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Btrieve is a database developed by Pervasive Software. The architecture of Btrieve has been designed with record management in mind. This means that Btrieve only deals with the underlying record creation, data retrieval, record updating and data deletion primitives. Together with the MicroKernel Database Engine it uses ISAM, Indexed Sequential Access Method, as its underlying storage mechanism.
Btrieve is essentially a database that uses keys and indexes to organise data. However, the file structure itself is largely built around smaller units of data, called "pages" in Btrieve. Though the structure has changed over the various versions of Btrieve, the file structure still revolves around a File Control Record (FCR) — which defines the configuration of pages — and pages in the Btrieve file that contain data. Historically, Btrieve used "physical pages", or pages that were located at fixed positions in the file. Beginning with version 6.0 "logical pages" started to be used, which were mapped to page allocation tables (PATs) — this allowed Btrieve to change their record update technique from what was later known as "pre-image paging" to a technique called "shadow-paging".
Btrieve is committed to backward compatibility, as versions of Btrieve until version 6.15 use a standard file format and, until Btrieve 6.0 was released, were completely backwards compatible. Btrieve 6.0 introduced new features and had to break compatibility with older versions of the software to implement more advanced features. The API likewise remained backwards compatible, with only one feature (split files to separate media) being dropped. At one point, Btrieve's former CEO Ron Harris stated that "The version 1.0 API is still supported in version 6.15, and we're going to keep it forever!"[1]: 11 .