Hi!
21-Окт-2004 17:09 [EMAIL PROTECTED] (Daniel Gustafsson) wrote to
<[EMAIL PROTECTED]>:
DG> 1. Does freeDOS have a ramdisk
Yes - it "have" (ie. there may be used) same ramdisks, as under MS-DOS.
AFAIR, into FreeDOS distribution included one of them - TDSK.
DG> and if so how do I use it?
Same, as under MS-DOS.
DG> 2. What does execrh do?
Comment from execrh.asm: "request handler for calling device drivers".
Although DOS isn't modular system, but it allows to load device drivers and
its own lowlevel functions accessed through common device drivers interface,
Thus, all IO requests are passed to device drivers (and kernel provides some
default drivers like CON:, C:, etc). execrh() performs device driver call
itself.
DG> 3. Bart wrote:The default block device driver is in dsk.c, dsk.c then
DG> translates relative (partition) sector numbers into absolute (disk)
DG> sector
DG> numbers and (unless using LBA) cylinder/head/sector, and calls int13 BIOS
DG> functions via floppy.asm.
DG> > "unless using LBA": explain please...
Very old machines (below 486) doesn't support disk larger than 504Mb.
This is because difference between IDE interface and BIOS API. This
limitation was solved by introducing translation, when BIOS emulates one
disk geometry, but inside uses "real" geometry (which is informed by disk
itself). This allows to access through standard BIOSes up to 8064 Mb disks.
But disks growth over this barrier, so there was introduced new BIOS API,
which allows to access disks not through cylinder/head/sector, but directly
through "absolute" sector number (so called Logical Block Addressing, when
all disk sectors commonly enumerated).
dsk.c translates LBA-sector number to CHS-numbers for drives, for which
BIOS doesn't support LBA access, and uses LBA-sector number directly in
other cases.
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