Most OEMs define a megabyte as 1,000,000 bytes, while the Macintosh considers a megabyte to be 1,048,576 bytes (1024*1024 bytes). The result is that the formatted capacity as reported by the Mac is about 4 1/2 percent less than the OEM's rated capacity. Some resellers (such as APS) should be commended for advertising formatted capacities.

When using an external hard drive, the drive must always be turned on before the computer. A ridiculous, though common ailment is a loose SCSI cable. Listen for the drive to make sounds -- on an external enclosure you will typically hear both a cooling fan and the drive itself. External drive enclosures come in a variety of qualities. Keep this in mind as you determine if the whole drive is shot or if just the enclosure needs replacing. See SCSI troubleshooting for more info on SCSI devices.

You can buy a case for it, though the cost may be prohibitively expensive for small drives. You can sometimes find used cases for thirty to fifty dollars, though you'll have to do some searching.

You may want to put the old drive in a drawer for safekeeping. When you sell the computer, you can sell it with the smaller drive, and move the larger drive to your new computer.

If you have an empty drive bay, you can mount the drive internally with a twenty dollar bracket kit. Your local Apple dealer can probably get the bracket you need. This is ideal if you have an empty CD-ROM bay.

Finally, you can simply sell the leftover drive, but you probably knew that already.

Assuming you had a working hard drive the last time you used your Mac (and assuming you have used it at all in the last few years), you have experienced a hard drive crash. Donžt panic too much yet. There are two kinds of hard drive crashes: the data crash and the hardware crash. Listen for your hard drive when you start the machine. If you hear it spinning (a ticking sound that is not the hum of the fan), then you may still be in business. Slip in your emergency floppy that came with the machine and go to work. Chances are your hard drive has misplaced enough of your operating system that your Mac can't start up.

If there is no sound from the hard drive, it's just not spinning up, bring the machine in to an Apple Authorized Service Center or call your clone manufacturer for service. Good thing you had a backup copy!

The obvious way is to have your hard drive replaced with a larger one. This is not always the best thing to do though. A less permanent, and more flexible way is to buy either an external hard drive or a removable cartridge drive. Either would connect externally to the SCSI port (see SCSI in troubleshooting) and avoid the costs of installation and formatting an internal drive.

Simple, just restore your backup copy! What? No backup copy? OK. There's still a slight chance you might be able to recover your lost data. The most feasable way is to purchase a utility program that specializes in maintaining your hard drive. These programs will warn you that installing the program after you have experienced a loss of data might permanently erase the data by installing over it. If this doesn't happen, the chances are still pretty slim that a recovery can happen. If you use the program right, you will be covered the next time you lose data.

Your other option is a hard drive recovery service. This is very expensive, and still might not be able to reconstruct corrupted data.

How do I put my old internal hard disk in an external case?

Alliance Peripheral Systems, 800-443-4199/816-483-6100 sells cases for old internal 3.5 inch drives for $179.95 plus shipping and handling (about ten to fourteen dollars). The price includes instructions and technical support for the installation.

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How do I put my old internal hard disk in an external case?

Alliance Peripheral Systems, 800-443-4199 or 816-483-6100 sells cases for old internal 3.5 inch drives for $179.95 plus shipping and handling (about ten to fourteen dollars). The price includes instructions and technical support for the installation.

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Should I get an internal or external hard drive?

The main advantage of buying a replacement internal drive is that it's cheaper than an external drive: typically seventy to a hundred dollars cheaper.

An external drive has many advantages. You can easily move your data from the old drive to the new drive, and there's no installation involved. You'll also have a second drive, which is handy for transportation, backing up, reformatting, etc.

If you chose to buy an external drive that's larger than your internal drive, you can move the larger drive inside your computer, and move the smaller drive to the external case. This does require some mucking around inside your computer. In particular, you'll probably need to change the SCSI ID and the termination. If you're not comfortable making these modifications, have a friend or a technician do them for you.

Much of the information contained herein has been extracted from Elliotte M. Harold's incredible FAQ lists. We thank and commend him for his invaluable service to the Macintosh world.