Path: utzoo!attcan!uunet!cbmvax!daveh From: daveh@cbmvax.UUCP (Dave Haynie) Newsgroups: comp.sys.amiga Subject: Re: Mac ][ bashing / blitters are not everything Message-ID: <4516@cbmvax.UUCP> Date: 18 Aug 88 21:26:59 GMT References: <8808100909.AA00265@cory.Berkeley.EDU> Organization: Commodore Technology, West Chester, PA Lines: 36 in article <8808100909.AA00265@cory.Berkeley.EDU>, dillon@CORY.BERKELEY.EDU (Matt Dillon) says: > >>> -It doesn't multitask ... >>Funny, we run A/UX (Almost Unix) on our Mac-II and it multitasks ... > John, surely you have been following the various arguments on *THAT* > issue. The jist is essentially: You might be able to run an operating system > on some machine and get multitasking, for instance OS 9 on an Atari, but that > doesn't let you run all the old software under multitasking, does it. I.E. > the software under to original/standard OS. > -Matt And that's only part of it. If most users are single-tasking on a machine, there's a really good chance that not many hardware vendors are considering the hardware ramifications of multi-tasking. Which may mean that when you do start multitasking on such a machine, you may hit hard performance walls that never surface when you're single tasking. For example, consider hard disks. At least on some Macs (don't personally know about the Mac II), they handle disk I/O using a clever little hack that basically turns your data ready signal from the hard disk control chip into DTACK* for the CPU, so you read a full block just about as fast as possible with the CPU. Not all that bad for a single-tasking setup, as the program is sleeping during this transfer anyway. But come a multitasking OS, and all of a sudden this becomes a long atomic operation that takes a bite out of your performance. The standard Amiga hard drive controller is a DMA/FIFO combo that works better than interrupt or Mac-style I/O when you have the CPU sliced up amoung a number of tasks. -- Dave Haynie "The 32 Bit Guy" Commodore-Amiga "The Crew That Never Rests" {ihnp4|uunet|rutgers}!cbmvax!daveh PLINK: D-DAVE H BIX: hazy "I can't relax, 'cause I'm a Boinger!"