APA (7th ed.) Citation

Peterson, J. L., Norman, T. A., & Gaines, R. S. (1977). Buddy System. Communications of the ACM, 20(6), 421. https://doi.org/10.1145/359605.359626

Chicago Style (17th ed.) Citation

Peterson, James L., Theodore A. Norman, and R. S. Gaines. "Buddy System." Communications of the ACM 20, no. 6 (1977): 421. https://doi.org/10.1145/359605.359626.

MLA (9th ed.) Citation

Peterson, James L., et al. "Buddy System." Communications of the ACM, vol. 20, no. 6, 1977, p. 421, https://doi.org/10.1145/359605.359626.