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Mail Archives: opendos/1998/04/14/07:01:03

Date: Tue, 14 Apr 1998 12:27:32 +0100
From: Matthias Paul <PAUL-MA AT reze-1 DOT rz DOT rwth-aachen DOT de>
Subject: Re: Harddisk Question
To: opendos AT delorie DOT com
Reply-to: Matthias DOT Paul AT post DOT rwth-aachen DOT de
Message-id: <223ADE13C21@reze-1.rz.rwth-aachen.de>
Organization: Rechenzentrum RWTH Aachen

On Sun, 12 Apr 1998 Paul fULLER asked:

> G'day, whats the biggest hard disk that you can run unpartioned with
> OpenDOS compared to MS-DOS ? Is it 4.3 gig for both?...
The maximum partition size for FAT16 is about 2 GB for both DOSes 
(because of the 32 KB cluster limitation in MS-DOS).

(Maybe, DR-DOS would support 64 KB clusters for up to ca. 4 GB FAT16
partitions, but DOS FDISK does not allow to create such partitions. 
NT FDISK does, but I've nevr tried what happens if you try to use 
DR-DOS on such a partition. Doesn't make much sense anyway...)

However, the maximum partition size of a DOS drive also depends on
your ROM-BIOS support, and peculiarities in INT 13h implementations. 
(Without special drivers) old ROM-BIOSes do not support hard disks 
beyond about 530 MB, but this limitation is not imposed by DOS. Some 
ROM-BIOSe also have problems to access hard disks beyond about 1 Gb 
(some old SCSI BIOSes), 2,?? Gb, and 4,?? Gb. These limitations are
due to the C/H/S remapping (physical & logical geometry), different 
access methods (logical C/H/S or LBA), and some unsupported 
combinations of C/H/S under MS-DOS, which BIOSes usually try to avoid
for reasons of compatibility. Only very new BIOSes (1997+) support
hard disk beyond 8 Gb (the physical limit of the traditional 
INT 13h interface) using so called 'INT 13h extensions' (which cannot
yet be used by any DOS - with the exception of Windows 95 OSR2+).

Matthias

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