[Simh] Subject: Re: something strange with simulated RK05 drive ?

[Bob Supnik]

To my surprise, format is actually mechanized in the RK11 simulator. 
Whether it's mechanized correctly is another story, of course.

There are only two tests for the format bit.

1. If FORMAT is set when GO is set, and the command is anything other 
than READ or WRITE, then PGE (programming error)
     is set, and the operation terminates. (See the RKER register 
description.)
2. If FORMAT is set during READ, one header word is transferred from 
consecutive sectors to fill the buffer.

According to the maintenance course, the header is just the cylinder 
address, positioned as in RKDA.

Write + Format is the same as write, except that the header is not 
checked for being on the correct cylinder before writing the sector. 
Normal writing always rewrites the header word. So a "real" format 
program can write a bad drive, with incorrect headers. The simulator can't.

Personally, I've never tried RT-11 FORMAT, and I sort of feel this way 
about it:

Patient: "It hurts when I do that!"
Doctor: "Don't do that."

However, if someone has RT11 source code and wants to trace what's going 
on, I can dig deeper.

/Bob