If there is one subject that Mac users disagree on more than any other, it is automatic data compression — so much so that a recent issue of MacWEEK devoted a major story to the topic. Some professionals won’t touch it with a ten-foot SCSI cable, and others can’t live without it.
“It,” for those of you new to the subject, is automatic background data compression. Let’s look at that term in more detail. Data compression means smashing your data into a smaller space than it would normally take. This is valuable both for storage (on magnetic media) and for transmission (via a modem). Compression is accomplished by sophisticated methods of removing or coding redundant data. (It takes less space to say “437 zeros” than it does to say “zero” 437 times.)
There are two types of compression: manual and automatic. Manual compression is relatively straightforward; you use a compression program to convert files into “archives” which take up less space. Later, when you need access to the data in those files, you run the compression program again to “unstuff” the file, thus returning it to its original size and format. This procedure is valuable, but hardly handy; and it is most often used for files which are going into long-term storage, or which need to be transmitted via a modem.
Manual compression programs have been around for quite a while. Programs of this type which are currently popular for the Macintosh include Compactor Pro and StuffIt Deluxe. A more recent variation on the manual compression idea is represented by programs such as Disk Doubler and Magic Menu. These add a new selection to the Finder’s menu bar; simply select a file on your desktop, then choose “Compress” or “Expand” from the menu. This innovation removes the cumbersome need to run a separate program. Another benefit is that these programs allow for “semi-automatic” features; once you have compressed the file manually, double-clicking it will cause the file to automatically decompress, and its parent program will open it. After you quit, the file will be recompressed automatically. The only penalty you pay is the time it takes to decompress and recompress the file — usually just a few seconds, depending on the size and complexity of the original. Everyone seems to agree that these programs are completely safe.
The next — and current — step is fully automatic background compression, as exemplified by AutoDoubler 1.0, SpaceSaver, and More Disk Space. Once configured, these utilities sit in the background waiting for a time when your Mac is not busy (during a coffee break, for instance), and automatically scan your hard drive looking for things to compress. You, the user, can configure several aspects of their operation: what types of files to exclude from compression, how old files must be before being compressed, how long to wait before scanning, etc.) The beauty of these automatic compression programs is two-fold: first, you don’t have to manually compress files; and second, the decompression times are very short. (We haven’t been able to detect any speed difference between launching AutoDoubled programs and documents and their uncompressed counterparts. In fact, sometimes it seems as if the AutoDoubled files launch faster.)
The downside of automatic compression programs is the program conflicts that are inevitable with system extensions. Nobody denies that they exist, but most of them seem to have been resolved, at least with AutoDoubler. Still, a few obscure conflicts exist, and this makes some people very nervous.
Here at Mac Monitor, we’ve been using AutoDoubler since it first came out, and upgrading to each new version. We’ve never lost any data through its use. Our tests of More Disk Space, however, have shown it to be untrustworthy — at least on our system configuration — and we do not recommend its use, even though some users have reported no problems.
AutoDoubler 2.0
The latest version of AutoDoubler has recently arrived, claiming more speed, fewer conflicts, new features, and an improved interface. Since we experienced no conflicts with the earlier version, we cannot test the claim of improvement in this area. While the compression seems a bit faster, we found it impossible to accurately test this claim; background compression is, by definition, hidden from you. At any rate, we have no complaints in this area. As for the improved interface, we feel that, while largely cosmetic, it does help us to visualize the space usage on our hard drives. There is still room for improvement here. Using the Finder’s Get Info command on an AutoDoubler compressed file shows the size the file would be if it were not compressed. In order to find its real size, you must use also have DiskDoubler installed and use its “Savings…” command. (See illustration.)
The most visible improvements in the AutoDoubler package actually come from the “new features” which are contained in two separate programs included in the package: CopyDoubler and AutoDoubler Internal Compressor.
CopyDoubler, a Control Panel for System 7 users, serves several purposes. First, it allows normal Finder copying of files to proceed at up to three times faster, and can empty the trash up to ten times faster. Since System 7 is noticeably slow at these functions, these speed improvements are welcome.
CopyDoubler’s other function will be even more welcome to many longtime AutoDoubler users; it allows for easy copying of compressed files. With the previous version of AutoDoubler, copying a file from one disk to another caused it to automatically decompress. The idea was to protect you if you wanted to copy a file from your hard drive to give to someone else who might not have AutoDoubler. Many users exclaimed (loudly) that they did not want this form of protection since it was far more typical for them to move compressed files around for storage convenience rather than data sharing. CopyDoubler gives you the choice, and even provides a hot key setting to temporarily reverse the setting. CopyDoubler also includes a “Smart Replace” feature which can be a big help if you are copying a folder from one location to the other, by copying only changed files. This last feature, incidentally, may be helpful to PowerBook users who want to synchronize folders on two different computers. There are several settings which can be configured from the Control Panel.
