Art of Assembly Language, 1st Edition

8.5. 8.5 ISAM (Indexed Sequential Access Method) Files

ISAM is a trick that attempts to allow random access to variable length records in a sequential file. This is a technique employed by IBM on its mainframe data bases in the 1960s and 1970s. Back then, disk space was very precious (remember why we wound up with the Y2K problem?), and IBM's engineers did everything they could to save space. At that time disks held about five megabytes or so, were the size of washing machines, and cost tens of thousands of dollars. You can appreciate why they wanted to make every byte count. Today, database designers have disk drives with hundreds of gigabytes per drive and RAID^[134] devices with dozens of these drives installed. They don't bother trying to conserve ...