Browse Prior Art Database

Two Level Access List

IP.com Disclosure Number: IPCOM000107524D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 74K

Publishing Venue

IBM

Related People

Howarth, RJ: AUTHOR [+2]

Abstract

The IBM System/390* (S/390*) central processing unit (CPU) provides a means for programs to access data in multiple virtual address spaces called access register addressing. This means defines a process called Access Register Translation (ART), where the contents of an access register are used to locate the segment table of a virtual address space that a program wishes to access. The access register translation process utilizes a table called an Access List (AL) to perform the translation from the contents of an access register (the contents being called an Access List Entry Token, ALET) to locate the segment table of the address space that the program wishes to access. Currently, the S/390 CPU describes the access list as a single-dimen sion or single-level list of entries residing in the real storage of the machine.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Two Level Access List

       The IBM System/390* (S/390*) central processing unit
(CPU) provides a means for programs to access data in multiple
virtual address spaces called access register addressing. This means
defines a process called Access Register Translation (ART), where the
contents of an access register are used to locate the segment table
of a virtual address space that a program wishes to access.  The
access register translation process utilizes a table called an Access
List (AL) to perform the translation from the contents of an access
register (the contents being called an Access List Entry Token, ALET)
to locate the segment table of the address space that the program
wishes to access.  Currently, the S/390 CPU describes the access list
as a single-dimen sion or single-level list of entries residing in
the real storage of the machine.  The maximum number of entries in
the access list is either 1024 or 4096 entries depending upon model.

      This article describes a two-dimension or two-level access
list.  The index used by the CPU to select an address space during
the ART process is called the Access List Entry Number (ALEN).  The
ALEN is the right most 16 bits of the ALET.  The ALEN is divided into
two parts, an Access List First Table Index (ALFTX) and an Access
List Second Table List (ALSTX).  During the ART process, the ALFTX is
used to select an entry in an Access List First Table (ALFT).  The
ALFT is located by the existing S/390 mechanism used to locate the
one-dimension access...