Commodore 128 System Manual page 210

Table 12-2. C P /M 3.0 Reserved Filetypes
Filetype
ASM
BAS
COM
HEX
HLP
$$$
PRN
REL
SUB
SYM
SYS
1 2 - 8
Assembler source file
BASIC source program
Z80 or equivalent machine language program
Output file from MAC (used by HEXCOM)
HELP message file
Temporary file
Print file from MAC or RMAC
Output file from RMAL (used by LINK)
List of commands to be executed by SUBMIT
Symbol file from MAC, RMAC or LINK
System file
Meaning