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Technique for Relocatable Chains

IP.com Disclosure Number: IPCOM000074985D
Original Publication Date: 1971-Jul-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 57K

Publishing Venue

IBM

Related People

Holloman, DR: AUTHOR

Abstract

The feature described is a technique for using relocatable, relative addressing for chaining data. It is applicable where data must be chained and the data is subject to transfer from one medium to another, or the location within the medium is subject to change. For example, a process obtains data of various types, classifies it, and stores it by type. The amount of data of each type is unknown at the start of the process and is highly variable (i.e., some types may have hundreds of records while others may have a few or none). Thus, the data may be best stored as intermingled chains within a directly accessible storage medium instead of in preallocated space for each data type. Additionally, if addresses used for chaining are in the form of a displacement and a reference to a base, thin the addresses are relocatable.

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Technique for Relocatable Chains

The feature described is a technique for using relocatable, relative addressing for chaining data. It is applicable where data must be chained and the data is subject to transfer from one medium to another, or the location within the medium is subject to change. For example, a process obtains data of various types, classifies it, and stores it by type. The amount of data of each type is unknown at the start of the process and is highly variable (i.e., some types may have hundreds of records while others may have a few or none). Thus, the data may be best stored as intermingled chains within a directly accessible storage medium instead of in preallocated space for each data type. Additionally, if addresses used for chaining are in the form of a displacement and a reference to a base, thin the addresses are relocatable. This permits moving the data from one storage medium to another or within a storage medium. Allocation of storage can be made as required.

The elements and relationships of the technique are:
1) A table 1 of absolute addresses of areas of allocated storage

medium is maintained.
2) A relative address or chain address 2 for a type of data

consists of an index 3, to an address within the table 1 of

absolute addresses plus a displacement 4 to a point within

the area of allocated storage medium.
3) A relative address 2 is maintained in a table 5 for each data

type as a pointer to the first element in the chain for that

type.
4) A chain element 6 consists of the relative address 7

(analogous

to address 2) of the next element 6 in the chain (if any more

elements) and the stored data 8.
5) The absence of a relative address indicates the end of a chain. Mode of Operation.

To access data of a given type, the steps are:
1) Get the relative address 2 of the first chain element from the

table of data types 5.
2) If there is no relative address 2 or 7, this is the end of the chain - exit.
3) The index 3 is used to reference a value in the table 1 of

absolute addresses which points to a storage area. This

address 1 is the base for the chain element.
4) Add the displacement portion 4 of the relative address 2 or 7

to determine the absolute address of the next element of the

chain.
5) If the desired information has been located, exit; otherwise

return to step 2 and continue following the chain.

Example of Usage.

The following assumptions are made:
1) The sample program is written for use in an IBM S/360.
2) The prime storage medium is core memory. The data may be

written

to disk for long-term storage and read back into core at a

1

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different location for subsequent processing.
3) Each entry in the table 1 of absolute addresses is four bytes

wide on a word boundary. The low-order three by...