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From: gillies@m.cs.uiuc.edu
Newsgroups: comp.arch
Subject: Re: Macintosh OS (was: 68000 and Wo
Message-ID: <3300131@m.cs.uiuc.edu>
Date: 26 May 90 17:58:00 GMT
References: <402@newave.UUCP>
Lines: 41
Nf-ID: #R:newave.UUCP:402:m.cs.uiuc.edu:3300131:000:2108
Nf-From: m.cs.uiuc.edu!gillies    May 26 12:58:00 1990


> Can the Macintosh System be called an "Operating System"?  Ignoring
> system 7.0, the Mac is a collection of procedures, some of which are
> in ROM, that everyone agrees to call in the right order.  If anyone
> screws up, you get a bomb.  There is no real multi-tasking, no scheduler,
> no device or file locking, memory protection, processes, forking, etc.
> 
> What many people refer to as the O/S is really the finder program.  

The finder is a shell, not the operating system.  There is a very
beautiful paper by Butler Lampson, I believe, called "An open
Operating System for a Single-User Machine" (circa 82-84).  Basically,
Lampson observes that the advent of the personal computer allows us to
return to the golden days of the 1950's, with a single programmer, a
library, and a dedicated machine.  Apple's OS is a very close
approximation of lampson's ideal environment.

Some of the things that are important in a single-user operating
system are:
   1.  fast reboot ( < 10 secs)
   2.  no protected kernel, to allow easy modification of software
   3.  single address space, to maximize modifiability of software
   4.  automatic scavenger, to repair file system in case of harmful crash
 	(limited scavenging available on macintosh)
   5.  file system (mac file system has write-protect locking, by the way)
   6.  drivers (mac has half a dozen device drivers)
   7.  overlay loader (because early macs (& Alto) had no VM)
   8.  well-developed screen management package (window system, 
	vertical retrace synchronization), including picture language.
   9.  Ubiquitous protocol for serializing data on disk (in resources)
	(xerox CPUs use the courier data encoding format)

By these standards the macintosh system qualifies handsomely as an
operating system.  In fact, until NeWS was written, sun didn't even
have [8], and I wonder if it has [9]?  Maybe SunView does not qualify
as a single-user operating system. 8-)


Don Gillies, Dept. of Computer Science, University of Illinois
1304 W. Springfield, Urbana, Ill 61801      
ARPA: gillies@cs.uiuc.edu   UUCP: {uunet,harvard}!uiucdcs!gillies