=head1 TITLE

The Design Of MIX simulator and its assembler

=head1 REQUIREMENT


=head1 IO System

The IO devices of MIX is 60s era. 

Fortunately, we only have to know how they function with the MIX core.
We know that each io device has a unit number, and has a flat storage.
The device also has to maintain the ready bit.
Some device can tell when the current activity will end.
But some not. For example, if the card reader is waiting for card, 
or reading the teletype client.

when simulation began, it is assumed that all cards should be already 
correctly handed in.

Hand a card deck in, so the other day you will get some result.

We have to understand how the programmers ran programs in the 1960s.
They could not have their own. When they wrote program on cards,
they hand the card deck to a operator. ANd the operator will then
run the program for them, and report the result.

   So device has some common interfaces.
