PDP-1-X microtape format

The PDP-1-X time-sharing system used a file system for storing data on microtapes. Microtapes could also be stored in a drum area, from which they could be written to 7-track magnetic tapes.

The two main data structures on a tape are the directory and the block table. There is just one directory listing all file names and pointing to the first data block in the file. However, the files are arranged in a hierarchical manner which can be viewed as a system with subdirectories. The block table has a link to the next block for all blocks on the tape.

There are two versions of the file system. The older version only stored 512 blocks on a tape. The newer version stores 576 blocks; for this to work, the directory and block table are expanded in size and moved to another location.

External links

• http://www.bitsavers.org/bits/MIT/rle_pdp1x/dectape/ - Microtape images.
• http://www.bitsavers.org/bits/MIT/rle_pdp1x/magtape/ - Magtape images.