ISAM (Indexed Sequential Access Method)

ISAM (Indexed Sequential Access Method) is a file management system developed at IBM that allows records to be accessed either sequentially (in the order they were entered) or randomly (with an index). Each index defines a different ordering of the records. An employee database may have several indexes, based on the information being sought. For example, a name index may order employees alphabetically by last name, while a department index may order employees by their department. A key is specified in each index. For an alphabetical index of employee names, the last name field would be the key.

ISAM was developed prior to VSAM (Virtual Storage Access Method) and relational databases.

This was last updated in November 2005

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ISAM: I use many Flat Files, with fixed-length records, and "text" fields, working in tandem with Perl SDBM binary files of key/value pairs tied to Perl program hash tables. These key/value pairs offer persistent, instantaneous, random access to Flat File records. For random access, the file pointer is first set to a single record location byte offset, where the offset is the number of bytes to seek to from either TOP of file or END of file. Then the record is read into memory. Once in memory, the contents of the record can be changed/modified and written back out to the Flat File, overwriting the existing data stored in that record. NO SQL (ISAM) is faster than SQL because it does not use a query optimizer. THIS IS FREE DB TECHNOLOGY FOLKS !!! AND YOU DON'T NEED A HIGHLY SKILLED DBA TO MAINTAIN IT. NO DATA ACCESS COMPONENTS HAVE TO BE INSTALLED EITHER.
Joint Database Technology
Using Flat File, fixed-length record databases in tandem with binary SDBM database files of key/value pairs tied to program hash tables for persistent random access indexing to Flat File records by the information contained within the fields of the Flat File records.
I use: indexed relational "text" flat file databases (many 128-GIG flat files, or larger, with 100's of millions of records each, or even billions each), indexed by persistent external binary PERL DBM database files of key/value pairs, tied to in-memory PERL program hash tables at run-time, where the KEY is 1 or more fields and/or partial fields contained within the flat file records, and the VALUE is the byte offset location of a record, used for setting the position of the file pointer before performing READ/WRITE operations upon a record in any of the relational flat files.  Custom word-to-code key mapping of data for compression/encryption is utilized, or formula-based MIMEbase64.   Database native Windows(tm) GUI user-interfaces are written in ActiveState ActivePerl for Windows 5.26.1 (the latest) for accessing the shared flat file system. 

Supported are:   Unique Primary Key, Unique Alternate Keys, and Alternate Keys with Duplicates (1000's of duplicates, or many more), Parent-Child 1-to-Many record relationships, and Look-ups to remove redundant data from the databases (e.g. look-up part-description via part-number, etc.).