Path: utzoo!attcan!uunet!wang!bu-tyng!three!cory From: cory@three.MV.COM (Cory Kempf) Newsgroups: comp.arch Subject: Re: Macintosh OS (was: 68000 and Workstations.) Message-ID: <327@three.MV.COM> Date: 30 May 90 04:00:00 GMT References: <30273@ut-emx.UUCP> <76700207@p.cs.uiuc.edu> <1990May24.114553.10301@phri.nyu.edu> <37@voa3.UUCP> Organization: Three Letter Co. Nashua, NH. Lines: 68 ck@voa3.UUCP (Chris Kern) writes: >For those of use who don't have any experience with the Mac OS, could >someone explain what its deficiencies are with respect to multitasking? >Is it that the OS doesn't do time-slicing? Does a context switch have >to wait for some event at the application level? How is multitasking >implemented? A few weeks ago, this would have been real easy... All I would have had to talk about was system 6.0. Now, (since I have gotten my mits on the alpha version of System 7) it is a tad more difficult. Background: In the beginning, there was the mac, a nice little single tasking desktop machine. Nice, but soon, people wanted more: Hence Switcher. Switcher was a system that would allow several applications to be around at the same time. Only one could execute at a time. Context switches were caused by the user (with co-operation from the program). Later, IBM announced that it was doing a brand new multitasking OS for its line of PCs. Apple, not to be outdone, announced that it would also. IBM/Microsoft decided that an abrupt change would be best. Apple decided that keeping their existing application base was more important, and decided to migrate to multitasking in three steps, each a year apart. They hoped to break less than 5% of the Applications at each step. The world of System 6: This is the first step. Cooperative multitasking was implimented, as were other things. A context switch occured when the application was waiting for the user to do something (the application was responsible for making timely calls to the OS to support this). If it didn't, background tasks were starved. While applications had to be specially written to support the multitasking, a properly written multitasking supporting application would run in the forground and the background seemlessly. Applications that did not explicitly support multitasking (in general) still allowed it to occur. Multifinder (The Multitasking version of the Mac's OS) broke on the order of 10% of the applications that worked in single finder. System 7: Well, Apple slipped a bit... What's a couple of years between friends? At this step, they have added Virtual Memory, two inter-processes communications systems, and some other goodies. One of the IPC systems is designed to allow say, a drawing program to create a picture, and, say a word processor, to paste it into the document. If the user should change the picture, the WP doc would be automatically updated. Apple has sent out an early release of the OS to developers in hopes of not breaking too many existing Applications. System 8: Like, vapourware to the Macs! :-) Supposed to complete the journey. Was due out (according to the original schedule) this year. From the rumor mill, is supposed to impliment preemptive time slicing, etc. +C -- Cory Kempf I do speak for the company (sometimes). Three Letter Company 603 883 2474 email: cory@three.mv.com, harvard!zinn!three!cory