This article is from the Miscellaneous Macintosh FAQ, by Elliotte Rusty Harold firstname.lastname@example.org with numerous contributions by others.
Symantec's Norton DiskDoubler Pro ($80 street, formerly known
as SuperDoubler) is a utility that automatically compresses and
decompresses most files on your hard disk so that you can store
more files on it than you'd otherwise have room for. As well as
transparently compressing files DiskDoubler can make self-extracting
and segmented archives for transmission via modem or floppy disk.
Ideally you won't know it's present once you've installed it.
Norton DiskDoubler Pro is a bundle of what was previously known as
AutoDoubler, Disk Doubler, and Copy Doubler, which are no longer
available separately. The consensus of the net is that DiskDoubler is
fast and safe.
Alysis Software's More Disk Space ($39 street) is a competing
product similar in functionality to DiskDoubler. More Disk Space
has several unique features that make it more suitable for use on
a network than competing products such as a freeware init that
allows all Macs to use files previously compressed by More Disk
Space as transparently as if More Disk Space itself were installed
and the ability to create a "compression server" that can compress
files for all Macs on the network on demand. Thus a network of
several dozen Macs could use one $39 copy of More Disk Space.
More Disk Space uses the fastest compressor/decompressor on the
market, but MDS also saves substantially less space than the other
products. More importantly More Disk Space relies on undocumented
features of the system which will go away in future system software.
I recommend against using More Disk Space.
The latest entry in the increasingly crowded compression arena is
QuickFiler, a portion of Now Utilities which takes the place of
the discontinued Now Compress. Now Utilities includes many other
features besides compression and is thus the best overall value
despite its $70 street price. The QuickFiler component of Now
Utilities offers automatic and on-demand transparent compression
plus archiving compression that's on a par with StuffIt's.
QuickFiler is fast enough that I don't notice it's installed (as
is DiskDoubler) which is the point where I decide it's not worth
my effort to run detailed timing comparisons. QuickFiler does
compress tighter and thus save more space than any of the
competing products. Furthermore it's the only file-level program
that will transparently compress almost anything in the System
Folder. It's as fast or faster than its competitors; and
it frees up more space on a typical hard drive than any
At about half the price of Now Utilities or DiskDoubler,
SpaceSaver ($35) from Aladdin Systems is also a good value,
especially since it can create and expand net standard .sit files
thus serving both archiving and transparent compression needs. The
compression is fast although it's not as tight as the competition's.
SpaceSaver does give up some speed by decompressing applications onto
disk rather than straight into RAM like other compressors. This may
improve compatibility with future systems but slows decompression and
contributes to file fragmentation, especially on very full disks.
Documents normally need to be decompressed onto disk regardless of
compressor, and SpaceSaver is faster than most for compressing and
decompressing documents. SpaceSaver has some minor incompatibility
problems with System 7.5.1 and 7.5.2 (but not 7.5.0 or 7.5.3).