A removable disk or cartridge lets you create a backup of your data, which you can carry with you or store at a safe location. If your drive fails, you can still get to your documents by using the removable disks with another machine. Also, if you have a copy of your system on a removable disk, you can use this to start up your computer in an emergency.
Most disks are in one of two broad categories; optical and magnetic, as described below.
Generally speaking, optical disks are economical and reliable for the long-term storage of data, with an inherent immunity to magnetic fields. Variations on the standard optical formats of CD and DVD can also be used in all modern computers.
In comparison, blank magnetic disks are expensive. Older formats, as devised by SyQuest, Bernoulli, or Ricoh, use reliable Winchester technology, as in a fixed drive. However, newer techniques have emerged, all using a higher recording density on a non-rigid disk that rotates at a much slower speed. Unfortunately, these later formats aren’t always trustworthy.
Desktop computers usually have a spare drive slot that can accept a removable disk drive mechanism. This gives easy access, doesn’t occupy any space and uses the Serial ATA, ATA/EIDE or SCSI connections in the slot. Even so, you must check that the drive is suitable for your computer and that the latter supports the number of drives that you require.
Failing the above, you can connect an external drive to a spare port on your computer, preferably of the FireWire variety. The USB 2.0 ports on a modern machine are sufficient for a modest drive, especially without other devices connected, but the USB 1.0 connections on an older machine are too slow, despite being adequate for a floppy disk drive.
A removable disk should auto-mount when inserted, which requires appropriate driver software to be resident in RAM. This consists of one or more special files, as supplied with the drive, which are loaded into memory at startup.
Although folders and files can be copied to a backup disk by dragging them in the Finder, it’s often easier to use an application such as Retrospect or Synchronize! to provide an automated backup process.
If you want to make an exact ‘bit-for-bit’ copy of a removable disk you can use Disk Utility, a useful application supplied with Mac OS X 10.3 or higher. First, you must create a disk image file of the original disk and then you can copy the contents of this image to the destination disk. To make the image, choose Images ➡ New ➡ Image from disk and select the source disk. At this stage you can choose the disk size, format and whether or not you wish to use encryption.
Having made the image, you can select Images ➡ Burn to burn the information onto a CD or DVD. To copy the contents to a destination volume, select the Restore tab, highlight the required disk image and select Images ➡ Scan Image for Restore. Then you can drag the image to the Source field, the destination drive to the Destination field and click on Restore.
Apple’s older Disk Copy application is easier to use than Disk Utility, allowing you to copy disks of the same size. It can also store a disk image on your hard disk, which you can mount as a normal removable disk: and you can drag files in and out of it.
Finding out how many files will fit onto a removable disk can be tricky. Here’s one way of doing it:-
Software is often protect from illicit copying by means of passwords or registration numbers. In some instances, the associated registration, authentication or activation process is done online or via a telephone service. Unfortunately, some types of activation only allow you to use the application on the machine onto which it was originally installed.
The most effective protection systems for the Classic Mac OS are based on modifications to the low-level information on those parts of a floppy disk only normally used by the system or its disk drivers. This causes read errors when a disk copying program is employed. A key disk is similar, except that the actual software isn’t stored on the disk itself. Instead, you have to insert the disk to start an installation or each time you launch the application after starting the computer.
Some packages employ an installer application that allows you to make a given number of copies of the required software from the installation diskette to your drive. You may be able to uninstall some copies but the installer remembers the location of each copy. If you try to make further installations you’ll be thwarted. Some people make copies of the original disk as a disk image (see above), acting as a safety backup, although this trick can also be used to create illicit copies.
©Ray White 2004.