Mark Bult Design: San Francisco, CA, Established 1988

Web design and development for small and large business, e-commerce, b2b, b2c, SAAS, and community websites. User experience design and usability testing.

Monday, March 16, 2009

Opening DiskDoubler files from Mac OS 9

Back in the day
The first external hard drive I bought was a 40 megabyte SCSI device, and it cost about $400. That’s correct, 40 MB for $400. Today you can’t even fit Mac OS X (just the system, with no other program files) on anything less than several gigabytes, but in 1989, when I bought that home-assembled drive from a guy in Scotts Valey, CA, that was considered a pretty big drive. In fact it was big — physically at least; it measured about 12" by 3" by 5" — about the size of 12 DVD cases together.

Back then, most programs fit on an 800k floppy drive, and if you had data files bigger than 800k, you were really pushing the envelope with your computing. In 1988 through 1992, I was publishing Western Front News, and began to scan grayscale photos for the newspaper and impose them on Quark XPress pages for high quality digital output. This was cutting edge for the time, given that large metropolitan newspapers like the San Francisco Chronicle were still pasting up their pages by hand using paper, wax, and traditional halftone photos laid in by hand with hairline tape.

Grayscale images could make pretty big file sizes, however, and the layout program I was using to design the newspaper, Quark XPress, could make pretty big files too, unless you split your publication into separate files (e.g. “Front Page.qxd”, “Page 2-3.qxd”, etc.) which I did. But even using these tricks, files were beginning to get bigger than many people had space for, and hard drives were simply too costly for many people. This was also before removable solutions like Zip disks became popular.

Compression technology
Along came compression technology for the Mac like StuffIt and DiskDoubler, which used algorithms to look at the data in the files, close up gaps, and scrunch down needlessly duplicative parts (this is my vast oversimplification of how compression works). This was great for archiving files, but not very useful for files you were using all the time, since a file that had been DiskDoubled was unusable by the original creator program until you un-DiskDoubled it. Just like a ZIP file, which is what today’s modern OS X system uses for default compression.

After an edition of my paper was done and at the printer, I'd compress the Quark XPress files with Diskdoubler and then archive them on a few separate floppies. Then I could delete the originals from my $400 40 MB hard drive and free up a meg or two of space to work on other things.

DiskDoubler was great because you could enact it from the Desktop, which was uncommon then. You didn’t have to start it up each time you wanted to compress or uncompress a file, you could just select the file in the Finder and use a pulldown menu from the main Apple menu bar.

I was using DiskDoubler as early as System 6 and 7 (I think I bought it shortly after it was released in 1990), and I was definitely still using it as late as System 8 and 9. By the time I’d finally switched fully to OS X around 2002, DiskDoubler had been bought once or twice by other companies and future development had been shelved. I was still using it occasionally, but by then hard drives had become a lot more affordable, not to mention much larger in capacity.

Orphaned DiskDoubler files
It wasn’t until around 2006, when I bought a Mac Pro, that I realized I could no longer open these ancient archives I’d made in DiskDoubler. Until then, my trusty Mac G4 desktop could boot OS X and OS 9 at the same time, and while it wasn’t a perfect solution for using OS 9-only apps, there were so few instances that I needed OS 9 that it didn’t seem to matter.

The later version of OS X I had on my Mac Pro, on the other hand, did not boot OS 9. Now that I had this shiny new silver Mac and gigantic hard drives were pretty cheap (and I could fit up to four inside!), I’d moved most of my old files over from CDs and Zip disks and the like, thinking I could finally put old client files and other stuff in some logical order instead of having them all strewn all about. This would be especially helpful on those admittedly rare occasions when a client from ten years ago would call me up out of the blue and ask if I still had a map or logo or something (which happens about once every two or three years).

But even after ditching Zip disks and culling old files from CD-ROMs and putting them all on my Mac Pro, I still had lots of files that were .dd file format; they were DiskDoubled. In other words, I had files I couldn’t open. To make matters worse, I had about 100 floppy disks from waaaay back in the day, which contained some of my earliest client designs and most of my Western Front News archives. And all of those files were compressed using DD.

I had hung on to my older G4 for just this sort of reason. I knew it was the only way I was going to be able to open my old Quark XPress files, since I’d abandoned XPress long ago for InDesign and had no intention of purchasing the costly OS X version of XPress just so I could open ancient files that I only wanted to convert to PDFs.

