Issue No. 03 - May/June (1973 vol. 6)
The ISP (for Instruction Set Processor) notation was developed for a text [Bell& Newell, 1971] to precisely describe the programming level of a computer in terms of its Memory, Instruction Format, Data Types, Data Operations, Interpreting a Specific Instruction Set.
C.G. Bell, D. Siewiorek, M. Barbacci, "ISP: A Notation to Describe A Computer's Instruction Sets", Computer, vol. 6, no. , pp. 22-24, May/June 1973, doi:10.1109/C-M.1973.217035