1.44M floppy on Color Computer (was Re: Ebay reaches new low)

From: Roger Merchberger <zmerch_at_30below.com>
Date: Thu Nov 11 20:44:49 1999

Rumor has it that Tony Duell may have mentioned these words:
>> Another factor, the sectors for DOS formatted disk are
>> 512 bytes long. Any loop that only does 256 won't make it.
>> It would need to be formatted with more wasteful 256 byte
>> sectors. This has been a good line of thought ;)
>Is this a problem? Firstly, who says you'd use an MS-DOS format -- the
>CoCo uses 256 byte sectors for virtually everything, and I'd suggest
>keeping to that on the HD disks, just having more of them. As to being
>more wasteful, well, MS-DOS 360K (and 720K) disks fit 9 512byte sectors
>on a track, the CoCo fits 18 256byte sectors. Looks the same to me.
>And the 6809 index registers (X, Y, etc) are 16 bit registers. The loop I
>posted (and the ones others have posted) will transfer 512 bytes if you
>want them to. Whether there's a speed penalty when you cross a 256 byte
>boundary I don't know -- I don't remember anything like that in the 6809
>instruction set, but it's been many years.

The only time you'd see any type of a speed drop from crossing a 256-byte
boundary w/the 6809 is if you were using Direct Page addressing and had set
the DP register... once you got ready to cross a boundary, you'd have to
re-load the DP reg. to continue using the DP addressing. X & Y (& U & S)
are all 16-bit index regs (yes, U & S are stack pointers, but they can also
be used as index regs) so the DP reg doesn't come into play here.

512 byte MS-DOS sectors shouldn't be too hard to implement in software...
if, of course, you had the nitty-gritties to programming the FDC (which the
disk Basic unravelled would provide) and MS-DOS's track format layout...
(anybody got that handy?)

Thanks, and this *has* been fun reading... ;-)
I've learned a lot!
Roger "Merch" Merchberger
Roger "Merch" Merchberger   ---   sysadmin, Iceberg Computers
Recycling is good, right???  Ok, so I'll recycle an old .sig.
If at first you don't succeed, nuclear warhead
disarmament should *not* be your first career choice.
Received on Thu Nov 11 1999 - 20:44:49 GMT

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