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-inch 1.44 MB FDD can read, write, and format 720 KB (DD) and 1.44 MB (HD) diskettes. 3.5-inch 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-inch 1.2 MB FDD can read any 5.25-inch 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 drive 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 10 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.
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-inch 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-inch 1.44 MB FDD in nearly any 286 or later computers 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-inch 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-inch drive. If that occurs, your only alternative is to locate an actual 5.25-inch 360 KB drive and use it to do the transfer.