DeveloperCarnegie-Mellon University
Written inBLISS
OS familyCapability-based
Working stateDiscontinued
Initial release1971; 53 years ago (1971)
Final releaseFinal / 1975; 49 years ago (1975)
Marketing targetResearch
Available inEnglish
Update methodCompile from source code
Kernel typeMicrokernel
user interface
Command-line interface

Hydra (stylized as HYDRA) is an early, discontinued, capability-based, object-oriented microkernel designed to support a wide range of possible operating systems to run on it.[1] Hydra was created as part of the C.mmp project at Carnegie-Mellon University in 1971.[2]

The name is based on the ancient Greek mythological creature the hydra.

Hydra was designed to be modular and secure, and intended to be flexible enough for easy experimentation.[3] The system was implemented in the programming language BLISS.[4]


  1. ^ Wulf 74 pp. 337–345
  2. ^ Siewiorek, Daniel P.; Bell, C. Gordon; Newell, Allen; Mashburn, Henry M. (1982). Computer Structures: Principles and Examples. New York, New York: McGraw-Hill.
  3. ^ Levy, Henry M. (1984). Capability-Based Computer Systems (PDF). Digital Press.
  4. ^ Wulf, William A.; Harbison, Samual P. Reflections in a pool of processors: An experience report on C.mmp/Hydra (PDF) (Report). p. 945.