Regained DOS recognition of 80GB USB External Hard Disk Drive (EHDD)
Systems, USB Hardware/Drivers, EHDD as described in initial post.
Although I did know of the MSDOS 8GB partition limit, I blindly followed the OEM admonition against attempting to partition the 80GB drive. It initially seemed wise since I had drive access in both Win98 and in real mode DOS. Currently I do not know why real DOS access initially succeeded! I now understand why the OEM presumed DOS access was not possible (at least they did not want to bother with support) and warned owners not to partition the drive. But hey DOS backup against internal HD failure (when you have more than one machine) is one of the main reason you buy one of these EHDD!
Set about to size some partitions at 8GB and immediately encountered the Catch-22 that all partitioning instructions and most software presume operating in real DOS mode. But I could not access the drive from real DOS because the ASPI-LogicalDrive mapper (DI1000DD.SYS or ASPIDISK.SYS) hung if it saw any partition above 8GB in its CHS-LBA calculations.
(... snip many hours of experimentation, searching and anguish ...)
SOLUTION:
1. Initially use FDISK and FORMAT from within protected DOS mode which is OK when working on a drive that is not the active OS. FDISK suffers from the MS imposed limitations of creating only DOS partitions and allowing only one primary DOS and one extended partition per table. FORMAT in protected DOS mode seems to get an initial primary DOS partition 8GB or less OK, but when doing subsequent partitions on the large drive it got the sizing all wrong. My guess is that protected DOS mode works through the virtual Win drivers and not directly with the BIOS LBA int 13h and therefore gets confused on the CHS-LBA translations.
2. Use PTEDIT32.EXE (much more useful than FDISK) to create up to three 8GB primary DOS partitions Type = 0Ch and hide the fourth partition entry from DOS (e.g. Type = 1Ch). Actually you could make this fourth partition extended and continue to create DOS logical drives up to 8GB. If the final partition exceeds the 8GB limit it must be hidden from DOS (and therefore from Windows too - but you can use this remaining space to experiment with other OS).
3. Once the ASPI-LogicalDrive mapper see only drives of 8GB or less it is happy and mounts the drives. Use FORMAT.EXE from within real DOS to make the drives accessible for read/write.
NB: If you use PTEDIT32.EXE, there is a nice help file by Dan Goodell at http://www.goodells.net/multiboot/ Be careful to note the 1023 cylinder limit (important so the editor doesn't choke but unimportant in LBA) and the start head cylinder 1 for the initial partition entry in any table due to the 63 hidden sectors.
Thanks to the above respondents.