I booted OS 9 and only then did I realize I’d never installed DiskDoubler on this Mac. I’d been using it at work, and I had it on an older Mac I hadn’t touched in years (and didn’t even have an extra monitor for). Not only that, I couldn’t find the program anywhere on my HDs.

The hunt is on
I tried every modern compression app I could think of, but none seemed to support DD format anymore (this was particularly disappointing of StuffIt, which used to be able to open DD files). I scoured the far-flung reaches of the Internets for a solution, to no avail. I saw random posts on various Mac help forums, people in the same boat as me, with age-old orphan files they wanted access to.

I eventually found one OS X program, The Unarchiver, that claimed to decompress DiskDoubler files, but it never worked. Finally, reading the developer’s support forum, I discovered that he just hadn’t gotten to implementing support for DD format yet.

Treasure found
At long last, yesterday I located an old backup CD of my utility applications from two or three computers ago. The CD is from 1999, but thank bog I held on to it, because it contained a working copy of Norton DiskDoubler Pro version 4.1, which runs under Mac System 9x and actually opens my Diskdoubler files. Hurrah!

A gift for those in need
As I mentioned before, I came across forum posts by other people trying to solve this same predicament over the years. Hopefully they’ll find this post via Google (I’ve tried to pepper the text with as many relevant SEO-able keywords as possible), and get some positive results from it.

Download Norton DiskDoubler Pro version 4.1 for Mac System 9

Recommendations for use
In order to use DiskDoubler you will need a Mac capable of booting OS 9.

The download file above is a ZIP archive made on OS X. You should download and unarchive it on OS X, then transfer the resulting folder to your Mac OS 9 volume (if you don’t have OS X and you can’t open the ZIP (I think you’ll be able to, though), leave a comment and I’ll see if I can use an older archive format).

On your OS 9 volume, open the folder Norton DiskDoubler Pro 4.1, and simply drag and drop any DiskDoubled file onto the application icon (see screenshot above). The file should compress to the same folder as the original, without deleting or moving the original. Those settings can be configured in the application, if you like.

Please comment
If you found this article helpful, have your own recommendations for using the app, or other advice to solve the orphaned DiskDoubler files problem, please leave a comment. If this article saved your life and you want to show your infinite gratitude by heaping mounds of money on me, please contact me directly and I will forward my offshore account info to you.

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Anonymous Anonymous said...

Thank you for taking time and detailing entire process, possibilities and surprises. This has been really helpful. Thanks once again.

4/24/2009 09:09:00 PM

Anonymous Anonymous said...

Hey thanks, you saved my life, or at least part of my digital life. Now I need to find that old mac with the "Classic" environnement enabled.

5/13/2009 11:18:00 AM

Blogger theninthplanet said...

Who'd have thought – 11 years later and the company wants to repress the cds – not their best sellers, not amongst my best work and absolutely not amongst my chosen listening but there you go... Disc Doubled files of course... once I'd managed to find the zip disc with them on. No DD on the Classic that runs on my ancient home back-up/emergency Mac, of course (abandoned ages ago) so... many thanks for bailing me out with that download. Sorry there's no offshore contribution but if you're ever in London... regards, Neil

6/17/2009 04:44:00 AM

Blogger Jefferson said...

I just retrieved a few thousand old files, thanks to this article. I had no idea I had left all those files DiskDoubled when I made one of my many Mac hardware upgrades over the years, and couldn't quite figure out what the problem was until tonight. Thanks!

7/10/2009 08:52:00 PM

Anonymous Anonymous said...

I had a diskette around with 4.1.1 on it and finally found it. If you install it on Classic, you probably will have to remove the DD Menu item from the Extensions folder.

In my case, it caused any attempt to access the Menu Bar to crash the Finder. Removing it solved the problem.

8/08/2009 08:05:00 AM

Anonymous Doug said...

Hi espd,

Thanks for your gift. I have unzipped the file and get DD Expand.sea. However, OS 10.4 thinks this is an application, not a Classic Application. Even though Classic is running, I can't expand DD Expand.sea to get the expander app itself.

Any suggestions?

8/11/2009 01:11:00 PM

Blogger espd said...


Just to be sure it wasn’t something wrong with my original file or directions, I did download the file and open it successfully on OS X.

