Mail Archives: opendos/1997/12/10/14:32:54
On 97/12/10 Ben Jemmett replied:
>>I recently installed a 3 1/2 disk drive on it. 720K disks work fine, but I get
>>a "sector not found" error or "general error" when trying to use 1.44 MB
>>disks.
>Old, old, old 8088 - XT or previous, I assume. XTs and previous models
>can't handle drives above 720K - the data seperator on the FDD controller
>can't handle the data rates from 1.44 and 1.2 Mb drives - [...]
This is correct, if speaking of the original XT-FDC controller. But many
XTs today use FDCs on Multi-IO cards which usually support up to
2 drives á 1.44MB (some even support 4 drives á 1,44MB). They also
have a ROM/EPROM which replaces the ROM-BIOS floppy code, so
that these XTs are fully capable of 1,4MB drives.
>Don't know about the switch, but the drive is not handled by the BIOS, so a
>BIOS patch won't make your system compatible with high density drives.
Not alone. To support 1,4MB drives (on any machine), it needs
- a correctly jumpered 1,4MB drive
(I assume this as given)
- a FDC capable of the high density data rates
(in my former reply I also assumed this as a given requirement)
- a software driver, which usually resides inside of the ROM-BIOS,
or in the case of AddOn FDCs, inside of an external ROM/EPROM.
I refer to these ROM-based drivers in Digitial Research s terminology
as ROS (ROM Operating System).
(A software only driver like 2M s 2M-XBIOS is also possible without
the need of a special ROM. It is just loaded by IBMBIO.COM)
The (Real Mode) DOS kernel consists of two parts, the DOS portion of
the "BIOS" (inside of IBMBIO.COM, that s why I usually call the ROM-based
BIOS "ROS", not BIOS) and the "BDOS" (inside of IBMDOS.COM). In short
words, the high level (and portable) DOS functions (in BDOS) are based on
more-hardware-dependent drivers in the BIOS, which themselfs refer to the
very-hardware-dependent ROS (which can be overlayed by an installable
driver). Well, the terminology differs between authors, some call ROS+BIOS
the BIOS... (which is also true).
Anyway, given the proper hardware, it is possible to support 1,4MB floppies
in PCs and XTs by a ROS update, or a software driver. Of course, the
later solution cannot be used to boot from 1,4MB floppies, whereas this
is obviously no problem for a ROS-based driver.
Matthias
------------------------------------------------------------
Matthias Paul
eMail: <Matthias DOT Paul AT post DOT rwth-aachen DOT de>
Web: http://www.rhrz.uni-bonn.de/~uzs180/mpdokeng.html
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