This is "in-reply to" Czerno/Bertho: ... >>> Do you mean to say "non-IBM" ? UIAM again, the "IBM" (should be >>> called "MS") formats are the usual FAT disks. IOW "non-IBM" is when >>> attribute bit 13 =3D 1.
>> No, it's the other way around. If bit 13 is set, it means "IBM Format", >> but that doesn't equate to "MS". Here's a quote from an old book I >> have, "DOS Programmer's Reference", 2nd Edition, by Que, which gives >> the practical explanation of what the bit means, specifically regarding >> function 2, "Build BPB": > "A one sector buffer is passed to this routine. > If the non-IBM format bit in the device attribute word is set to zero, > the buffer contains the first sector of the FAT and should not be changed. > If the bit is set, the buffer can be used as a scratch area in which to > build the BPB." >> It doesn't have anything to do with non-FAT. > Oh, good to know. It' unclear still what these options were meant for... > Maybe a divergence of opinions between the teams at MS/big Blue ? > Bottom line for safety in the driver: ignore the setting of the bit, > assume you can't change the buffer, and assume the buffer does not > contain the first sector of the FAT. R.S. Lai "Writing MS-DOS Device Drivers" explains it a little more: - Early DOS versions recognized only a small number of disk types, through the "media type" byte, and had built-in tables with the BIOS parameters for these. - bit 13 set means the disk parameters do not correspond to any of the internal DOS tables. - While the buffer will still contain the first sector of the FAT if bit 13 is clear, DOS 3.3 and later does not look at it on return, so it can always be used as a scratch pad. IMO, the safe way is to have attribute bit 13 set and not use the buffer. The BPB shall be written to the address provided in function 02 "get BPB" request header. The buffer was never used to return it. JAS ------------------------------------------------------------------------------ Virtualization & Cloud Management Using Capacity Planning Cloud computing makes use of virtualization - but cloud computing also focuses on allowing computing to be delivered as a service. http://www.accelacomm.com/jaw/sfnl/114/51521223/ _______________________________________________ Freedos-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freedos-devel
