OS/2 Professional/OS2PRO194.ISO/os2/diskutil/chkchg/chkchg.doc

Text File | 1993-09-06 | 1.9 KB | 32 lines

              CHKCHG Copyright (C) 1993 Dimitri Vulis [e-mail]

When OS/2 reads data (such as the root directory or the file allocation table)
from a diskette, and needs to refer to it again soon (e.g., to open another
file), it may not have to re-read it if the same diskette is still in the drive
and the data is still in the memory buffer. To determine whether the diskette
has been changed, OS/2 uses the hardware feature called "diskette change line".
Under normal circumstances, if the disk drive has been opened and closed and
therefore the diskette may have been changed, the diskette drive tells the OS
on a subsequent read that the diskette may have been changed, and the OS will
know the data in memory buffers cannot be reused and must be re-read.

Unfortunately, this mechanism does not work correctly on some clones. Sometimes
the drive fails to report that the diskette has been changed. With two
drives, sometimes a media change is reported on the wrong drive. Sometimes no
media change is reported when it fact there's no media in the drive and the
drive is not ready. This is also a malfunction, but it seems not to cause
problems for OS/2. OS/2 is also more sensitive than DOS to the drive
incorrectly identified in CMOS configuration (e.g., 1.2MB instead of 1.44MB).

If OS/2 assumes that a diskette has not been changed, when it fact it has, data
may be lost. For example, the root directory or the file allocation table of
the previously inserted diskette may be written into the new diskette.

The program CHKCHG will report the diskette change status returned to the
operating system by the diskette drive. You can open and close your drives and
see whether the program's output corresponds to what is happening in reality.

USAGE: enter chkchg at a DOS command line (any kind). It reports the current
status of your floppy drives. Open and close them and rerun to test.