binary file. This results in a set of logical file types identified by three letters, e.g. Logical Sequential Text is LST. The logical file types are LST, LSB, LRT, LRB. The converse to logical files are physical files, which are accessed block at a time, and these are known as Physical Random Binary (PRB) files. File types PST, PSB, PRT also exist in theory, but have the same capabilities as PRB and are not generally used. Additionally, there is a Logical Indexed Sequential (LIS) filetype, which is an ISAM file and always appears to be sorted on its key field, and a Byte stream (BYT) filetype, which was added in Rel 6.5 to better support the OS4000 NFS server. A filetype CAT is used to hold catalogues—it is actually the same as an LSB file, but can only be modified by the filesystem itself. In addition to files and catalogues, there are 3 types of symbolic links. References (REF) can be created to point to another file or catalogue which creator of the REF can see through an initial context pointer, in either the same filesystem or another filesystem. Off Disk Pointers (ODP) are similar to references but can be created to point to a file or catalogue which cannot be seen through any initial context pointers, and creating an ODP is a privileged operation only available to the system manager. Support for Unix style symlinks (arbitrary text stored in a catalogue) was added in Rel 6.5 to better support the OS4000 NFS server, but symlinks can only be created and are only visible from NFS clients. OS4000 also provides a non-hierarchical temporary filesystem. This supports exactly the same types of file as permanent filesystems, except for CAT, REF, ODP, and symlinks. The file contents are stored in dedicated temporary filing disk regions, but the file metadata is stored in memory. Each logged in user has a private temporary filing name space which cannot be seen by any other logged in user (nor even another logged in user with the same username). A user's temporary files are deleted when the user logs out (and implicitly if the system is rebooted). Temporary filenames start with a percent "%" or ampersand "&" and are limited to 8 characters. Multi-access Environment The following shows a short Multi-access login session: In this case, user SMAN has logged in and issued the EXAMINE command. Then