[Coco] Re: Disk Basic and 512 byte block floppies.

[Amardeep S Chana]

"Neil Morrison" <neilsmorr at hotpop.com> wrote in
message news:03b301c3df13$7fefcae0$1dad74ce at bc.hsia.telus.net...
>
> Maybe, but there is a table in all versions of MSDOS which is a list
> of disk parameters and amongst those is the sector size. This CAN be
> altered by software enabling you to read/write/format all sorts of
> strange formats, including single density on the very few machines
> whose hardware supports that.
>
> See AnaDisk as an example of a program that does just that.
>
> NM

There is a BIOS Parameter Block and a related MS-DOS structure called a
Drive Parameter Block.  Both structures have an element called "number of
bytes per sector".  It is a 16-bit integer used for capacity calculations at
the file system level.  Changing this value does not instruct the default
driver to alter its sector_size parameter passed to the disk controller.  It
only alters the apparent size of a volume calculated by a routine calling
int 21h function 32h and related service functions.

Anadisk uses neither the BIOS nor DOS for disk I/O.  It acts directly on the
FDC register set.  One reason is the lack of support for density select in
the BIOS/MS-DOS drivers but there are numerous others.

Amardeep