Path: utzoo!attcan!sobmips!uunet!samsung!usc!rutgers!aramis.rutgers.edu!porthos.rutgers.edu!csirmaz From: csirmaz@porthos.rutgers.edu (Laszlo Csirmaz) Newsgroups: comp.sys.ibm.pc Subject: Re: I think I found how to write 360K on AT 1.2M drives Message-ID: Date: 15 Nov 89 19:56:21 GMT References: <859@cybaswan.UUCP> Organization: Rutgers Univ., New Brunswick, N.J. Lines: 39 Maybe all of this staff I want to explain is known for everybody in the netland, so I apologize advance.... The difference between the 360k and 1.2M floppy drive is twofold. First, the 1.2M drive has twice as many track as the 360k drive does (80 tracks versus 40). Second, each track on an 1.2M floppy contains more sectors than on the 360k floppy (15 versus 9). Thus writing a 360k floppy on a 1.2M drive, the drive has to do the following: use low density and use every other track only. The first of them is built in property of the drive: either it can do it or it can't. The second is a property of the software (presumably the BIOS) so it can automatically double the track number. The BIOS decides what kind of floppy it is dealing with in the following way. If the floppy is changed then it reads in the first sector on track 0 -- first with high density, and if unsuccesfull then with low density. In the first case the floppy is regarded as a 1.2M, in the second as a 360k. Each subsequent transaction to the drive is done according to this original decision, until the floppy is not changed. A nice exception is the "format" routine. It may, or may not inform the BIOS about the newly formatted floppy. Thus after formatting a floppy with the /4 parameter (if that works) it may be useful to take the floppy out and insert again, asking for a "dir". But anyway, the BIOS has the right to do what it wants, this is only ONE of the possibilities. If it does differently, then..... The head of a 1.2M floppy drive is about half as narrow as that of a 360k driver. This means that the 1.2M driver can modify smaller region thus the floppy produced in this way may be unreadable by a traditional 360k driver! And vice versa. If a floppy was written by a 360k drive, then a 1.2M drive cannot overwrite every information on it. The gaps might be filled with strong magnetic flips, which may cause erroneous reading. This is the reason why certain "format" programs do not allow reformat to 1.2M a floppy which has been formatted (maybe mistakenly) to 360k. Hope this helps ... Laci