up some competition from Weitek 1167 and 4167 chips and Inmos Transputer chips, so Intel integrated the FPU into the CPU with the 80486 processor (I question whether this was a monopoly move on Intel's part). This was also the first time that Intel made multiple versions of a CPU - there was a 486DX and a 486SX (colloquially referred to as the "sucks" model at the time) which disabled the FPU.
The 486 was also interesting because it was the first Intel x86 series chip to be able to operate at a multiple of the base frequency with the release of the DX2, DX3, and DX4 variants which allowed for different clock rates of 50MHz, 66MHz, 75MHz, and 100MHz based on the 25MHz and 33MHz base clock rates. I had a DX2-66MHz for a while and a DX4-100. The magic of these higher clock rates came from the introduction of the cache memory. The 486 was the first Intel CPU to utilize a cache.
Even though Intel had superseded the 8087/287/387 floating point coprocessor by including the latest version in the 80486, they introduced the 80860 (AKA i860) which was a VLIW RISC-based 64-bit FPU that was significantly faster, and also was the first microprocessor to exceed 1 million transistors.
The history of the FPU dedicated for special purpose applications is that it eventually became superseded by the GPU. Some of the first powerful GPUs from companies like Silicon Graphics utilized a number of i860 chips on a card in a very similar structure to more modern GPUs. You can think of each of the 12x i860 chips on an SGI Onyx / RealityEngine2 like a Streaming Multiprocessor node in an NVIDIA GPU.
Obviously, modern computers run at significantly faster clock speeds with significantly more cache and many kinds of cache, but it's good to look at the history of where these devices started to appreciate where we are now.
> The 486 was the first Intel CPU to utilize a cache.
The 486 was the first Intel CPU to integrate a cache on its die (following the competing Motorola CPUs MC68020 and MC68030).
Previous Intel CPUs already utilized caches, otherwise they could not achieve 0-wait state memory access cycles.
The cheaper 80286 and 80386SX motherboards usually omitted the cache to minimize the costs, but any decent higher-end 80386DX motherboard included an external write-through cache, with a size typically between 32 kB and 64 kB, so significantly bigger than the internal 8 kB write-through cache of 80486. An 80386DX without cache could never approach its advertised speed.
Because of the small internal cache of 80486, all good 486 motherboards implemented an external L2 cache, usually with sizes between 128 kB and 256 kB, as by that time the cost of cache memory chips had diminished in comparison with that of the years of 80386.
In the beginning, write-through caches were used, as they were much easier to implement externally.
Pentium (1993) was the first Intel CPU with a write-back cache (of 16 kB), which then was also added to the Intel 486DX4 CPU (100 MHz). Then AMD made 2 kinds of 486DX4 @ 100 MHz CPUs, an early model with an 8 kB write-through cache and a late model with an 8 kB write-back cache (which had also taken the CPUID instruction from Intel Pentium). AMD's DX4 @ 133 MHz had the write-back cache extended to 16 kB, like that of Pentium (and it was rebranded as 5x86, to confuse the buyers).
> The 80287 (AKA 287) and 80387 (AKA 387) floating point microprocessors started to pick up some competition from Weitek 1167 and 4167 chips and Inmos Transputer chips, so Intel integrated the FPU into the CPU with the 80486 processor (I question whether this was a monopoly move on Intel's part).
I don't think it was, transistor density became sufficient to integrate such a hefty chunk of circuitry on-die. Remember that earlier CPUs had even things like MMUs as separate chips, like Motorola 68851.
> I question whether this was a monopoly move on Intel's part
Well, I was happy about that because I no longer had to deal with switches to generated x87 code or emulate it.