Datacom usage of the ASVT in 24- or 31-bit mode

Products

• Datacom
• Datacom/AD
• Datacom/DB

Issue/Introduction

z/OS V3R1 now recommends that the Address Space Vector Table (ASVT) be placed in 31-bit storage, instead of requiring 24-bit as with previous release levels.

Will Datacom have any problem using a 31-bit address for this?

Resolution

After reviewing the Datacom software code, we have found that Datacom accepts the ASVT as either a 24-bit or a 31-bit address. 

Consequently, there is no problem with Datacom/AD and Datacom/DB using either value for the ASVT.

If you want to monitor the location of the ASVT, you can use the IBM Health Check for Supervisor checks, and specifically, the SUP_ASVT_ABOVE_16M check. You can also find information about the location in the DIAGxx IPL member, where you would look for the list containing IHAASVT.

If you are using the SYSVIEW product, you can display this DIAGxx information using the "XMVS D DIAG" command. The SYSVIEW comands ASADMIN and ASLIST will show the contents of the ASVT, but do not indicate if the anchor is located in 24- or 31-bit memory (you can review the SYSVIEW Help panels for these by issuing the "Help ASADMIN" and "Help ASLIST" commands, respectively).