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Mac OS 9 Installation & Compatibility

Apple has released Mac OS 9 with fanfare, billing it as "the best Internet OS ever" and touting more than 50 new features. Some of these features add significant new capabilities (like file sharing over the Internet, encryption, support for multiple users, and automatic software updating via the Internet); other features mark the return of old ideas (the Keychain password management tool, a Sound control panel, and flexible PlainTalk speech recognition); and still other features are extensions of previous enhancements, like the almost unrecognizable Sherlock 2. Under the hood, Mac OS 9 makes some fundamental changes that may break some of your applications but will also be welcome to anyone pushing the limits of what their Macs can do.


Pricing & Requirements — Apple officially began selling Mac OS 9 23-Oct-99, so it’s available now to U.S. and Canadian customers from Apple and virtually all Macintosh software retailers for U.S. $99 or less, such as the $70 after-rebate deals from TidBITS sponsors and Small Dog Electronics (who throw in a pint of Ben & Jerry’s ice cream). Apple and those same retailers have been accepting pre-orders for months, so if you’ve already purchased Mac OS 9, your copy should arrive shortly. Apple says international versions of Mac OS 9 will be available in November.

If you purchased the Mac OS – either on its own or with a new computer – after 05-Oct-99, you may be able to upgrade to Mac OS 9 for $20. Owners of Mac OS 8.5 or 8.6 may qualify for a $20 mail-in rebate from Apple; details are inside the Mac OS 9 box. Unfortunately, both these offers are available only to U.S. customers.


Mac OS 9 requires a Macintosh with a PowerPC processor, at least 32 MB of physical RAM (though 48 to 64 MB of RAM is a more reasonable minimum), and 150 to 400 MB of free disk space depending on selected options. Apple has not certified Mac OS 9 for use with Macintosh clone systems or on systems using third-party processor upgrades, although it may work. Folks with third-party processor upgrades should check with the upgrade manufacturer before trying to install Mac OS 9.

Installation — Installing Mac OS 9 is self-explanatory, but is best done by booting from the Mac OS 9 CD-ROM – installing Mac OS 9 while booted from other disks almost always proceeded correctly in my tests, but sometimes with unexpected alerts and errors. As always, make a complete backup before attempting to install Mac OS 9. If you use third party hard disk formatting utilities like La Cie’s Silverlining or FWB’s Hard Disk Toolkit, check to make sure your hard disk drivers are compatible with Mac OS 9 before installing.

In general, Mac OS 9 wants more memory than previous versions. Starting up with extensions disabled, Mac OS 9 uses about 18 MB of RAM. With reasonable extensions, the system software could balloon up to 30 MB with virtual memory turned on; without virtual memory it could require as much as 10 MB of additional RAM.

Apple’s Language Kits are included in Mac OS 9; they were sold separately for earlier versions of the Mac OS. If you’re using one of the kits (Arabic, Cyrillic, Japanese, etc.) be sure to perform a customized installation of Mac OS 9 that includes the Language Kit you were previously using – otherwise it will not be updated. Also check the Language Kits CD Extras folder on the Mac OS 9 CD-ROM for localized versions of SimpleText, fonts, and utilities.

FCBs & Compatibility — Mac OS 9’s file systems includes two significant under-the-hood enhancements: one allows applications to open files larger than 2 GB; the other increases the maximum number of open file forks from 348 to 8,169. Opening 348 file forks simultaneously might seem unusual, but both the problem and the fix turn out to be significant. The limit predates even the HFS file system, and it’s a problem because a typical Mac has many open files you never see: modern applications and versions of the Mac OS rely heavily on shared libraries, temporary files, and plug-ins – all those items count against the open file limit. Plus, we all know people with hundreds of fonts and sounds.

To allow more open files, Apple had to change the file control block (FCB) table the Mac OS uses to track open files. Apple has been warning developers not to access the FCBs directly since 1986, but few developers took Apple seriously because Apple had never revised its own code. So long as Apple software depended on unapproved methods, developers figured their programs could depend on those same methods.

The resulting situation was a mess, and Apple couldn’t find a way to increase the number of open files and retain compatibility with widely deployed code. So, in Mac OS 9 Apple instead prevents that code from running and possibly crashing the system or corrupting data. Whenever a program tries to use unsupported methods for accessing information about open files, Mac OS 9 shuts down the application with an error number 119, and displays a dialog saying you need an updated version of that application. It’s annoying.

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What’s more annoying is that many commonly used applications and utilities need updating – I’ve included a partial list of major problems below. Disk tools, file utilities, font management tools, and anti-virus software are especially likely to be impacted. Alsoft has released a checker that can inspect PowerPC applications for compatibility with the Mac OS 9 file system – it produces an HTML report you can view in a Web browser. I can’t vouch for its results, but it could prove useful.

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  • Versions of Adobe’s ATM and ATM Deluxe prior to 4.5.2 are incompatible with Mac OS 9, and the Mac OS 9 installer automatically disables them if present. Versions of Adobe Type Reunion prior to 2.5.2 are also incompatible. Adobe has released updates to these utilities for use only under Mac OS 9; keep in mind that Type 1 fonts still print correctly without ATM and current versions of some Adobe applications (such as Acrobat and InDesign) no longer require ATM to rasterize PostScript fonts on screen.


  • New versions of StuffIt Deluxe and the StuffIt Engine compatible with Mac OS 9 ship on the Mac OS 9 CD-ROM – be sure you install the Internet Utilities. StuffIt Deluxe and components of Private File are not compatible with Mac OS 9; Aladdin expects to ship an update to StuffIt Deluxe soon.


  • RAM Doubler 8 is reportedly incompatible with Mac OS 9; Connectix expects to have an update available in Jan-00.

  • Drivers for several Hewlett-Packard DeskWriter and DeskJet printers are incompatible with Mac OS 9; HP says it will update its drivers for compatibility.

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  • AppleWorks must be updated to version 5.0.4 to work with Mac OS 9; an updater is on the Mac OS 9 CD-ROM.

  • Netscape’s TalkBack Quality Feedback Agent – which might be present with Netscape Communicator 4.5 or later – is incompatible with Mac OS 9. You can remove the TalkBack folder from Communicator’s folder.

  • If you use MacsBug, Apple’s low-level debugger, you’ll need to obtain version 6.6f2c1 for use under Mac OS 9.

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As always, there may be additional compatibility problems related to upgrading to Mac OS 9, particularly if you haven’t been staying up to date on all of your software. Until you’ve become comfortable with the stability of Mac OS 9 for your particular uses, save often and back up religiously.

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