+D filesystem

The +D filesystem was used on the Sinclair ZX Spectrum computer, and with some additional file types, on the SAM Coupé.

+D was a disk and printer interface hardware system used on the Sinclair computer, and its associated filesystem structure was adopted with minor changes on the SAM Coupé, a computer designed to imitate the Sinclair.

The directory takes up 40 sectors (20 kilobytes) on the disk, and is found on the first four tracks of side 1. Subdirectories can also be created, which have the same structure but can be located anywhere on the disk. Directories always are located on contiguous sectors, with the final one having FF (hex) in the last two bytes to indicate the end of the directory. 10 characters are allocated in a directory entry for the filename. The entire entry for a file, including all metadata, is 256 bytes.

Links

 * Wikipedia article on +D device
 * Sinclair UniDOS manual (has appendix with directory structure detail)