Universal drive Part 1: The DRIVE

[The fundamental components would be the disk drive (either stock or modified), the controller (possibly heavily modified), and the software] Hard versus soft sectoring, FM / MFM (single/double denbsity) / GCR are primarily an issue of controller, although drive hardware can play a part. For example, Apple ][ used different circuitry on the drive (that was otherwise basically a Shugart SA400); BUT, Apple ][ diskettes CAN be read with most "normal" 360K drives using special controllers. Directory structures (CP/M, TRS-DOS, etc.) are almost entirely a software issue. Although hardware issues must be resolved first, and controller can be an issue [how many remember the Data Address Mark issues with double density on TRS-DOS and derivatives?] The common sizes of disk drives are: 8" 5.25" 3.5" There have also been a few others, including: 3" (Amstrad, Canon, earliest Gavilans,Amdek add-on for Aplle and Coco) 3.25" (Dysan bet the copany and lost. Seequa Chameleon 325) 3.9" (IBM. never produced??) 2.5" (Zenith?) On 5.25" drives, there were a few different intertrack spacings, most common being 48TPI (tracks per inch) 96TPI (""Quad"" density, and 1.2M "high" density) There was also a short-lived 100TPI (Micropolis series 2 and Tandon TM100-4M (M designating 100TPI v the more common 96TPI of 100-4)) Anybody remember the AMLYN drive? capable of variable track spacing, and had a crude jukebox for swapping 600 Oerstedt (1.2M) diskettes. 3.5" drives are normally 135 TPI, although there were some early 40 track (Epson Geneva) at 67.5 TPI 8" drives normally ran at 360 RPM. 5.25" drives normally ran at 300 RPM, except for 1.2M, which thought that it was an 8". That doesn't REALLY matter, since it can be compensated for by changing the data transfer rate at the controller. -- Fred Cisin cisin(a)xenosoft.com XenoSoft http://www.xenosoft.com 2210 Sixth St. (510) 644-9366 Berkeley, CA 94710-2219