Weird block sizes

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hansliss
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Joined: Sun Mar 18, 2018 10:31 am

Weird block sizes

Post by hansliss » Sun Apr 22, 2018 5:11 pm

I seem to have been given a few CDC Cyber floppies, and had some unexpected trouble reading them properly, until I found this (from http://bitsavers.trailing-edge.com/pdf/ ... _Feb77.pdf):
The flexible disk drive (figure 7-9) is a random-access
device using removable diskettes for the storage medium.
It has a formatted data capacity of 256K bytes when using
the IBM format (128 bytes/ sector) or 280K bytes using
the CDC 1700 format (192 bytes/ sector). The data transfer
rate is 31. 2K bytes per second.
So, is there any way to handle 192-byte sectors with dtc? It seems the sector size can only be chosen from a limited list, which doesn't include 192 bytes.

Or is there any other way of dealing with CDC disks?

ZrX
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Joined: Tue Dec 06, 2011 9:09 pm

Re: Weird block sizes

Post by ZrX » Sun Apr 22, 2018 6:12 pm

I don't think 192 is possible.

Standard formats usually only have a value that defines the usual sizes, 128/256/512/1024.

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mr.vince
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Re: Weird block sizes

Post by mr.vince » Mon Apr 23, 2018 7:45 pm

Non-standard sector sizes either need a modified version of DTC (assignment), or you would have to wait for user defined formats. Third option would be to convert raw to your own format with a converter, e.g. in Python or similar.

hansliss
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Joined: Sun Mar 18, 2018 10:31 am

Re: Weird block sizes

Post by hansliss » Mon Apr 23, 2018 8:18 pm

Ok, thanks. Actually, the python script by Eric Smith that handled M2FM might be able to do this with some modifications. I think it had support for FM and MFM too. I'll look into it later, perhaps.

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IFW
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Re: Weird block sizes

Post by IFW » Thu Apr 26, 2018 4:08 pm

Would be interesting to see stream dumps of such disks.
A generic FM/MFM controller definitely can't handle 192 bytes per sector - it can only use power of 2 sector sizes starting with 128.

hansliss
Posts: 11
Joined: Sun Mar 18, 2018 10:31 am

Re: Weird block sizes

Post by hansliss » Thu Apr 26, 2018 9:30 pm

I haven't confirmed yet if any of those disks were actually written on the Cyber and haven't been overwritten by something else. I'll go through them and check.

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