jpw@cblpf.ATT.COM (Mike Vehonsky) (08/20/87)
If a hard disk has been formatted with DOS version "X", what determines whether or not you will be able to read it when you boot DOS version "Y" from floppy. We just loaded 3.2 on our system (PC6300, 10 Meg). If you boot version 2.11 or 3.1 from floppy, and try to access the C: drive, you get an "Invalid drive specification". I think that it may have to do with cluster size, but the strange thing is that another machine (also running 3.2) CAN be booted with a different version and read the hard drive just fine. Any insight would be appreciated. Mike Vehonsky AT&T Network Systems ihnp4!cblpf!jpw
gmv@cblpf.ATT.COM (G. Michael Vrbanac) (08/20/87)
> If a hard disk has been formatted with DOS version "X", > what determines whether or not you will be able to read > it when you boot DOS version "Y" from floppy. > > We just loaded 3.2 on our system (PC6300, 10 Meg). If > you boot version 2.11 or 3.1 from floppy, and try to > access the C: drive, you get an "Invalid drive specification". > I think that it may have to do with cluster size, but the strange > thing is that another machine (also running 3.2) CAN be > booted with a different version and read the hard drive just > fine. Any insight would be appreciated. > > Mike Vehonsky > ihnp4!cblpf!jpw To draw an analogy to the UNIX world, the DOS format really doesn't "format" but rather makes a file system. (a PC "low-level" format is equivalent to a UNIX "format"). The DOS "file-system" changed with version 3, and is downward compatible with DOS 2.xx but not upward compatible with DOS 2.xx. Thus a machine booted with 3.2 can read 2.xx disks, but a 2.xx DOS can't read 3.2 formatted disks. Note this is the 12-bit versus 16-bit FAT (file-allocation-table) change. +---------------------------------------------------------+ | Mike Vrbanac AT&T Bell Laboratories Columbus, Ahiya | | Unix: {cbosgd|ihnp4}!cblpf!gmv CompuServ: 76054,113 | +---------------------------------------------------------+
psfales@ihlpe.ATT.COM (Pete Fales) (08/21/87)
In article <680@cblpf.ATT.COM>, jpw@cblpf.ATT.COM (Mike Vehonsky) writes: > > If a hard disk has been formatted with DOS version "X", > what determines whether or not you will be able to read > it when you boot DOS version "Y" from floppy. > > We just loaded 3.2 on our system (PC6300, 10 Meg). If > you boot version 2.11 or 3.1 from floppy, and try to > access the C: drive, you get an "Invalid drive specification". > I think that it may have to do with cluster size, but the strange > thing is that another machine (also running 3.2) CAN be > booted with a different version and read the hard drive just > fine. Any insight would be appreciated. I am not positive, but I'll take some guesses: Guess #1: It is a well known fact that Microsoft introduced the 16 bit FAT (i.e. smaller hard disk cluster size) in version 3.1 (or 3.0??), but AT&T did not introduce it until 3.2. This means that once the disk has been formatted with anyone's 3.2, it can be read by anyone's 3.2 but only by the Microsoft version of 3.1. Guess #2 (more likely as I think about it): If the disk on your second system was formatted with pre-3.2 and then 3.2 installed without reformatting, it will retain the larger cluster size. Thus, it can be read by any version of DOS. -- Peter Fales UUCP: ...ihnp4!ihlpe!psfales work: (312) 979-7784 AT&T Information Systems, IW 1Z-243 1100 E. Warrenville Rd., IL 60566
bw@hpcvlo.HP.COM (Bill Wilhelmi) (08/21/87)
Don't boot 2.11 and try to write to your hard disk formatted with 3.x. DOS 2.x formats hard discs using a 12-bit File allocation table. DOS 3.x formats hard discs using 16-bit File Allocation Table entries. If you write to a hard disc formatted with 16-bit FAT entries using an operating system that thinks its dealing with 12-bit FAT entries, you can kiss the data on your hard disc goodbye. Bill Wilhelmi Hewlett-Packard Corvallis, Oregon
tla@kaiser.UUCP (T Anderson) (08/22/87)
>> If a hard disk has been formatted with DOS version "X", >> what determines whether or not you will be able to read >> it when you boot DOS version "Y" from floppy. >> >> We just loaded 3.2 on our system (PC6300, 10 Meg). If >> you boot version 2.11 or 3.1 from floppy, and try to >> access the C: drive, you get an "Invalid drive specification". >> I think that it may have to do with cluster size, but the strange >> thing is that another machine (also running 3.2) CAN be >> booted with a different version and read the hard drive just >> fine. Any insight would be appreciated. >> >> Mike Vehonsky >> ihnp4!cblpf!jpw > To draw an analogy to the UNIX world, the DOS format really doesn't > "format" but rather makes a file system. (a PC "low-level" format is > equivalent to a UNIX "format"). The DOS "file-system" changed with > version 3, and is downward compatible with DOS 2.xx but not upward > compatible with DOS 2.xx. Thus a machine booted with 3.2 can read > 2.xx disks, but a 2.xx DOS can't read 3.2 formatted disks. > Note this is the 12-bit versus 16-bit FAT (file-allocation-table) change. Actually as the original author observed it is not as bad as the above. The only problem is DOS x with x<3.0 (or in AT&Ts case x<3.2) ONLY 12 bit FAT was supported so if using a later DOS the disk was formatted with 16 bit FATs then they can no longer be read by the earlier DOSs. But even the newer DOSs (by default) only uses the 16-bit FAT for disks larger than 10M. So even with the newer DOS 10M and smaller disks use 12 bit FATs and CAN be read by earlier DOSs. Disks larger than 10 M formated by earlier DOS use 12-bit FATs and it is even possible with the more recent DOSs to force the use of the 12-bit FATs, which can then be read by all. Of course the disadvantage (and one of the reasons for introducing the 16-bit FAT) was that on a 20M disk with 12-bit FATs the cluster size is 8k. The 16-bit FAT reduces that to 2k. -- Terry L Anderson AT&T Bell Laboratories -- Liberty Corners UUCP: ...!ihnp4!kaiser!tla TeleMail: Terry.Anderson (201) 580-4428
dave@westmark.UUCP (Dave Levenson) (08/23/87)
In article <680@cblpf.ATT.COM>, jpw@cblpf.ATT.COM (Mike Vehonsky) writes: > We just loaded 3.2 on our system (PC6300, 10 Meg). If > you boot version 2.11 or 3.1 from floppy, and try to > access the C: drive, you get an "Invalid drive specification". > ...another machine (also running 3.2) CAN be > booted with a different version and read the hard drive just > fine. You just loaded MS-DOS version 3.2 on your system. You probably re-formatted your hard disk in the process. This is useful, because it allows you to use the smaller cluster size, but it is optional. If you had an earlier version of MS-DOS, the 3.2 installation process allows you to skip the re-formatting step and just replace the system files. This is probably what was done with "another machine" whose hard disk is still accessible under older DOS versions. -- Dave Levenson Westmark, Inc. Warren, NJ USA {rutgers | clyde | mtune | ihnp4}!westmark!dave