AIC
AutoDoubler Internal Compressor has been supplied for advanced users. Some items do not function properly if compressed by AutoDoubler. This includes many INITs and Control Panels, as well as a few applications. Since many items in the System Folder should not be compressed, AutoDoubler automatically excludes it from compression. There are also some self-modifying programs which do not respond well to normal compression. AIC is provided as an optional way to compress internal resources in these files. AIC is a stand-alone program — it only runs when you manually launch it, and you decide how and where to use it. The manual gives complete instructions. AIC will allow you to compress some items which could not be compressed otherwise.
We tested different compression modes on two applications (FileMaker Pro and America Online) to compare their launch times. We could detect no difference whether the programs were compressed or not. (Of course, our precision lab equipment consisted only of a stopwatch.)
A New Scheme
Now that you understand different types of compression and decompression, get ready for a totally different concept. Golden Triangle has now released TimesTwo. All of the other products discussed here have been system extensions, which by their nature, alter your Mac’s operating system by applying patches to the System and Finder files. This is where the possibilities for problems and conflicts come in. TimesTwo is different in that it is a driver. As a hard disk formatter, it replaces the original formatter that came with your hard drive. TimesTwo compresses and decompresses all data as it is being written to the drive. The process is totally transparent — there is nothing to configure — and there should be no problems, as long as the driver is bug-free.
With TimesTwo, your hard drive will simply seem to be (approximately) twice as big as previously. A Syquest 44MM cartridge will hold over 80MB worth of data. Interestingly, you can take that enhanced cartridge to another Mac, and it will behave exactly the same as it did on your Mac. The driver is installed on the drive; there is no software that needs to be on the computer. This certainly sounded like the way to go.
Our first tests were somewhat confusing. We formatted a Syquest 44MB cartridge and attempted to back up our large System Folder onto it. Things seemed to be going well, but when we reached the point where the Finder thought the disk had approximately 50MB of data on it and about 30MB free, we started getting warning dialogs saying that the disk had less than 2MB of free space available. Our second attempt gave similar results; when we attempted to back up a huge folder of Type 1 fonts, TimesTwo began reporting disk full errors long before the Finder showed any concern.
A call to the tech support folks provided the answer: TimesTwo does not do a very good job of compressing fonts or the type of things one normally expects to find in a System Folder. Since TimesTwo shows the remaining free space on a disk as a guess of how much data it can hold, loading it with lots of hard-to-compress files threw its estimates way off. Golden Triangle recommends that you run its software from time to time in order to “verify” the disk. Each time we do this, we get a different estimate of the disk usage. Hopefully, each new estimate is more accurate than the last, but this seems an awkward way to ensure that the Finder gives a fairly accurate accounting of available disk space.
Our later tests — with more “normal” files — proved much more satisfactory; we formatted our old Jasmine 80MB drive, and it now shows approximately 170MB of usable space. We’ve added and erased files for several weeks with no problems. We tried another Syquest cartridge with TimesTwo for storing clip art with excellent results.
On our clip art cartridge, we got a compression rate of 1.956 to one, but on our font- and system-heavy cartridges, the compression was closer to 1.2 to 1 — not very good, but other compression programs either won’t handle the System Folder at all, or will handle it poorly. If you have huge amounts of fonts, nothing will help you very much. We have several hard drives, but we don’t try to compress our startup disk for this reason.
There are several other factors about TimesTwo that you might want to consider. If you use virtual memory, compressing the disk containing the VM swap file will cause serious performance hits. Also, the current version will not work with a partitioned disk, and the TimesTwo release disk seems to be copy protected in some way; normal copies of it do not function properly.
Conclusions
As stated previously, we’ve been using AutoDoubler since it first came out (and DiskDoubler before it). The IIfx in Mac Monitor’s office has three hard drives plus a Syquest attached to it, and since we’ve been testing TimesTwo (several weeks now), we’ve run one external hard drive with AutoDoubler, and the other (plus several Syquest cartridges) with TimesTwo. With the exceptions reported above, we haven’t had any problems. We’d be hard pressed to choose between the two compression approaches. AutoDoubler has the potential for INIT conflicts, but it has been around for a while, and it comes with CopyDoubler and the internal compression program. On the other hand, TimesTwo seems the best method in theory — (almost) total transparency and with no (known) conflicts. Even if you ultimately decide on TimesTwo’s approach, you’re likely to want to have a file compression program on hand to pack — or unpack — files for archival storage or modem transmission.
And remember, neither of these utilities guarantees that your disk space will be doubled. Different types of files compress differently. Our tests with TimesTwo, for instance, ranged from 1.956:1 to about 1.2:1, and we’d expect AutoDoubler’s performance to be comparable. As usual, there ain’t no such thing as a free lunch, but spending less than a hundred dollars for one of these “disk expanders” sure sounds better than spending several hundred dollars on a new drive. We hope we’ve given you the information you need to make the choice — and the courage to make the decision.
The article above is reprinted from Mac Monitor, the newsletter of The Savannah Macintosh Users Group. It may be reprinted in a single issue of newsletters published by non-profit user groups. Payment shall consist of a single issue of the newsletter in which the article appears, sent to the following address:
