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ATPM 4.09
September 1998




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The Personal Computing Paradigm

by Michael Tsai,

Disk Copy—Not Just For Floppies

We take it for granted, but Mac OS does a great job of handling floppies. From the beginning, the Mac could identify which floppy was which, then ask you to insert the proper one by name. (Okay, so maybe you don’t have fond memories of swapping floppies...) Until recently, Macs had auto-inject floppy drives—that is, the drive could help you out by “pulling in” the disk. And, of course, Mac users have never needed to worry about ejecting floppy disks. There isn’t even an eject button; the operating system “knows” how and when to eject floppy disks.

Then, there are the details that we take for granted but people in the Windows world cannot. The Mac knows when you insert a floppy disk. (In fact, there is even a special “event” to let Mac programmers know that a floppy has just been inserted.) Mac OS automatically displays the floppy’s icon on the desktop (complete with an IBM-striped “PC” if the floppy is DOS-formatted or a six-color “II” if it’s ProDOS formatted). No need to locate the “A” drive and “refresh” it. If a floppy disk is ejected, its contents are grayed out; trying to open one of its files then asks you to insert the floppy (rather than summoning a cryptic error message)—all part of the Mac’s polish.

But Floppies Are Dead...

That’s right. With iMac, Apple is effectively saying that floppies are on their way out. The lack of a floppy drive is the iMac’s single boldest “feature.” (Hey, it is documented.) Soon, the few pieces of Mac software that still ship on floppies will switch over to CD-ROMs. For software distribution, this is great. Floppies are notoriously unreliable and slow. (Remember the days when the first step in installing a piece of software was backing up the master floppies?) Though the road to a floppy-less world is likely to have a few ruts, I, for one, am glad we’re finally moving in that direction.

Where does this leave Apple’s Disk Copy utility? Actually, it’s more useful now than ever. You can be sure that it’ll come in handy for installing software shipped on floppies onto the iMac.

DiskCopy—Apple’s 3.5" Disk Duplicator

[pcp2 graphic]Since the late ’80s, Apple has provided a free utility called DiskCopy for Macintosh users. DiskCopy can turn floppy disks into disk images—files containing the complete contents of the original floppy disk. After acquiring a disk image from a CD-ROM, online service, or wherever, you could use DiskCopy to make a floppy identical to the original. DiskCopy could make multiple copies of a single floppy disk. It also used a CRC (Cyclic Redundancy Checksum) to insure that duplicates were exact copies of the original.

[pcp3 graphic]

The playing field was made more interesting by the fact that there were numerous competing formats for disk images—Apple’s DiskCopy, Apple’s DART (Disk Archive/Retrieval Tool), Symantec’s Floppier, Central Point’s FastCopy, and shareware formats like DiskDup+ and ShrinkWrap (now published by Aladdin Systems). Though some utilities could read other’s formats, disk imaging was complicated: conversion utilities abounded, and there was no real standard. Sure, Apple’s DiskCopy was the most ubiquitous, but it was also probably the least desirable to use.

Probably the most common use of disk images was for distributing Apple system software (In those days, Mac OS updates were free to all Macintosh owners). After downloading a disk image over AppleTalk or a modem, the last thing you wanted to do was copy the image from a fast hard disk to a slow floppy—then install the software from that slow floppy.

Mounting Images

Thankfully, there were separate utilities that let you “mount” images on the desktop. The images could then be manipulated just as though they were real floppy disks. Of course, there were scads of image mounting utilities as well—Mount Image, Drop*Disk, Mt.Image, and ShrinkWrap are the ones still in the Utilities folder of my hard disk. Often, images would be created with one program and mounted with another.

Disk Copy 6.3

[pcp4 graphic]Today, the landscape is a bit different. Although the programs mentioned above still exist, Apple’s Disk Copy (now with a space in its name) and Aladdin’s ShrinkWrap are the disk imagers of choice. ShrinkWrap offers more options, but is a commercial application. Apple provides Disk Copy for free at: This Site

Disk Copy 6.x offers a number of improvements over previous versions. With the NDIF (New Disk Image Format), just about any type of volume can be imaged: floppies, CD-ROMs, hard disks, folders. In addition, it can use Apple’s PlainTalk speech synthesizer to speak dialogue text to you (useful if you are across the room when a lengthy imaging operation encounters an error) and is much easier to use than previous versions.

Read-Only Compressed Images

Read-Only Compressed images work just like normal read-only images, only they take up a fraction of the space. (Note: Though decompression takes place quickly and transparently, compressing can be very time-consuming.)

In general, Disk Copy does not compress as tightly as Aladdin’s StuffIt. However, it does offer several significant advantages, which is why I now use it in place of StuffIt for many of my compression needs. Using a compressed image is a one-step process. Just double-click the image, and it mounts just as though it were an uncompressed image. StuffIt archives must first be decompressed. This means that if the archive is 50 MB and the uncompressed folder is 100 MB, you will need in excess of 150 MB to decompress and use the archive. Since Disk Copy decompresses “in place” you might need only 60 MB for the image (since Disk Copy doesn’t compress as tightly as StuffIt.)

