casey@CS.UCLA.EDU (08/21/88)
Ok all you PDP-11 gurus, get out your peripheral data books: DEC produced a tape subsystem called a TM-11/TE-10, typically referred to by UNIXers as a TM. The DEC TM was only capable of 800BPI and under. Several third party manufactures have produced TM emulators capable of 1600BPI and even 6250BPI (AVIV only?). 2.9BSD, 4.3BSD, and several other UNIX versions support these TM emulators. Under 2.9 and 4.3, 060000 is stuffed into tmcs for 800BPI (which puts a standard DEC TM into 800BPI 9-track mode), and a 0 is used for 1600BPI. (4.3 uses a 020000 for 6250BPI for the AVIV.) I'm trying to get the 2.10BSD stand alone boot fixed up with better support for 1600BPI - our only distribution density. Will I get in trouble if I have the stand alone primary boot stuff a zero into tmcs? This would cause a DEC TM to go into 7-track ???BPI, but then a DEC TM wouldn't be able to read in the primary bootstrap in any case ... As I understand it, most TM emulators ignore the 060000 bits in tmcs entirely and use a physical switch on the drive to select density. Casey