What's a floppy CBM 2030? What are the differences to a 2040?

From: Hoffmann-Vetter, Martin <*martinhv_at_arcor.de*> Date: Tue, 30 Aug 2011 01:47:08 +0200 Message-ID: <000301cc66a5$fb5265e0$1b09a8c0@mhvnb10> · martinhv_at_arcor.de

Hello,

i've read the "More about the CBM 4040 DOS" from Gary van Beeck (you found
the fully documented assembler listing at bombjack.org). At two pages, he
write about the double density 2040 format (2A) and a 2030 format (2B). The
next known format 2C is the quad density format for the 8050.

But what is a CBM 2030? One difference i found is the count of sectors per
track.

Track  2040  2030
31-35   17    14
25-30   18    15
18-24   19    16
 1-17   21    18

So the user useable numbers of secors would be 562 (2030) and not 664
(2040).

That's all for a DOS version 2 (also known as 3040/4040). The DC (901466-04)
writes $0F at $0400 (DC) or $1000 (BC) memory location to identify the 2040
format id. The DOS expected a $64 for the 2030 format id. So for the DC it
must be an other code. Possibly 901466-03?

Other differences are the gap after the sector header (9 for 2040 and 28 for
2030) and the minimum bytes between sectors (2 for 2040 and 30 for 2030).

Who knows about a floppy CBM 2030 or the disk format 2B?

Martin

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