Holger B. Austinat writes:
> > Now, I have not found the "dimensions" on an RD53 - don't
> > know number of cylinders...help please.
> 
> Here is the section of /etc/disktab from the NetBSD-distribution telling 
> you the parameters you need:
> 
> rd53|RD53|DEC RD53 on Microvax:\
> 	:ty=winchester:ns#18:nt#8:nc#963:\
> 	:dt=MSCP:\
> 	:pa#15884:oa#0:ba#8192:fa#1024:\
> 	:pb#33440:ob#15884:bb#4096:fb#512:tb=swap:\
> 	:pc#138672:oc#0:bc#4096:fc#512:\
[...]
> ns = sectors per track   =  18
> nt = tracks per cylinder =   8 (==> sectors/cylinder = 144)
> nc = number of cylinders = 963

As Ken Wellsch already said, these data doesn't match the physical
geometry which is 17/8/1024. Similiar to SCSI MSCP doesn't access
the disk using the physical geometry but by using LBNs (Logical 
Block Number). Since the MSCP-Controller hides some sectors of the 
disk, the number of sectors (ie. LBNs) available to the user is 
138672 which isn't dividable by 17 nor 1024. 
If you would use the physical geometry then some sectors of the disk 
would be unused. Thus it makes sense to use a s/t/c triple which
doesn't need to reflect physical geometry but uses all available sectors:
	% /usr/games/factor 138672
	138672: 2 2 2 2 3 3 3 3 107
	        \ | / \ | / \ | /
	          8    18    963 

The same holds IMHO for RD54 where /etc/disktab uses the physical
geometry 17/15/1225 while having 311200 available sectors. I'd prefer
	% /usr/games/factor 311200
	311200: 2 2 2 2 2 5 5 389
	        \ | / \ | / \ | /
	          8    20   1945

I don't know if it's possible to define partition boundaries in a 
way that it maps to physical cylinder boundaries. If yes, then it
would make sense to rewrite the /etc/disktab entries for most of the 
MSCP disks. (IMHO these entries are slightly outdated in many ways 
esp. concerning partition sizes/offsets and block/fragment sizes). 
On the other hand now that /edlabel is available as an offline tool
for creating disklabels, /etc/disktab is only used as a reference
for physical/logical geometries?

Ciao,
	bertram