Troubleshooting
Problem
This document describes some of the terms and definitions used in SLIC.
Resolving The Problem
Terms and Definitions
| Address: | The location in the storage of a computer where particular data is stored. |
| Real Address (storage): | Main Storage. |
| Virtual Address (storage): | An addressing scheme that allows external disk storage to appear as main storage. |
| Temporary Address: | An address used to locate a piece of data that does not survive an IPL. |
| Temporary Library: | A library that is automatically created for each job to contain temporary objects that are created by the system for that job. The objects in the temporary library are deleted when the job ends. The system name for the temporary library is *QTEMP. |
| Temporary Objects: | Objects, such as data paths or compiler work areas, that are automatically deleted by the system when the operating system is IPLed. |
| Permanent Address: | An address used to locate a piece of data that does survive an IPL. |
| Segment Identifier (SID): | Refers to the 4 or 5 high-order bytes of an 8-byte virtual storage address. The Big SID is composed of a 5-byte SID and 3-byte offset, which encompasses an address range of 16mb with 4096 4K pages. The offset contains first the Page ID (PID) for 1.5 bytes then is followed by the Byte ID (BID) for 1.5 bytes, which points to bytes within a page. The Little Sid consists of 5 bytes called the Segment Group Identifier (SGID), which addresses 16MB of storage. One SGID consists of up to 256 little SIDs, each of which addresses 64K of storage. The number of little SIDs is expressed in byte 5 (bits 40-47) of the address. The first half of byte 6 (bits 48-51) identifies one of the possible 16 4K pages within a little SID. The last 1.5 bytes (bits 52-63) are the BID. |
| Permanent Directory: | Used by Storage Management to keep track of permanent addresses currently being used and their corresponding locations on DASD. |
| Temporary Directory: | Used by Storage Management to keep track of temporary addresses currently being used and their corresponding locations on DASD. |
| Free Space Directory: | This is a pageable machine index which tracks all unassigned sectors on all DASD units (CISC systems only). |
| Static Directory: | Used to store VLIC persistent data such as the DASD locations of the Permanent Directory, and so on. |
| Auxiliary Storage Pool (ASP): | A group of units defined from the disk units that make up auxiliary storage. ASPs provide a means of isolating certain objects on a specific disk unit to prevent the loss of data due to disk media failures on other disk units. There is a System ASP, which is always ASP1, that LIC and IBM OS/400 or IBM i5/OS must be installed on and up to 98 other ASPS, termed user ASPs. |
| Main Storage Pool: | A division of main storage, which allows the user to reserve main storage for processing a job or group of jobs, or to use the pools defined by the system. Up to 16 pools can be set up. |
| Sector: | An area on a disk track or a diskette track to record information. The smallest amount of information that can be written to or read from a disk or diskette during a single read or write operation. Consists of 512 Bytes of data + 8 Bytes sector header to give a total size of 520 bytes. There are some other bits that belong to hardware, but they can be ignored for the purposes of storage management. |
| Extent: | Variable-sized piece of DASD to which a virtual address range has been assigned. |
| Page (noun): | Made up of 8 sectors of DASD (4KB) or 4KB of main memory. |
| Page (verb): | Move a page of data from main memory to DASD or vice versa. |
| Teraspace: | Teraspace is a large temporary space that is local to a job. A teraspace provides a contiguous address space however may consist of many individually allocated areas, with unallocated areas between. Teraspace exists no longer than the time between job start and job end. A teraspace is not a space object. This means that it is not a system object and that you cannot refer to it by using a system pointer. However, teraspace is addressable with space pointers. |
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Historical Number
8013008
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Document Information
Modified date:
14 October 2024
UID
nas8N1010239