A great use for this feature is making images of CD-ROMs. Because of compression, the image may take only 300 MB or so, for an entire CD. (Yes, 300 MB is still a lot, but these days, most machines ship with 4 GB hard drives, only a fraction of which many people use.) This is useful for using software that requires a CD-ROM on a PowerBook that doesn’t have a CD drive (or to save battery power and space even if you do have a CD-ROM drive). I’ve even heard of people making disk images of CD-ROMs so their (young) children can run their favorite games with only a few clicks of the mouse.

Easier Than Conventional Compression

Aside from allowing you to work with larger images/archives that StuffIt (for the same amount of hard disk space), Disk Copy allows you to work with small images/archives far more elegantly. With StuffIt, an archive is either compressed or expanded. If you want to selectively decompress files in an archive, you must use a separate utility (StuffIt Deluxe or StuffIt Lite) or Aladdin’s True Finder Integration control panel (part of StuffIt Deluxe), which lets you work with archives in the Finder as though they were folders.

With Disk Copy images, all you need is the Disk Copy application. And, in fact, if the image is self-mounting, you do not even need that. Among other things, this means you can easily put a collection of images on a recordable CD or read-only network volume. The images’ contents can then be accessed with a simple double-click—no extra extensions, applications, or even hard disk space required.

Read/Write Images

Disk Copy also lets you work with read/write images. These behave like “soft” partitions and have a number of uses. First, it is often convenient to work with many small files as one large file. This makes Finder manipulation faster. In addition, the imaged files only “clog” Find File results if the image is actually mounted. More importantly, creating a read/write disk image can be a great way of saving disk space because the minimum file is directly related to the volume’s size.I have also found read/write images useful for applications that depend on path names to locate files. For instance, if a collection of Excel files need to reference each other, it is often convenient to place them all in a disk image. This shortens the paths to the files (making links easier to edit in Excel). Furthermore, since the “disk” the files are located on is actually an image, you can then copy the image file to other computers without worrying about links breaking because disk and folder names have changed.

Images of Floppies

If all you want to use Disk Copy for is working with real floppy disks, you’ll be pleased to learn that it still does an excellent job of copying floppies. In fact, you can even use it to mass-format floppy disks. Just format the first disk in the Finder. Name it and position its window however you like, then use Disk Copy to duplicate it.

Disk Copy Extras

[pcp5 graphic]So far, nearly everything I have described is easily accessibly from the Disk Copy application. (There are a myriad of ways to accomplish each disk image operation: menus, drag-and-drop with modifier keys, etc. I recommend reading the Disk Copy manual to find the way that works best for you.) Additional feature are available via AppleScript and Disk Copy DiskScripts.

Don’t worry; there’s no need to learn AppleScript just to make self-mounting images. Apple has pre-made some scripts for configuring floppy insertion preferences, creating self-mounting images, and segmenting images.

There is also a contextual menu plug-in that lets you access common imaging functions.

Click here to download.

If you create a folder called “Scripts” in the same folder as Disk Copy, the contents of that folder will be available in Disk Copy’s Scripts menu. If you are the AppleScripting type, I think you’ll find Disk Copy’s dictionary powerful and easy-to-understand. Apple’s sample scripts provide good examples to work from.

Finally, the programmers Apple contracted to write Disk Copy 6.x maintain a Web page with some useful DiskScripts and AppleScripts at:

At about $10 (shareware) each the scripts are a bit expensive, but they appear to be of high quality.

A Few More Comments

Although in the past Disk Copy has been extremely reliable and stable, I have encountered a few problems with the newest version, 6.3. For instance, Disk Copy sometimes fails when creating a disk image if data extends all the way to the end of the source disk. A workaround is to make the image slightly larger than the required size.

In my experience, Disk Copy 6.2 is much more stable and encounters far fewer errors than version 6.3. If you can find a copy of it, I recommend using it. (Version 6.2 also includes a funky Appearance Manager incompliant progress bar that shows how much space is being saved by compression.) If you do decide to use version 6.3 contains some information about a known bug and its workaround.

That’s it. As you can see, I think disk images are amazingly useful creatures. Even if you have no use for floppy disks, there are plenty of ways disk images can come in handy. Write me at if you come up with any cool uses for disk images that I haven’ t mentioned.

[apple graphic] “The Personal Computing Paradigm” is copyright © 1998 by Michael Tsai,

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Reader Comments (4)

Nasir Sobri · December 16, 2000 - 01:01 EST #1
Turning disk images into floppies might not be a good idea, but how about turning them into CDs, a sufficiently fast medium.

I was wondering if we can burn (convert) a DiskCopy/ShrinkWrap img into a CD? Do we need to first convert it into iso/cif format? Can PC CD- recorder be used to burn these .img files?

Michael Tsai (ATPM Staff) · December 16, 2000 - 01:01 EST #2
Yes, it's easy to convert an image to a CD. Just mount it with DiskCopy or ShrinkWrap and drag it onto Toast's window. Toast will treat it like an ordinary Mac volume. If your PC CD recorder works with Toast, then it will work with .img files.
anonymous · October 12, 2002 - 07:27 EST #3
How do I get this Disk Copy manual? Is it at I could not find it there.
train taruona · July 21, 2006 - 05:50 EST #4
Any of you guys can tell me what echoplexing is?

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