close this bookTidBITS#92   19911111
View the documentMailBITS/11-Nov-91
View the documentCompression Corrections
View the documentProdigy Stumbles... Again
View the documentFar Side Calendar
View the documentReviews/11-Nov-91
View the documentFoot Notes

Compression Corrections

First, I asked Lloyd Chambers, DiskDoubler's author, about the conflict Murph had between the Quadra caches and DiskDoubler. Lloyd replied that there is indeed a problem that causes DiskDoubler INIT to crash in those circumstances. It was originally due to a bug in THINK C 4.0, apparently, and Salient has a fixed version (3.7.1) which they will send for free to anyone who is having trouble on the Quadra. There are no other changes in it.

Second, we inadvertently made some misleading statements in TidBITS-088/Compression II, and our apologies to Alysis (we already corrected the mistake we made about DiskDoubler and modification dates). We said, "DiskDoubler has safeguards (including working on a copy of the file and verifying the copy before deleting the original) against data-loss due to system crashes while compressing files. SuperDisk! does not have these safeguards for speed reasons, so if you regularly lose power, you should keep that in mind, or, if you're rich, buy an uninterruptable power supply."

After discussing this issue with Farokh Lam of Alysis Technical Support we can clarify the issue. SuperDisk! does keep temporary files in the System Folder for any files that it has open, so if you crash or lose power while opening or closing a compressed file, your file will be fine after you reboot. The important step here is rebooting. If you use MacsBug or the command-option-shift-escape trick to recover from a crash without rebooting, your file will appear to be corrupted if you look at it again immediately. Don't do it, just reboot, and SuperDisk! will do its magic with the temporary files and fix your file. Believe me, it works. I couldn't corrupt a file even with a fair amount of effort, which is testament to the efficacy of those temporary files.

There is a second situation which is more serious, but much less likely. If you lose power (a crash is extremely unlikely at this point) while SuperDisk! is compressing a file after you've renamed the file with a ".s" extension in the Finder, that file will be corrupted. The temporary files will not save you in this instance, but as Farokh rightly points out, the probability of losing power while compressing a file (especially since SuperDisk! is so fast) is very low. Murphy's Law of Lightning Strikes does apply, though. :-) Farokh also pointed out that if you regularly lose power, files corrupted by this unlikely occurrence will be the least of your problems and you should definitely buy an UPS. To quote from my favorite episode of Star Trek (and no, I'm not a junkie), "Right, Spocko."

Farokh was also kind enough to give me some glimpses into the features that Alysis has planned for SuperDisk! 2.0, which they hope to ship December 1st. Many of these additions address complaints we had in our review, so it will interesting to see how SuperDisk! 2.0 stacks up, especially since AutoDoubler and Aladdin's SpaceMaker should be coming soon too. Alysis has enhanced SuperDisk! so you can just add ".x" to a file to create a an auto-expanding file, which is good. They've tightened the compression, added checksums (which help ensure data integrity), and speeded up Finder file copies. The interface has been improved with the addition of menus, hot-keys, user-defined filename extensions (if you don't like ".s"), and new alerts. The animation is also gone, but they've added MS-DOS compatibility (in what form, I wonder?) and compatibility with DiskDoubler and StuffIt files. Farokh also assured me that Alysis is continuing to enhance the program all the time and upgrades past 2.0 will add even more impressive capabilities. Nothing like a little healthy competition to foster innovation. :-)

Information from:
Lloyd Chambers -- SALIENT@applelink.apple.com
Farokh Lam -- Alysis on AOL -- 72510.1317@compuserve.com