Looking for a ST419

Jules Richardson jules.richardson99 at gmail.com
Fri Oct 31 12:12:10 CDT 2008


Chuck Guzis wrote:
> On 30 Oct 2008 at 17:44, Jules Richardson wrote:
> 
>> I think the end of the last discussion on this resulted in the conclusion that 
>> it could be done, but required frequencies high enough to rule out just 
>> slapping some TTL together on a bit of prototype board...
> 
> ISTR the bitrate from a ST412 drive was about 5 MHz, or one bit every 
> 200 nsec/8 bits per 1.2 usec.  That doesn't seem to be all that high 
> to me--at least not in terms of today's logic.  I think I remember 
> that RLL 2,7 drives had to be able to handle 7.5 MHz data.

Sure, but I believe one of the assumptions was that it'd be useful to 
oversample the data and decode in software (possibly as an aid in error 
recovery, possibly to make the hardware independent of data encoding used - I 
don't remember which).

That ends up pushing things into tens of MHz, and I suspect there's quite a 
few people who can happily throw LS-TTL logic onto a bit of breadboard but who 
don't have the experience or equipment to make something running at that sort 
of speed.

Perhaps I'm completely misremembering, though, and mixing up a device which 
can archive a drive from a device which emulates such a drive (and it's only 
the emulation which needs the oversampling aspect)

Related note: I think there's a whole range of data recovery devices / 
techniques that are worth thinking about (not only just with hard drives) - I 
keep wondering if a separate discussion medium for such topics would be 
useful, along with the support of various computer museums, but then we know 
how people can't generally agree on anything when it comes to some of these 
things :-)  Seems a shame both that there's a wealth of info scattered around 
out there that could in theory be collected together, and that separate groups 
could easily end up doing the same tasks in parallel.

cheers

Jules




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