Toby Thain wrote: > On 2017-01-24 2:46 PM, Jecel Assumpcao Jr. wrote: > >[PC emulator on ARM emulator on PC] > > Was this a JIT emulator (like Apple's later versions of 68K emulation), > or a simple interpreter?
It was a simple interpreter. I had been aware of the 1984 JIT implementation of Smalltalk by Allan Schiffman and L Peter Deutch. The goal was to test the worst case, however, and that was the interpreter. Note that the PC emulator was incomplete - it only had enough code to correctly run the benchmark programs. That made us miss the most serious bottleneck, which is the correct emulation of all the 8088 flags (specially the parity flag and the auxiliary flag). I have heard that Dave Ditzel was looking at emulating the PC on the Sparc at Sun and figured out that adding a tiny piece of hardware to calculate these flags would nearly double the performance of the emulator and that this was one of the inspirations for Transmeta. Pete Turnbull wrote: > Interesting. You know that Acorn had a software PC emulator for the > Archimedes called PCEmu, on sale in late 1987? In 1988 they sold it > bundled with an Archimedes A310 (8MHz ARM2, 1MB of RAM) called the A310M > (M for MS-DOS). It ran at just a little less than the speed of a > 4.77MHz 8086. I don't remember if I was aware of this at that time, but it is very likely and that could have been the inspiration for our project. Note that we did all our own tools even if Acorn was selling them to their customers. In the RiscPC era they used actual Intel processors instead of (or was it as an alternative to) software emulation. > Amusingly, it ran MS-DOS better than the then-current > Nimbus PC from their arch competitor Research Machines - PCEmu would > happily run things like Borland Sidekick, Lotus 1-2-3, Microsoft's > Flight Simulator etc where the RM PC often failed because it had a > custom MS-DOS running on an 80186. Many people think Intel was stupid to have the 80186 be incompatible with the PC but they forget that this processor was practically finished by the time the PC came out and was launched just a few months later, which is long before the importance of the PC became obvious. Even with the 8088 there were plenty of MS-DOS machines that were not PC clones for about two years before clones became the standard. -- Jecel
