Hi all, just saw those clarifications from Jack in another thread: > Re: the 16-Jul-2005 comments by Eric Auer on FD-Devel (in reply to the > man that wants larger disk partitions), be advised that UDMA2 does not > process ONLY the following I-O requests:
[while it is busy, because it is not reentrant / if sector count is 0 or above 128 / if buffer address is -1, meaning 64-bit] > ALL other I-O requests WILL be handled by UDMA2, UNLESS the driver IS > NOT using its XMS memory buffer. If the system was loaded without an > XMS manager (HIMEM, FDXMS, etc.), or if UDMA2 was loaded with its /B > switch, ONLY THEN will UDMA2 pass misaligned or boundary-crossing I-O > requests to the BIOS... [...and XDMA is like UDMA2 but XDMA even insists on using an XMS buffer. However, it has some sanity checks removed and will e.g. crash on pre-386] Well, I had forgotten that the DEFAULT for UDMA2 is to use the XMS buffer. So this means that it would be SAFE to introduce a SYS CONFIG option "ignore reported disk size: assume 1024 cylinders in CHS mode and 2^32 sectors in LBA mode" - as long as it is made clear that this option must only be switched on by users who - in CHS mode, have a BIOS setup which reports the wrong cylinder count but the right sectors-per-track and head count - in LBA mode, WILL load UDMA2 (or XDMA) and WILL load HIMEM and WILL NOT use the UDMA2 /B option, and WILL NOT access drives which are beyond the BIOS-reachable region (e.g. first 8, 32 or 128 GB) until they have loaded HIMEM and UDMA2. Of course this option must not be used by stupid users, but I would be very happy to let FreeDOS bypass the 32 or 128 GB limit of some BIOSes simply by loading UDMA2 (which rocks :-)). This option can come either in RAW style: - only allow a partition to cross the declared end-of-disk of the BIOS or in ADVANCED style: - continue to read the partition table to find partitions beyond the originally reachable range as soon as the reported LBA disk size grows (i.e. after UDMA2 is loaded), to find more drive letters For CHS-only BIOSes, there will only be ONE style: - just ignore the BIOS-reported cylinder count and keep going :-) I hope that was convincing enough for Jeremy 8-). Eric ------------------------------------------------------- SF.Net email is sponsored by: Discover Easy Linux Migration Strategies from IBM. Find simple to follow Roadmaps, straightforward articles, informative Webcasts and more! Get everything you need to get up to speed, fast. http://ads.osdn.com/?ad_id=7477&alloc_id=16492&op=click _______________________________________________ Freedos-devel mailing list Freedos-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freedos-devel
