# General Purpose Simulation System (GPSS) GPSS is one of the earliest simulation languages, first released by Geoffrey Gordon at IBM in 1961. It is a transaction-oriented [[Discrete-Event Simulation (DES)]] language in which a model is expressed as a block diagram: transactions (tokens representing customers, jobs, or messages) flow through a fixed graph of blocks (queues, servers, delays, assignments), and their progress drives the simulation clock forward. Gordon had built message-switching simulations at Bell Labs in the late 1950s. At IBM he generalised that work into a reusable block-diagram language, first called the Sequence Diagram Simulator and later the "Gordon Simulator" before being officially released as GPSS I on 27 September 1961, with 25 block types running on the IBM 704. Later versions (GPSS II, III, 360, V, World) ran on progressively newer IBM hardware, and dialects such as GPSS/H and GPSS World remain in use today, particularly in teaching. GPSS matters historically because it established the transaction-flow paradigm that still dominates commercial DES tools such as AnyLogic, Arena, and ProModel. It was one of the first domain-specific languages for any application area, and its sixty-plus-year lifespan is among the longest of any programming language. # References - [GPSS (Wikipedia)](https://en.wikipedia.org/wiki/GPSS) - [Geoffrey Gordon — Computer Pioneers](https://history.computer.org/pioneers/gordon.html) - [The development of the General Purpose Simulation System (Gordon, HOPL 1978)](https://dl.acm.org/doi/10.1145/800025.1198386)