Re: Q:400k disk = Which blocks?

[nparker@cie-2.uoregon.edu (Neil Parker)]

In article <560f31$5u8@login.freenet.columbus.oh.us>
dalloff@freenet.columbus.oh.us (Dave Althoff) writes:
>Okay, so I want to directly access a 400k 3.5" disk using the ProDOS block
>read command.  Can anyone tell me which blocks I need to read?  Is it, for
>instance, all odd-numbered blocks, all even numbered blocks, the first
>half of the disk...or what?

Assuming you're using a device that supports 400K disks (I have a vague
recollection that the Unidisk 3.5 doesn't), just give READ_BLOCK a block
number in the range 0...799--i.e. treat the disk as if it occupied the
first half of an 800K disk.

The actual physical relationship between block numbers on a 400K disk and
block numbers on an 800K disk is a lot more compilated than that, but the
interface firmware automatically recognizes 400K disks and performs the
necessary translations transparently.

               - Neil Parker
-- 
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