Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!wuarchive!udel!princeton!njin!limonce From: limonce@pilot.njin.net (Tom Limoncelli) Newsgroups: comp.sys.amiga Subject: Re: Lies, lies, they're telling us lies... Message-ID: Date: 30 Nov 89 03:45:01 GMT References: <5003@nigel.udel.EDU> Organization: Drew University/NJIN Lines: 50 In article <5003@nigel.udel.EDU> acm131@eric.ccs.northeastern.edu (Craig Scott Lennox) writes: > Well, according to the IBM rep, there *is*. And this is one place where I > couldn't figure out if he was giving me a line of crap or not. But he said > that segmented architecture makes multi-tasking more efficient, because to > change context you merely reload the code, data, and stack segments. Instead > of copying the entire contents of page zero, out and in, etc. etc. Of ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > course, whe I pressed him as to why 8 Mhz Amiga 1000's with 512K can > multi-task better than his 33Mhz PS/2's he had no satisfactory answer, > but still... for future reference, I'd like to know, is this a legitimate > issue? Is there any multitasking OS that swaps between tasks/processes by swapping all of page 0? I can't think of any. Is this the technique that Mac's Switcher (is that what it's called?) or any of the similar programs for the Atari ST do? "Page 0" reminds me of "Zero Page" mode" like on the 6502. I remember Chris Lane (of Yale) published some code that permitted a VIC-20 to multitask. It swapped page 0, 1 and 2 (the stack) and the registers. It was so slow that rather than swapping every quantum, each program would have to SYS to a memory location once in their main loop. ( Now that I'm off the subject... ) He even hacked with the video chip to get a really bad split screen; each with a different program running. It was amazing! Each screen was at a different memory location and there was a interrupt driven routine that would switch which video buffer was being displayed at whichever starting scan-line. You couldn't predict when a IRQ would happen (in relation to the raster) so he did these crazy timeing loops and it flickered horribly. Ugh. But it was great to watch. Later when the Commodore-64 was shipping I was amazed because split-screens could be done as easily as writing a couple bytes of 6502 code. Is Chris net.accessible? Maybe we should have a vote for comp.sys.i.remember.the.vic.20? :-) Ok. I've rambled enough, -Tom -- Tom Limoncelli -- limonce@pilot.njin.net -- tlimonce@drunivac.bitnet rutgers!njin!tlimonce -- Drew University, Madison, NJ -- 201-408-5389 "All's well that ends well... if your a functional rationalist."