9 Nov
1999
9 Nov
'99
10:44 a.m.
CLASSICCMP(a)trailing-edge.com wrote:
Can RT-11 deal
in any way with an RA92?
Yep, it sure does. RT-11 will deal with drives up to 8
Gbytes by use of the
SET DUn:PART=nnn partitioning method. How you keep track of what's
in all 256 partitions is your business :-). Even larger drives can be used with RT-11, but you
only get to use the
first 8 Gbytes. I've got a RT-11 5.7 system here with a 9.1 Gig
Micropolis drive attached.
In regard the the maximum size of the drive, the DEC implementation
allowed a partition number of 377 Octal (255 decimal) as the maximum
since the two word table uses the UNIT for the first word and the
second word split (one byte each) between the partition and the port
(controller) which is almost a complete waste since the DEC
implementation allows only a maximum of four ports in any case
(only 2 bits required). Since all 16 high order bits of the 32 bit block
number are available, it would be possible (but not trivial) to allow
a much larger partition number and make better use of the map table.
Since I don't have a 9.1 GByte Micropolis (slurp slurp slurp) for a
system with RT-11, I have not bothered to determine how much
effort it would be. Tim, maybe you could figure out what code
references the PART and PORT values and see if the 2 bits in
use for the PORT could be placed at the top of the word and
6 extra bits made available to the PART for a maximum number
of 16384 partitions and a 512 GByte drive. While a 512 GByte
drive is not yet available, that should be enough for RT-11. I don't
know how I would keep track of 16384 partitions??????
If you really wanted to go for broke, why not switch the UNIT
and PART values (word for a byte) and allow up to 65536
partitions and a 2 TByte drive.
ALSO, be aware that ONLY for first EIGHT map entries in the
table can be booted with DEC distributed software and presumably
V5.7 from Mentec as well. Changing the map table in the boot
portion of the device driver is not only possible, but has been
done to allow all 64 partitions on a single controller to be bootable
from a software point of view. It is not currently
possible with
DEC boot ROMs to boot an MSCP device where the physical
UNIT number is not the same as the logical unit number in the
mapping table. So if the physical drive UNIT number is 3, DU3:
MUST be booted if you are using a standard DEC distribution
of MSCP or DU(X).SYS device driver. It is also possible to
use a different set of letters for the MSCP device driver (but
start each different one with a letter different from D and L and
from each other if you want more than 8 partitions).
In that case,
the same restrictions apply. The standard DEC boot ROMs will
automatically search for alternate MSCP CSR addresses and
boot MI0: (if Tim had called his driver MI for Micropolis) and
had used ONLY one controller and the drive on the controller
or host adapter was UNIT=0 for the hardware. NOTE THAT
DEC BOOT ROMs FOR A HARDWARE BOOT CAN
NOT BOOT NON-ZERO PARTITIONS.
Note that the above is not quite true if 2 active partitions (the first
must be PART=0) are available. The secondary boot block can be
read from the first drive with UNIT=n for DUn: and the mapping
tables used for the actual partition which is to be booted. I don't
really consider that a proper procedure, but it could be used in
an emergency or even all the time if someone wanted to do things
in a non-standard fashion. I just do not feel comfortable with that
kind of thing since I want to be able to know exactly what will happen.
It is difficult enough to keep track of what is normal. I recommend
that dual partition booting not be done.
Tim, do you have the search algorithm for alternate CSR addresses
when the standard CSR DU MSCP address of 172150 is either
not available at all or is a removable floppy with no media present?
One of these millennia I want to write an MSCP boot interface that
will allow any controller CSR, any UNIT and any PART, but I
can get by with what is available right now - I just boot MI0: and
then re-boot M45:
Sincerely yours,
Jerome Fine