New Directions for the Macintosh Operating System

Albert Willis

Apple Computer has announced that the current version of the 
Macintosh Operating System - 7.5.5 - will be the last to support Mac-
intoshes without 32-bit clean ROMs. Models that are not 32-bit clean 
include the Mac Plus, SE, SE FDHD, Classic, Portable, PowerBook 100, II, 
IIx, IIcx, SE/30, and LC.

Before considering the implications of Apple's announcement, it's 
worth understanding what being 32-bit clean is all about.

Being Clean
The Macintosh ROM (Read Only Memory) contains a series of routines 
known as the Memory Manager. Software written for the Macintosh calls 
the Memory Manager to get memory for its use.

The original Macintosh was based on the 68000 microprocessor. While 
the 68000 was a 32-bit microprocessor - it used 32 bits for every memory 
address - it physically had only 24 address lines. This meant that only 
24 of the 32 bits were meaningful. Apple's Memory Manager took advantage 
of this fact by using three of the unused bits to keep track of the 
status of memory blocks. Creative third-party programmers used the 
remaining five bits for their own purposes.

When System 7.0 was introduced in 1991, it came with a new version 
of the Memory Manager that used all 32 bits of a memory address. 
Programmers who wanted to be fully compatible with System 7.0 had to 
make their programs 32-bit clean - clean in the sense that their 
programs didn't make use of any bits of a memory address.
 
System 7.0 was the first Macintosh Operating System (Mac OS) that could 
address more than 8 MB of memory - but only if 32-bit addressing was 
turned on. A software company called Connectix created Mode32, a utility 
that allowed some non-32-bit-clean Macintoshes (II, IIx, IIcx, and 
SE/30) to run in 32-bit mode. Models with older ROMs (Mac Plus, SE, 
Classic, and Portable) don't support Mode32. 

Implications
Although some users may feel left behind by Apple's announcement, 
Apple has actually supported older hardware a lot longer than most 
vendors do. It's almost unheard of for a company to release system 
software like 7.5.5 that still runs on machines that were manufactured 
ten years ago.

By developing system software only for machines that are 32-bit clean, 
Apple will be able to make future versions of the Mac OS more robust. 
This strategy also paves the way for features that have been in the 
planning stages for a while.

These changes in direction won't have any noticeable effect for some 
time. Software that works on older Macintoshes will continue to work, 
and software developers will continue to support these machines in the 
short term. However, as time goes on, developers will gradually drop 
support for older Macintoshes. Microsoft has announced that the next 
version of Office will run only on PowerPC-based Macintoshes, for 
example.

Consequences on Campus
In addition to the issue of developers gradually dropping support for 
older Macintoshes, newer components of the Mac OS are critical for 
running some widely used applications on campus. The SAP financial 
system and Tether dialup service are two applications that require newer 
system software components in order to run on Macintoshes connected to 
MITnet.

For security reasons, SAP requires a software component called Code 
Fragment Manager (CFM). CFM has been part of the system software of all 
Power Macintoshes, but is optional for 680x0 machines. CFM requires a 
68020 or greater processor, System 7.1 or higher, and 32-bit addressing 
turned on. This means that SAP will never be able to run on machines 
with 68000 processors (like the Plus and SE), and that machines which 
aren't 32-bit clean may not be able to run SAP securely.

Open Transport, Apple's new networking software, has requirements 
similar to CFM, except that it requires a 68030 or greater processor 
to run. Open Transport will be required by Apple's new Point to Point 
Protocol (PPP) client, which IS will use in the near future to support 
its Tether service. While older versions of the PPP software will 
continue to work for older Macintoshes and the Tether service, the third 
parties who developed the PPP programs are no longer actively supporting 
them.

What To Do
Macintosh managers and users on campus need to start evaluating their 
current situation with respect to 68030 and earlier Macintoshes (roughly 
six years or older). It's important to assess how many of these machines 
a group or department has, and what they are being used for.

If you have older Macintoshes that are being used to perform 
Institute business, and you expect to make the transition to new 
applications such as SAP, it's time to start planning for new machines.

Information Systems is working on guidelines for when you should upgrade 
or continue to use your existing Macintosh models, depending on their 
typical application use. That document should be available by the time 
you read this article. For more information, including the latest 
Macintosh recommendations from IS, check the Web page at

http://web.mit.edu/desktop/ 

If you'll need to buy new equipment, the good news is that all 
Macintoshes based on the PowerPC chip (both Power Macintoshes and 
clones) will run current and future operating systems from Apple and 
support CFM and Open Transport. SAP and connection software for the 
Tether service will also run smoothly on PowerPC machines.

Now and Near Future: 7.5.5. and 7.6
As was mentioned in the previous issue of i/s (Sept./Oct. 1996, page 
4), System 7.5.5 is an update for users who are running System 7.5.3. 
The update is available from Apple's various ftp sites, as well as 
the CSS File Server in the IS-CSS AppleTalk zone; the path is 
Public:AppleSoftware: SystemSoftware:System 7.5.5 Update.
 
The planned January 1997 release of the Mac OS (version 7.6) will run 
on all Macintoshes except for the ones mentioned at the beginning of 
this article. System 7.6 consolidates several components that have been 
available separately, such as OpenDoc and Cyberdog. It will also include 
the latest versions of QuickTime, QuickDraw 3D, Open Transport, and Open 
Transport PPP, Apple's PPP client.

Concerns
If you have questions concerning Macintosh system software and supported 
models, contact the Computing Help Desk at <computing-help@mit.edu> or 
x3-0001.