PACT was a series of compilers for the IBM 701 and IBM 704 scientific computers.
Their development was conducted jointly by IBM and a committee of customers starting in 1954.
PACT I was developed for the 701, and PACT IA for the 704.
The emphasis in that early generation of compilers was minimization of the memory footprint, because memory was a very expensive resource at the time.
[1] The word "compiler" was not in widespread use at the time, so most of the 1956 papers described it as an "(automatic) coding system",[2][3] although the word compiler was also used in some papers.