26 Dec
2003
26 Dec
'03
3:51 a.m.
On Fri, 26 Dec 2003, Pete Turnbull wrote:
That is the same PHYSICAL format (apparently) as the TRS-80 model 1, and
the earliest Osborne computers (later, the Osborne went to double density,
with 5 1024 byte sectors)
servicebureay,
but according to the software BBC is found in quite
some
flavours, reaching from single-side
single-density 5.25" to DSDD 3.5"
Before you spend a lot of time playing around with things, it would
be good
to know the discs physicals and logicals.
The single-density "DFS" format is particularly easy. It consists of
10 sectors of 256 bytes per track, numbered 0 to 9, and is nominally
single-sided. If you have doubled-sided drives, side 0 of the first drive is referred to as drive 0, and the sector
headers are just as
you'd expect; the second side (side 1) is referred to as drive 2, and
has the *same* sector headers (ie the "head" number is stored in the
header as "0", not "1"). Drives can be either 40-track or 80-track;
Thus, to read the SECOND side, it will be necessary to talk directly to
the FDC, rather than using INT13h.
(Same thing applies to double sided Kaypro, and a number of others).
MANY computers that use INVALID head numbers in the sector headers ignore
the head number field except when formatting - for example, although
Kaypro puts head number '0' in the headers of the second side, it will
gladly read or write to a pseudo Kaypro disk that has the correct values
in the headers. (Format a disk with valid headers; write to it on the
alien machine; bring it back; and it is readable without "extra" effort)
--
Fred Cisin cisin(a)xenosoft.com
XenoSoft http://www.xenosoft.com