HLASM - ISK = Insert Storage Key

The opcode of the ISK instruction is X'09'.


  1. Obtain the storage key of a page of real storage.


  1. Register to receive the storage key.
  2. Register containing a page address.


  1. The processor inserts the storage key of the 2K or 4K page addressed by the second argument into the low-order byte of the first argument.
  2. The condition code does not change.

Special Cases

  1. If the page address is not a fullword address the instruction fails. The page address does not have to be on a page-boundary, however; any fullword address within a page addresses the page in its entirety.

Related Instructions

  1. SSK was intended to set the storage key.
  2. ISKE is now used to obtain the storage key of a page of real storage.
  3. IVSK is now used to obtain the storage key of a page of virtual storage.


  1. The ISK instruction was part of the original S/360 instruction set. However, it is no longer supported; it has been replaced by the ISKE instruction. Support for the ISK instruction has been dropped when the 370/XA architecture was introduced.


  1. Independent of Amode or DAT, the page address is always a 24-bit real address.
  2. The storage key was returned in the low-order 8 bits of the 32-bit register specified as the second argument in the following format:
    1. The first 4 bits (0 through 3) were the actual storage key.
    2. If fetch protect was installed (an optional feature on early machines), the fetch-protect bit would be in bit 4.
    3. If DAT was installed the Change and Reference bits would be in bits 5 and 6. I don't know in which order.
  3. Initially the ISK instruction worked on 2K pages only. When 4K pages were introduced, the ISK instruction was modified to address either a 2K page or a 4K page, depending on the address specified and the way that specific page was configured.


Not available (yet).

To the Opcodes Overview.
To the English Homepage for Hlasm.com.
To the General Homepage for Bixoft and Hlasm.com.

This site is a member of WebRing.
You are invited to browse the list of mainframe-loving sites.
Running Tyrannosaurus Rex Dinos are not dead. They are alive and well and living in data centers all around you. They speak in tongues and work strange magics with computers. Beware the dino! And just in case you're waiting for the final demise of these dino's: remember that dinos ruled the world for 155-million years!
Dinos and other anachronisms
[ Join Now | Ring Hub | Random | << Prev | Next >> ]

Below you find the logo of our sponsor and logos of the web-standards that this page adheres to.