Re: [Freedos-user] Large hard disk (> 1024 cylinder) support?

[Eric A. <er...@co...>]

Hi Frank,

> I'm thinking of installing FreeDOS on my hard disk, but as my free partition
> is beyond the 1024-cylinder mark, I'd like to know the status of FreeDOS's
> support for large hard disks. Does the current version of FreeDOS have
> built-in support for accessing partitions beyond the first 1024 cylinders?

Yes, no problem at all. The limit is how much your BIOS can
handle. BIOS limits can be: 512 MB, 2 GB, 8 GB, 32 GB, 128 GB.
With a modern BIOS with LBA48 support, you can use even more
than the first 128 GB: In that case, the limit is that normal
partitions can only be in the first 2 Terabyte of your disk ;-).


> Can I boot FreeDOS from such a partition? Are there any FreeDOS
> programs which may have problems with such partitions? Thanks!

Yes, but you may have problems with FAT32, as our SYS tool
sometimes thinks that you mean FAT32-CHS instead of FAT32-LBA,
and only FAT32-LBA can boot outside the first 1024 cylinders.
As a workaround, you can use FAT16, or use my Perl script
"FreeDOS SYS for Linux" ;-). Our normal SYS always supports
LBA for FAT16, so there is no 1024 cylinder limit in FAT16.

Only very few FreeDOS programs access the harddisk directly,
most programs ask the kernel to do that for them. Because our
kernel supports up to 2 Terabyte disk size, you should not
notice anything special when using FreeDOS on big harddisks.


Exceptions: Our disk cache accesses the harddisk directly,
but it supports up to 2 Terabyte disk size, too. Same for
the UDMA driver for DOS :-). The DOSFSCK tool (similar to
CHKDSK and SCANDISK, but supports FAT32 and some extra
features) might need 100s of megabytes of RAM if you try
to "checkdisk" a very large FAT32 partition with it. The
DEFRAG tool will probably take ages to defrag such a drive.

So in general: You may get bad performance when you try
to use DOS on really big _partitions_, but you should not
be experiencing any problems with big harddisks as long
as they contain only small DOS _partitions_ of up to a
few gigabytes size.

Enjoy DOS and let us know if you notice problems :-).

Eric

PS: for some known issues, see the install wiki page -->
fd-doc.sourceforge.net/wiki/index.php?n=FdDocEn.FdInstall