On Sun, Dec 3, 2017 at 10:44 PM, Sudershan Ravi <[email protected]>
wrote:
> Hi,
> Why do we use access registers?
>
"Because they're there!" {lame joke}
Peter referred you to the Principles of Operation. That book will never
make the "best seller" list, as excellent as it is. The place to start is
Chapter 3: Storage (in my version that's page 3-23). The manual itself is
here: publibfp.dhe.ibm.com/epubs/pdf/dz9zr011.pdf .
Another good place to read is "z/OS MVS Programming: Extended Addressing
Guide". That's here:
https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.2.0/com.ibm.zos.v2r2.ieaa500/duna.htm
. In some ways, it is an easier way to get a handle on access registers.
Especially in a z/OS environment. I don't know z/VSE, but I'll bet there is
an equivalent manual for how to use them in it around somewhere.
If you're an old time Intel programmer, you may remember "segment
registers" in the 8086 time frame. If so, and you're not too concerned
about reality, you can think of an access register as something akin to a
segment register. But it's more like an indirect pointer. That is an access
register is a value which relates to an entry in the DUCT which "points" to
another address space. The PoPS above refers to this as an ASN and doesn't
reference the DUCT because that is a z/OS "thingie".
--
I have a theory that it's impossible to prove anything, but I can't prove
it.
Maranatha! <><
John McKown
