Editing MUSIC/SP (section)

===File system===
The MUSIC/SP file system was unique in a number of respects. There was a single system-wide file index. The owner's [[userid]] and the file name were hashed to locate the file in this index, so any file on the system could be located with a single I/O operation. However, this presented a [[flat file system]] to the user. It lacked the directory structure commonly offered by [[DOS]], [[Microsoft Windows]] and [[Unix]] systems. In 1990 a "tree-structured" directory view of the file system was overlaid on this, bringing the system more in line with the file systems that were then available. By default the information stored in the files was compressed. This offered considerable saving in disk space. The file system had a fairly sophisticated access control scheme allowing the owner to control who could read, write, append to and execute the file. It also had the concept of a "public" file which was visible to all users and a "private" file which was only visible to the owner.