Copying DEC VAX set up disks rx50, help

[Chuck Guzis]

On 6 Mar 2007 at 8:32, Allison wrote:

> Thats out of context.  

Well, there's been a lot of back-and-forth on this and things have 
been getting all misconstrued.  Allow me to see if I can sort the 
situation out.  I think we've all been trying to say the same thing.

DEC RX50 = 80x1x10x512 = 800K on one side, consisting of 80 tracks 
with 10 512-byte sectors.   Some versions of this format (or the RX33 
corresponding format) leave off the IAM; others keep it in and 
squeeze the sectors together a bit more.

In any case, on a Teac FD55F drive spinning at 300 RPM, the data rate 
is 250 Kbps and takes "360K/180K" type media (Yes, there exist(ed) 
media verified for 96 tpi; so-called "quad" density, but the cookie's 
the same).  It does not take HD media, which has the wrong magnetic 
characteristics (coercivity).

A Teac FD55GFR "1.2MB" drive jumpered to spin at 360K RPM will handle 
this format if the read/write clock is set for 300Kbps.  This is just 
a matter of boosting the clock rate to match the faster spindle 
speed.  The medium remains the same.

Since some variants of this format leave off the IAM and the NEC 765-
type controllers have a "blind" spot right after the index (varies 
according to vendor), the first sector on the track may be 
problematical when reading on a PC (using either the "720K" drive or 
the "1.2M" drives mentioned above).  There are a couple of ways to 
accommodate this.  1) disable the INDEX/ signal from the drive; 2) 
slow the drive a bit to shove the first sector IDAM out of the FDC's 
"blind spot".  Method (1) will not allow for formatting the drive,a s 
the 765 format operation waits for the index pulse (which will never 
come).  Similarly, the READ TRACK operation will not work and a 
"Sector not found" error will cause the FDC to hang and the error to 
be interpreted as a "Not Ready" error.

Have I summarized what's been said accurately?

FWIW, the 10x512 format has been used by many systems.  Some work 
just fine; others have the first sector problem described above.

Cheers,
Chuck