[Simh] Bad blocks

[Bob Supnik]

On the PDP11 and VAX, RL, RP, and RM drives require bad block formatting 
after an initial attach (that is, creation of a new file). After that, 
the question should not be asked again.

The PDP10 operating systems did their own bad block management and did 
not require a standard bad block table.

The relevant DEC standard, 144, is here: 
http://bitsavers.trailing-edge.com/pdf/dec/standards/EL-00144_B_DEC_STD_144_Disk_Standard_for_Recording_and_Handling_Bad_Sectors_Nov76.pdf

/Bob