The critical path is a key concept in the design of the `Memory Pool
System /project/mps/ Code on the critical
path is usually executed more than any other code in the process.  A
change of just one instruction on the critical path can make as much as
a 1% difference in overall run-time.  A lot of the design of the MPS is
arranged around making the critical path as short and fast as possible.
This document describes the critical path and explains some of that
design, with reference to more detailed documents