Mac OS X 10.3.5 brings new update variations

[Since our initial posting of this article on Wednesday, we've added a couple significant updates; see the end of the article for details.]

Prior to the Mac OS X 10.3.5 Update, Apple generally released two versions of each Mac OS X update: a "standard" update and a "Combo" update. The standard update only updated the previous version of the OS to the current version; for example, the standard updater for Mac OS X 10.3.4 could only be used to update Mac OS X 10.3.3. The Combo update, on the other hand, could be used to update any minor version of the OS to the latest, meaning the Mac OS X 10.3.4 Combo update could be used to update OS X 10.3.0, 10.3.1, 10.3.2, or 10.3.3 to version 10.3.4. Standard updaters could be downloaded either via Software Update or Apple's website, whereas Combo updates were only available from the website.

With the release of Mac OS X 10.3.5, Apple has quietly renamed the standard updater "regular-sized Delta" and implemented a third type of updater, the "smaller-sized Delta." Here are a few excerpts from Apple's Knowledge Base article on the topic:

Sometimes, Software Update preferences is able to offer a "smaller-sized Delta" update than you might expect, or smaller than what you might see on other computers installing the same update. The "smaller Delta" updates are offered when some Mac OS X system files can be modified instead of replaced in their entirety...Smaller-sized Software Updates take less time to download and install than regular-sized Delta or Combo updates.

Why are some computers not offered a smaller update? Not every computer that has Mac OS X 10.3.4 or later can benefit from smaller Software Updates. Why? Sometimes, modifications made to Mac OS X system files, including ones made by third-party products, may require the installation of a full sized version of a Mac OS X software update. Again, you don't have to worry about figuring out which kind of update is best for you, just let Software Update preferences do the work.

The result is that for Mac OS X 10.3.5 there are now three versions of the OS update:

1. "Patch" update (officially known as the "Smaller-sized Delta" update): This update (23MB in size for OS X 10.3.5) does not contain the complete versions of all files/packages to be updated; it only contains those resources that need to be changed. It is only available for updating the immediately previous version of OS X, and even then only if the files/packages to be updated have not been modified or removed. Patch updates are only available through Software Update.
2. "Standard" update (officially known as the "Regular-sized Delta" update): This update (43MB in size for OS X 10.3.5) contains the complete versions of all files/packages to be updated. It is only available for updating the immediately previous version of Mac OS X. Stadard updates are available for manual download from the Apple website and -- if Software Update determines that your computer cannot use the patch version of the update -- via Software Update.
3. "Combo" update (officially known as the "Combined Update"): This update (88MB in size for OS X 10.3.5) contains the complete versions of all files/packages to be updated, as well as all updated files/packages from all preceding updates to your version (10.2, 10.3, etc.) of Mac OS X. Combo updates are available for manual download via the Apple website and -- if Software Update determines that your computer cannot use either of the Delta updates -- via Software Update.

We're assuming that this approach will also be used for future OS updates.

(If you've already installed the OS X 10.3.5 Update and you want to see if you installed the new patch version, open the /Library/Receipts folder on your hard drive. If you have a receipt package called "MacOSXUpdate10.3.5Patch.pkg," you installed the patch update.)

What this means for users The availability of this new patch update format has a few consequences for users:

• Updating multiple Macs If you have multiple Macs/PowerBooks/iBooks, in the past many users would download OS updates via Software Update and then use that update package to install the update on all of their computers. As long as all those computers were running the immediately previous version of OS X, this approach worked fine. However, with the introduction of patch updates, it's possible that a patch update package downloaded on one computer may not properly update another computer (for example, if the latter requires the standard update). There are two workarounds for this. The first is to run Software Update on both computers to view available updates; if the version of the Mac OS X Update (shown in the information panel at the bottom of the Software Update window) and the size of the update (shown in the Size column) are identical, you should be able to download the update on one computer and use it to update both.

  The second approach -- which is the one we recommend -- is to simply download the Combo updater from Apple's website and use that package to update all of your Macs. This procedure is safer, since it doesn't make any assumptions about what has previously been installed or modified, and, based on our experiences, is a better approach overall, since it updates every file from all previous updates.

• "Installing" individual files from update packages A common (perhaps too common) approach to troubleshooting certain problems is to use a utility like Pacifist to extract individual files from Mac OS X installers or updates and then use them to replace (presumably damaged or otherwise problematic) existing files. We've warned readers in the past that this procedure can be dangerous if the update package does not contain the complete package (for example, an OS X Update may contain particular files from the iPhoto application package, but not the complete application). The new patch update format is especially dangerous in this respect, as you're almost assured that this version of an OS Update does not contain complete packages.

  If you're determined to use such a procedure to extract files from an OS X Update, do not use a patch update; in fact, we don't even recommend using a standard update. Instead, download the latest Combo update and extract files from that package.

UPDATE We've received a note from a reader, Stephen Northcott, who found that the "patch" update package will not work on a different model than the one on which it was downloaded:

"When I tried to install the Patch update that worked on my PowerBook G4 17" on my Power Mac G5 it told me that it was not an allowable update and I have consequently had to download the whole 88MB update for my G5."

So apparently "patch" updates are, at least in some cases, machine-specific.

UPDATE #2 Several readers have reported that on their systems, Software Update is listing the Combo update (88MB) as the only 10.3.5 Update available. It appears that if Software Update determines your installed system cannot be updated with either of the "Delta" updaters, the Combo update will be used instead.

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