Block allocation map

File:View BAM.gif

Here, the View BAM utility on the Commodore 1541 Test/Demo Disk is displaying a portion of the block allocation map for that disk.

In computer file systems, a block allocation map (BAM) is a data structure used to track disk blocks that are considered "allocated" or "free for writing."

Very rapid file access was made possible by consulting a Block Allocation Map only when it absolutely had to (that is, when writing), and ignoring it when reading. This effectively made writing to the disk more time consuming than reading.

In terms of Commodore Business Machines compatible Disk Drives, the BAM was located at a different physical track and sector on each of the Commodore 1541, Commodore 1571, and Commodore 1581 disk drives.

See also