Back in the 90s, my home computer was an Acorn Archimedes. It had on it a piece of software called ArcFS, which allowed you to create compressed archives, a bit like zip files.

Unlike zip files, they could be mounted as a disk, a bit like dmg files on a Mac.

Unlike dmg files, they were compressed and writable.

If we could do this in the 90s, why can't we do this now? Today I use a Mac, and while I can create compressed disk images, they are not writable. Conversely, writable disk images are not compressed.

What is today's equivalent of ArcFS, and why isn't it more common?

  • 3
    Two words: Cheap disk. – Daniel R Hicks Jul 13 '12 at 11:41
  • One still has to wonder though, if we have enough CPU power to encrypt and decrypt on the fly, at least some compression shouldn't be an issue... – Daniel Beck Jul 13 '12 at 12:00
  • Arguably, compression on the fly could speed up disk access (at least with HDDs) - less actual disk activity for a file of the same size - assuming there's enough bandwidth available on the CPU/memory side of things. – Bob Jul 13 '12 at 12:30
  • @DanielBeck, this is true and, as you can see from the answers, compressed filing systems are alive and well. On both Apple and Windows, you can compress parts of the folder structure at will. Linux has a number of compressed filing systems along similar lines to ArcFS. – Julian Knight Jul 13 '12 at 12:33

I'm not sure which ones are available for Mac OS -- but there are still a lot of r/w compressed filesystems around:

  • e2compr being a kernel-patch for EXT2
  • Fuse offers a list of compressed filesystems, including such with r/w support like e.g. compFUSEd and LZOlayer_fs
  • Solid File Sysem is multi-platform (explicitly states support for Mac OS X) and supports encryption as well as compression

So it is still possible, and is still done. Why it is not more widely known, I cannot tell...


You don't say what version of Mac OS you are using but Mac's DO support compression natively - at least it has from Snow Leopard (10.6) onward. It's called "HFS+ compression".

For reference, there are several compressed file system for Linux and @kinokijuf has already mentioned NTFS compression.

So the world of compressed filing systems is still alive and well - it's just that, on Mac and Windows at least, it is now an embedded feature of the native disk formats.

  • Yeah I'm aware of this. There's a tool called Clusters that allows you to compress arbitrary files. But it's not quite what I had in mind, I specifically wanted something that was a portable archive file and could be passed around. – David Jul 13 '12 at 22:03

Windows NT has supported compression of individual files on NTFS volumes since version 3.51.

  • But that isn't Mac! – Julian Knight Jul 13 '12 at 12:25
  • Yes, I agree Bob - of course, as my answer shows - Apple do do it as well. ;) – Julian Knight Jul 13 '12 at 12:31
  • @JulianKnight The asker asked what happened to them, not if there are any on Mac. – kinokijuf Jul 13 '12 at 16:19

Two recent file systems, ZFS and btrfs allow to enable compression on read/write file systems. The file systems can be stored on disk files and mounted as such.

There is at least one open source project to support ZFS on MAC OS/X and also a commercial solution.


The other answers already point out that compressed FS still exist. As to why they are no longer popular - the main reasons are probably:

  • Disk space is quite cheap nowadays - many people I know never manage to fill their disks
  • Even if you run out of disk space on your main HDD, external storage is now much more practical to use. 20 years ago, all you had were tape and diskettes - now there are external harddrives, SSDs, big USB sticks, DVD-R/RW, which are both simple to use, reasonably fast, cheap and have high capacity.
  • If you do manage to fill up a disk, it is usually with audio/video data (music, photos, movies). These are usually already stored in compressed formats, so a compressed FS would not help.

Actually, I think the last point is the main reason.

  • 3
    Compression is still popular on modern file systems like ZFS. It is even often recommended to activate it with the latter as performance observed is usually better when enabled, as the I/O is the usual bottleneck and not the CPU. – jlliagre Jul 20 '12 at 10:32

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