68000 & FPU

[Mac128]

Closing some gas in my understanding: How did the 68000 do complex mathematical calculations? Obviously both the Mac and Lisa had spreadsheet and graphics/CAD-type applications prior to the 68020 & 30. Did the software simply use the CPU to pull double duty? If so, then I guess the answer is s-l-o-w-l-y. In which case a Mac Plus, SE & Classic would have been unable to use later software which required an FPU ... would software FPU emulators run on a 68000?

 

[porter]

In which case a Mac Plus, SE & Classic would have been unable to use later software which required an FPU ... would software FPU emulators run on a 68000?

SANE - Standard Apple Numeric Environment

The first mac to use an FPU was the MacII, the first 68030 to not require one was the IIsi. Then there was the whole crippled 680LC40 thing.

68000s can't use many things including FPUs, virtual memory, anything past 7.5.5 etc.

The one thing they do have is preemptive threading with ThreadsLib.

 

[TylerEss]

s-l-o-w-l-y is the correct answer to this question. One can do floating-point calculations with a fixed-point CPU using special techniques.

I believe that one can emulate a full 68040 on the 68000 Macs by using available software: run 020 Simulator, then run Pseud040 and SoftFPU on top of that.

I further believe that to do so would be about as useful as Dana's stunt of booting MacOS X on the Q605.

 

[Bolle]

it was a C650

 

[Anonymous Freak]

Yeah, in school, I ran MacCAD on a dual-floppy SE. For simple 2D drawings, it worked fine. It didn't even attempt to do any 3d rendering, though.

For later classes with 3D rendering, we used IBM 386 PS/2s. Screen redraws of large drawings were painfully slow. We usually had our drawings in multiple 'layers', and turned off all that weren't absolutely necessary to the work we were doing right that instant. My senior year, the lab got one single 486. It was amazing. Incredible. Doing a screen redraw on a complex drawing only required 1 minute, instead of 10! (Today, even the most complex drawings we did back then would be so trivial, an iPhone could render it at many hundred frames per second.)

 

[Kallikak]

When writing mathematical software to run on a FPU-less machine, using fixed point rather than floating point for non-integer calculations usually results in significant speed improvement. This approach is well supported in SANE, but comes with some loss of precision.

Ken

 

[Mac128]

Ahhhh. SANE. Thanks, that's what I was trying to remember. It is ironic that the acronym suggests exactly the opposite of what such a ridiculously slow implementation of arithmetic processes would do to the human mind while waiting for a complex calculation to render.