[Coco] Dead (??) 5 1/4" drives

[Mathieu Bouchard]

Le 2017-03-08 à 08:44:00, Mathieu Bouchard a écrit :

> Le 2017-03-06 à 23:50:00, Barry Nelson a écrit :
>
>>> I have 2,  5-1/4 drives, of which one can go. ( keeping at least one for 
>>> myself).
>>> I do think they are both DS 80 track drive's, and they where given to me 
>>> from e working setup.
>>> If you are interested in one let me know.
>>> I think that $20 + Shipping would be a reasonable price.
>> 
>> DS 80 track? That would make those 720k drives.
>
> Nope, because 3.5" DS 80-track includes three different densities : 720k, 
> 1440k, 2880k. They are distinguished by number of sectors : 9, 18, 36 (with PC
> formatting @ 512-byte/sector).

Woops, sorry for the dumb mistake about disk size. 5.25" DS 80-track include two 
different densities, QD and HD. Almost all those disks are HD, formatted at 
1200k (15 PC sectors). QD disks are listed as 640k (8 PC sectors) on Wikipedia, 
not 720k (9 PC sectors). I don't know why. I have never seen any. I can only say 
that 8-sector formatting was the norm in MSDOS 1.x, so it seems to me like a 
format that was dropped very early. Using the "physical composition" section of 
the article, it seems like it could be doing 720k if using a formatting 
analogous to the 360k (72% of unformatted size), or 800k if formatted like a 
1200k (80% of unformatted size).

https://en.wikipedia.org/wiki/List_of_floppy_disk_formats

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| Mathieu BOUCHARD --- tél: 514.623.3801, 514.383.3801 --- Montréal, QC