As distinct from diskette types and formats, six drive types have been installed in PC-compatible systems:
- 5.25” 160/180 KB (SSDD)
Single-Sided, Double-Density(SSDD) was the standard FDD in very early PC-class systems. These drives read and write only SSDD diskettes.
- 5.25” 320/360 KB (DSDD)
Double-Sided, Double-Density(DSDD) was the standard FDD in PC-class systems, and often found as a second FDD in early AT and 386 systems. These drives read and write single-sided (160/180 KB) and double-sided (320/360 KB) formats.
- 5.25” 1.2 MB (HD)
High-Density(HD)—this and all later formats are double-sided, but that part is no longer stated—is the standard FDD in 286, 386, and some early 486 systems, and often found as a second FDD in early systems with 3.5” primary FDDs. These drives read and write any 5.25” format. A diskette previously formatted or written to by a 5.25” DD drive and then written to by a 5.25” HD drive may not subsequently be reliably readable in any 5.25” DD drive.
- 3.5” 720 KB (DD)
Double-Density(DD) is an interim standard, commonly found as a primary drive in early low-end 286 systems, and as a secondary drive in a few PC-class systems and many 286, 386, and 486 systems. These drives read and write only the 720 KB DD format.
- 3.5” 1.44 MB (HD)
High-Density(HD) is the standard FDD on mainstream systems for the past decade. These drives read, write, and format any 3.5” HD or DD diskette.
- 3.5” 2.88 MB (ED)
Extra Density(ED) is a failed standard, ...