The Free On-line Dictionary of Computing (30 December 2018):
(IT) An early compiler for
mathematics developed by A.J. Perlis et al at Carnegie Tech
ca 1957. IT was originally written for the Burroughs 205,
then the IBM 650.
IT was the forerunner of RUNCIBLE, GATE, CORRELATE and GAT.
IT source code was converted to PIT, thence to SPIT.
IT-2 produced machine language directly, IT-3 developed at
Carnegie added double-precision floating-point.
[Sammet 1969, pp. 139-141].
[CACM 1(5):22 1958].