[HECnet] Silly RSX questions....

[Johnny Billquist]

On 2012-07-09 03:21, Paul_Koning at Dell.com wrote:

On Jul 8, 2012, at 9:01 PM, Bob Armstrong wrote:

I don't know if you understand the concept of memory partitions in RSX
properly.

  No, I guess not.   The usefulness of partitions in an unmapped system is
easy to see - since tasks have to be linked (er, "TKBed") to run at a
specific virtual address and all tasks have to share the same address space
at the same time, you have to fit the tasks into memory.   It's really the
address space that's being partitioned as much as it is the memory.   The
concept is not unlike overlays.

  But once you have an MMU the whole procedure is pointless.   Every task and
every processor mode can have its own contiguous virtual address space.
Nobody needs to share virtual address space with anybody else.   And the
mapping to physical memory is (for practical purposes) completely arbitrary
and easily changed on the fly.   What's gained by partitioning physical
memory into fixed chunks that are allocated only to specific uses and can't
be shared?

The point that I know of (having seen it at work in Typeset-11 which is based on RSX-11D or IAS) is to have some critical tasks be guaranteed memory, while others content which each other (but not with the critical tasks).   That simple example results in two partitions, a specific one and a general one.

Right. Which is why DECnet-11M uses a bunch of partitions of its own. In M+ this was solved by actually being able to lock regions in memory.

	Johnny

-- 
Johnny Billquist                                   || "I'm on a bus
                                                                  ||   on a psychedelic trip
email: bqt at softjar.se                         ||   Reading murder books
pdp is alive!                                         ||   tryin' to stay hip" - B. Idol