9 Nov
1999
9 Nov
'99
11:01 a.m.
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.
Sure, this is done fairly easily. You have to modify not only the
SET overlay usage inside the DU handler, but also the parts of RESORC.SAV
responsible for SHOW DEV:DU. (Working from memory, the relevant parts
are in RESDEV.MAC on the source kit - I was fooling around with this
earlier this year to add multi-CSR display capability.)
The real question is, will I ever have so much RT-11 software/data that
I need access to more than 8 Gbytes? I've got a wall of 8" floppies here,
over 7000 floppies in total, but all 7000 floppies together (even assuming
double density) are only 3.5 Gbytes! (And less than half of those 8" floppies
are RT-11 stuff in the first place - the rest being WPS/8 and CP/M stuff.)
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?
The "DEC standard" way of determining alternate CSR's is to follow
the autoconfigure rules (see
http://metalab.unc.edu/pub/academic/computer-science/history/pdp-11/hardwar…
for a nice writeup of how the rules work). Unfortunately the RT-11
developers chose to ignore these rules in picking their "default" second
CSR for RT-11, but of course you could choose to follow these rules
by ignoring the SYSGEN-suggested secondary (and tertiary and whatever
comes after) DU CSR's.
--
Tim Shoppa Email: shoppa(a)trailing-edge.com
Trailing Edge Technology WWW: http://www.trailing-edge.com/
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