Olivetti 3MB ST506-interface drive?

I don't recall how many heads a ST506 had. I have one on my NC4000, home brew, machine. I recall picking the drives up at garage sales because DOS no longer supported them, only being 5Meg. Next time I at my storage, I can being my machine home and power it up. I suspect it has the setup information in my source code. I used an old XT HD controller card for the hard drive and a XT floppy card for the floppy. I disabled the EPROM on the HD card because it was useless for the NC4000. The M20 used the 11Meg ( I guess formatted 10 Meg ) drives. I used a ST251 because it had the same number of heads (6) and RPM speed as the Olivetti drive used. It had more cylinders but that wasn't an issue. Dwight ________________________________________ From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Fred Cisin <cisin at xenosoft.com> Sent: Sunday, March 13, 2016 3:13 PM To: General Discussion: On-Topic and Off-Topic Posts Subject: Re: Olivetti 3MB ST506-interface drive? Is that "3MB" FORMATTED, or UNFORMATTED capacity? "10MB" (ST412) was 12MB unformatted, with 306 cylinders and 4 heads. "5MB" (ST406) was 6MB unformatted, with 306 cylinders and 2 heads. or was it (St506?) 153 cylinders with 4 heads? In any case, using half as many heads/surfaces would create an "ST503" drive. about 2.5M formatted capacity.