Mail Archives: opendos/1997/12/12/11:39:57
>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.
I know- both my Amstrad PC's run these cards for drive B: - I didn't replace
A as my original 360K disks need the same drive to work properly, as they do
something nasty to the hardware (I think - all I know is it crashes on
boot-sector load if you have anything >360K on drive A:). However, it may
take a bit of fiddling to disable any on-board controller - on some
motherboards it's impossible. My Amstrads have their FDD controller on a
large, integrated chip of Amstrad's own design. I had to tell the machine
it had one drive (A:), then add the second controller for the second drive.
>
>>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)
Yes, I was just making sur everyone knew the cards had to be capable of high
data rates.
>- 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).
I though DR used ROS for the Resident Operating System. Sam thing, I
suppose, so no problems...
> (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)
You could also have a software-only driver loaded by the MBR or boot
sector - like Ontrack's Disk Manager for large HDDs.
>
>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.
Unless the floppies need the original drives for some reason - e.g. my disks
(see above). Very rare, I would assume.
Regards,
Ben Jemmett
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