idea for a universal disk interface

[ben]

On 2022-04-16 1:13 p.m., 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.
> 
> Tom
> 
How do you handle the disk hardware timing, power up, seek
and disk RPM?. Ben.