AMOS organizes disk space into physical devices, logical units, and a pair of octal numbers referred to as the "p,pn" for "programmer, project number.". Within this structure are the files, which consist of a one-to-six character name and a one-to-three character extension. The characters used in filenames are from the "RAD50" set, which consists of 0-9, A-Z, and $. No part of the filespec is case sensitive. For example, the following are equivalent:
DSK0:COPY.LIT[1,4]
dsk0:copy.lit[1,4]
Dsk0:Copy.Lit[1,4]
In these examples, the physical device is DSK, the logical unit is 0, and the PPN is [1,4]. The file name is COPY and the extension is LIT.
Under AMOS, a logical unit was essentially a partition within a physical disk device, more or less equivalent to a drive letter under Windows. Within each logical unit, there were individual directories identified by a pair of octal numbers (each ranging from 0-377) referred to as a "PPN" (Project, Program Number). Individual directories (i.e. a PPN within a logical unit within a physical unit) could also be assigned aliases, called ERSATZ devices, which have the syntax of device names. This is similar to the situation under Windows where a drive letter can be mapped to another directory. These ERSATZ devices are defined in a text file DSK0:ersatz.ini[1,4]. You can add your own; each one must consist of up to six "RAD50" characters starting with an alphabetic character.
