Burnable, patched Microvax-2000 SCSI-boot EPROM images?

David Gesswein djg at pdp8online.com
Fri Sep 24 15:19:20 CDT 2021

On Tue, Sep 21, 2021 at 12:15:12PM -0400, Paul Koning wrote:
> > On Sep 21, 2021, at 12:00 PM, Jonathan Stone via cctalk <cctalk at classiccmp.org> wrote:
> > 
> > The RD53s in both Microvax 2000s are dead. I'm reluctant to buy more 30+ year old rotating media.
> > If I'm going to buy a disk emulator, I'd much prefer SCSI to MFM, for the obvious performance reasons.
> Emulators presumably act, performance wise, like SSDs.  Given that, an MFM emulator will significantly outperform a SCSI hard drive since it has no seek delays.
> David Gesswein's MFM emulator works impressively well and is inexpensive, too.

The MFM emulator can't transfer data faster than the 5 Mbit/second, 
625k Byte/sec of the ST-506 standard. 

Seek time isn't zero due to overhead in moving the data in the Beaglebone
to where the PRU processors can access it. Think its around 0.6ms/head. An
entire cylinder is transfered on each seek. Additional time if cylinder
was written to. Each track written needs to be moved also. Most ST-506 
drives are slower. I'm faster than average seek for RD54 but it wins for 
single track seek at 4ms with 15 heads.

More information about the cctalk mailing list