I’ve seen what you describe happen before on other files of mine, and I think the problem is this: StuffIt or the OS X system-level Archive Utility (I’m not sure which was the culprit) seems to sometimes get confused about what to do with certain files when they’re downloaded and then automatically unzipped. It seems like it ends up making a self-expanding archive (.sea) of an already-zipped file.

I found that you can usually avoid this by saving the file to disk first, instead of clicking the link and having your browser automatically do whatever it’s set to do, which is usually to download and unzip without your intervention.

In Safari or Firefox, you’ll probably have to right-click or Command-click and select “Save link as...” (or similar language) to download the DiskDoubler file from this blog post.

After it’s downloaded, drop it onto StuffIt Expander. You may want to launch Expander first and check if it’s set to automatically make SEAs when files are dropped on it, which you should turn off.

If StuffIt Expander doesn’t work, try double-clicking to see if it launches the Mac’s Archive Utility. If that still doesn’t work, you might want to look for another free unzipping tool online.

8/11/2009 01:51:00 PM

Anonymous Doug said...

Hi. Thanks for replying. I had unzipped with Stuffit Expander. I finally got DD Expand.sea to expand, but don't know exactly which was the key:
1) Reset the type from APPL and back to APPL.
2) Removed the .sea extension.

After this, the kind changed from Application to Application (Classic) and double click on DD Expand expanded into the DD Expand 4.1 application. This may have been another symptom of OS X's metadata mis-design.

In any case, thanks again!

8/11/2009 02:11:00 PM

Blogger espd said...


It also might be that you’ve got Classic already running on the machine you’re downloading the file to. This might cause a conflict. I’d quit Classic before downloading and unzipping, then start Classic.

Actually, you probably have to download it on a machine that doesn’t have Classic installed on it, then unzip it and transfer it to the Classic machine, like the instructions I originally posted.

Now that it’s been a few months, I can’t quite remember why I had to do it that way, but I think a computer with the Classic environment on it will treat the file as a filetype that it’s not, and treats it as an SEA, rendering it unusable.

8/11/2009 02:13:00 PM

Blogger espd said...

@Doug: Glad you got it open!

@everyone: I hope other will share their own tips here too, if their experience differs from my instructions. Thanks!

8/11/2009 02:15:00 PM

Anonymous Anonymous said...

Wow! It works and I've got my files back (tons of WordPerfect documents I still can use that were compressed). I had to simply delete the DD Expand's .sea tag and it immediately worked in Classic 9.


8/26/2009 01:07:00 AM

Anonymous Mark Gelotte said...

I want to add my thanks to this. I had to open a lot of old FreeHand 3 files that were stubborn until I finally looked up their Type/Creator and saw DDAP (not FHA3). I completely forgot I used DiskDoubler back in 1992 on my old IIci... anything to save valuable disk space which was about the size of a CD today. Hard to believe.

I found your site and the downloaded file worked great in Classic mode.

Best, Mark

11/11/2009 09:41:00 AM

Blogger espd said...

I’m very glad to see other people are finding this helpful, and getting out of the predicament of orphaned DiskDoubler files. Cheers all!

11/11/2009 05:08:00 PM

Anonymous Anonymous said...

Using "The Unarchiver" is useful for many esoteric compression formats, including DiskDoubler. It's based on the modular libxad and is rather effective replacement for

1/12/2010 10:35:00 PM

Blogger SooBrett said...

You are a star! Thank you. I hadn't thought about those old files for ages ....but I've been asked to do some branding for a client from 1995 and I needed the legacy files.

I'm a huge Mac fan, been using them since my Mac SE with two floppy slots (!) in 1988. Still got it in fact: maybe it will be a collector's item one day.

But I do have a gripe about files becoming obsolete when you upgrade. I still haven't taken the leap to an Intel iMac because I can't afford to update all my software at the moment.

Thanks again. I can use this on my old PowerBook which still has OS9 installed.
Sue :)

2/08/2010 02:25:00 PM

Blogger Simon said...

In fact the current version of The Unarchiver works quite well. If you "get info" on your DD files and set the "open with" pane to The Unarchiver and also press the "change all" button then double clicking on any DD file automatically restores it to its unarchived form.

Opening Unarchiver allows you to set preferences.

Without an older Mac this has saved my day.


3/23/2010 12:59:00 AM


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