idea for a universal disk interface

[Fred Cisin]

ONCE MORE, I APOLOGIZE.
(details bottom posted)

>>> This was the approach IBM used in it's first RAMAC RAID where I think 
>>> they had to buffer a whole cylinder but that was many generations ago
> (my copy of the specs may not be exact):
> Buffering a whole cylinder, or a whole surface, of the RAMAC was no big
> deal.
> One hundred surfaces (52 platters, but not using bottom of bottommost nor
> top of topmost) totalling to 5 million 6 bit characters.
> That's 50,000 characters per surface.
> OR 50,000 characters per cylinder
> ("square geometry" :-)
> 100 tracks per side of a platter (at 20 tracks per inch) meant about 500
> characters per track
> Problematic in the CP/M days, but such a buffer is small in current usage.

On Sat, 16 Apr 2022, Tom Gardner via cctalk wrote:
> Not the RAMAC of 1956 but the RAMAC Virtual Array of 1996,
> https://www.ibm.com/common/ssi/cgi-bin/ssialias?htmlfid=897/ENUSC96-029&info
> type=AN&subtype=CA&appname=skmwww
> It emulated several different IBM DASD of varying CKD track lengths on fixed
> block HDDs
>
> The trick they used and the one I'm suggesting is they stored an entire
> track, index to index including, gaps, headers, etc, in a concatenated set
> of fixed blocks greater than the maximum length of the raw track.
>
> For example, an SMD drive turning at 3600 RPM and with a data rate of 15
> Mb/sec and a 5% speed variation has a maximum track length of 31,250 bytes
> nominally but never more than 32,895 on the slowest drive.  So allocating 65
> sectors (512 byte) will fit the worst track.  Of course since the emulator
> doesn't have any speed variation only 62 sectors need be allocated per
> track.
>
> I poked around in some old Disk/Trends and it seems the largest ESDI/SMD
> drive was on the order of 2.5 GB which is likely a formatted capacity so a
> full drive emulation might require a maximum of 3.3 GB which is well within
> the size of a modern PC and given the memory data rate I suspect an emulator
> wouldn't have to buffer more than two memory words.

THAT is an fascinating project!


"Never mind" - Emily Litella (Gilda Radner)
I need to step back and BUFFER my replies for a period of time.
It seems that almost everything that I reply to, I misunderstand some part 
of what I am replying to, and need to apologize.


As a mitigating factor, in this same thread, I had mentioned owning a 
RAMAC platter (from 60 years ago), that was too damaged to even consider 
trying to read from, so that I am making a patio table out of it.

I don't consider 1996 to be "many generations ago"
and, You had said buffer a whole CYLINDER.  I wrote a reply assuming that 
you meant TRACK.  When I noticed the cylinder/track confusion, I edited 
my reply to be numbers for a cylinder, but failed to completely edit out 
my comment that buffering the size of an entire [EARLY 1960] RAMAC TRACK 
was no big deal, and was promptly reminded that in the day, buffering 50K 
WAS a big deal.


"Never mind"
--
Grumpy Ol' Fred     		cisin at xenosoft.com