>Would you explain what a "unit" represents?  All the schools I've gone
>to have equated a unit with approximately one hour of in-class time
>per week.  Typically a graduate class or TA responsibility was 3 units
>and a full-time graduate student took 9 units.  So, I'm not sure what
>36 CMU units means as a workload.

I know this is a confusing number system ...

At CMU a minimum load for a full-time student is 36 units.  At the undergrad
level each 3 units are roughly equivalent to one hour of in-class time per
week.  But you will find that most grad classes (and the more "difficult"
undergrad classes) are 12 units for three hours of meeting time per week.
The extra 3 units is because more out-of-class time is expected than for
undergrads (== the work is harder).  

Of course, none of this holds in the fall semester for the CS core courses 
-- which meet for 4-1/2 hours per week -- that's because we have to make up 
for the three weeks spent in the IC.

In general, the rule is that you shouldn't worry about units at all.  We only
have them because the university says we must -- and we don't track the number
of units any student takes, other than to make sure everyone is registered
full-time.  The only thing we track is the number of core-units passed -- and
once you have 8, that's it.  It doesn't really matter how many units, what
order they are taken, etc....