6.6 Working with Obsolete Diskette Formats

If you've been computing for a long time, it's sometimes necessary to read a diskette written in an obsolete format. You may also need to format and write a diskette in an obsolete format, e.g., to create a boot diskette for an older system whose hard drive will not boot but still contains valuable data. If you find yourself in such a position, keep the following issues in mind:

• A 3.5" 1.44 MB FDD can read, write, and format 720 KB (DD) and 1.44 MB (HD) diskettes. 3.5" 2.88 MB (ED) diskettes are readable only by an ED drive. These are difficult to find new, so your only option may be to locate someone with an ED drive who is willing to allow you to use it to transfer your data.

• A 5.25" 1.2 MB FDD can read any 5.25" diskette written with an IBM format in any 360 KB or 1.2 MB drive. A problem may arise when you exchange 360 KB diskettes between 360 KB and 1.2 MB drives. 360 KB drives write a wider track than 1.2 MB drives, which cannot completely erase or format data put down by 360 KB drives. If a 360 KB drive formats or writes to a 360 KB diskette, a 1.2 MB can subsequently read, write, or format that diskette, but once that diskette has been written or formatted in the 1.2 MB drive, it will no longer be reliably readable in a 360 KB drive. This problem does not arise if the 360 KB diskette has never been written to in a 360 KB drive. Accordingly, if you need to write data with a 1.2 MB drive that must subsequently be read by a 360 KB drive, use blank 360 KB diskettes (bulk-erased, if necessary), and format them to 360 KB in the 1.2 MB drive.

• Old diskettes often have errors, either because the diskette has been physically abused or simply because the magnetic domains on the diskette have gradually faded with time. Reading data from a diskette that was last written five or more years ago is very likely to yield some read errors; a diskette ten or more years old is almost certain to have multiple read errors, and may be completely unreadable. Using the diskette rescue utilities included with Norton Utilities for DOS (http://www.symantec.com) and SpinRite (http://www.spinrite.com) can often retrieve some or all of the data from a marginal diskette.

  If the data is critical, consider sending the diskette to one of the firms that specialize in data retrieval and advertise in the back of computer magazines. These services are not cheap, and cannot guarantee that the data can be salvaged, but they do offer the best hope. If the data is important enough to pay a data retrieval firm to salvage, send the diskette to them without trying to salvage the data yourself first. Running one of the utilities mentioned previously may render what would have been salvageable data unreadable by the data retrieval company.

• You can generally install a newer FDD in an older system and use it to emulate an older FDD, with the following limitations:

  • The 5.25" 1.2 MB FDD spins at 360 RPM (versus 300 RPM for all other FDDs) and cannot be used in a system whose FDD controller supports only 360 KB FDDs.

  • You can install a 3.5" 1.44 MB FDD in nearly any 286 or later computer and some late-model XT clones, although the drive may be recognized only as 720 KB. If that occurs, use 720 KB (DD) diskettes in that drive. In theory, you should also be able to install a 3.5" FDD in a PC or XT-class system and use it as a 360 KB FDD. In practice, this works on some PC and XT-class systems, but not all. For reasons that are not clear to us, some old systems refuse to recognize the 3.5" drive at all. If that occurs, your only alternative is to locate an actual 5.25" 360 KB drive and use it to do the transfer.

To use this method, you also have to temporarily reconfigure the 3.5" drive on the modern system to 360 KB in order to read and write 360 KB 3.5" diskettes. Some systems allow this, but others return a hardware error. Before you install the 3.5" FDD in the older system, check the newer system to make sure that it allow its 3.5" drive to run as a 360 KB 5.25" drive. To do so, run BIOS Setup on the newer machine, set the drive type to 360 KB 5.25", and restart the system. If the system does not return a hardware error, insert a blank 720 KB (DD) diskette into the drive and issue the command format a:. If the diskette formats successfully to 360 KB, that drive is usable for your purposes.