This may be of general interest, or if not, at least it will go into the mailing list archive.. some Alto file extensions Alto file names are case-independent .run executable file .cm command file (executive instructions, like CP/M batch files) .boot bootable file .d BCPL definition file (like C .h files) .bcpl BCPL source file .syms BCPL symbol file .asm Alto assembly language source file .mu Alto microcode source file .br BCPL binary file .decl BCPL declarations file (same as .d) .al Alto font file .bravo Bravo text file .press Press document file .mesa Mesa source file .bcd Mesa binary file .image Mesa executable file .draw Draw document file .log Log files .st Smalltalk source file Since XDE is a descendent of the Alto Mesa environment, many of the extensions (.cm .mesa .bcd) carried forward onto D machines.