What problems do PC floppy disk controllers have with TRS-80 disk formats? What problems do different TRS-80 models have with each others disk formats?
The Western Digital 177x/179x floppy disk controllers that were used in TRS-80s have some capabilities that PC disk controllers generally lack. The executive summary is that (1) many standard PC floppy controllers can’t handle single density at all, (2) even those that can handle single density generally cannot read the directory track on a Model I TRSDOS disk, and (3) there can also be problems reading double density disks. Here are more details. Many PCs cannot handle single density (FM) encoding. The original Model I used single density exclusively, and even a Model I with a double density adaptor requires a single density boot sector on system disks. The original IBM PC controller required extra outboard components to support clock/data separation for single density, but IBM left them off to reduce their manufacturing costs. (So I’m told; I wasn’t involved with PCs in that era.) This started the tradition of leaving out single density support in PCs. Modern PCs use more highly inte
