Ask any simulation engineer about their first project, and many will mention waiting lines (queues). Gordon’s treatment of single-server and multi-server queues remains the gold standard. Why? Because the core challenges haven’t changed:
Gordon’s GPSS block diagrams—those deceptively simple boxes and arrows—taught a generation to think in events, not seconds.
Even today’s tools (AnyLogic, Simio, Python’s SimPy) inherit Gordon’s conceptual DNA. When you declare a Resource or Process in modern code, you’re speaking a dialect he helped invent.
Let’s translate a classic Gordon problem (A single-server queue) into modern Python using SimPy, showing why the PDF is still useful.
Gordon’s GPSS logic:
GENERATE 10,5 ; Customers arrive every 10±5 min
QUEUE LINE ; Enter the waiting line
SEIZE TELLER ; Take the teller if free
DEPART LINE ; Leave the line
ADVANCE 12,4 ; Service takes 12±4 min
RELEASE TELLER ; Free the teller
TERMINATE ; Customer leaves
Modern Python (SimPy):
import simpy import randomdef customer(env, name, server): print(f'name arrives at env.now:.2f') with server.request() as req: yield req # This is the SEIZE (and implicit QUEUE) print(f'name starts service at env.now:.2f') service_time = random.uniform(8, 16) # ADVANCE 12,4 range yield env.timeout(service_time) print(f'name leaves at env.now:.2f') # RELEASE
env = simpy.Environment() server = simpy.Resource(env, capacity=1) for i in range(10): env.process(customer(env, f'Customer i', server)) yield env.timeout(random.expovariate(0.1)) # GENERATE
env.run()
If you understand Gordon’s GPSS block diagram, you can write SimPy code in your sleep. That is the power of the "System Simulation" foundation.
For decades, one book has quietly shaped how engineers, economists, and computer scientists predict the future—without a crystal ball.
In the late 1960s, most people thought of computers as number-crunchers for payroll or ballistic trajectories. But Geoffrey Gordon, a researcher at IBM’s Thomas J. Watson Research Center, saw something else: a mirror.
His 1969 textbook, System Simulation, didn’t just teach programming. It introduced a radical idea—that you could build a virtual twin of a real system, tweak its inputs, and watch time unfold at warp speed. Today, that discipline is called discrete-event simulation. Back then, it was Gordon’s quiet revolution.
