Roshan George

• Mar 10th, 2006

 

Addressing mode specifies the architecture used, ie 24 bit addressing mode or the 31 bit addressing mode,ie, Amode=24 or Amode=31.

The residential or Rmode is used to specify whether or not the job exists above or below the 16Mb line, ie, where it is resident.

kckinney

 Profile Answers by kckinney Questions by kckinney

• Sep 3rd, 2010

 

These both have to do with the location of memory relative to the 16meg "line"
AMODE(32) means the program can access program defined storage above the line.
RMODE(32) means the program itself can reside in storage above the line.

This was added when mainframes started supporting memory using 4 bytes instead of the previous 3 bytes.  This greatly increased the amount of storage.
Initially, using 32 was a quick way of getting a lot of memory.  Eventually everyone started using it.  Today it's pretty much assumed you're using 32 as memory below the line is very constrained.

But today it's not that simple.  z/OS supports 64 bit execution.  This means it can access  memory above the 2gig limit imposed by 4 byte memory addressing.
The 2gig limit is now called the "bar".