---
title: "Define system, model, simulation"
subject: "Simulation and Modeling"
chapter: 1
key: "semester_8/simulation_and_modeling:system-model-simulation-define"
source: https://www.bctengineer.com/q/semester_8/simulation_and_modeling/system-model-simulation-define
site: BCT Engineering
---

# Define system, model, simulation

Simulation and Modeling · Chapter 1: Introduction to Simulation

- Asked in: 2073 Magh, 3+1+4 marks
- Video: [Modeling & Simulation 101](https://www.youtube.com/watch?v=X-6zxImekOE) — IITSEC
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/simulation_and_modeling/system-model-simulation-define
- Whole chapter: https://www.bctengineer.com/md/semester_8/simulation_and_modeling/chapter-1

## Question

Define system, model and simulation, and clarify with a suitable example. List various advantages and disadvantages of simulation.

## Short answer

A system is a set of interacting entities (e.g., bank customers and tellers). A model is a simplified representation of that system, such as a queue model. Simulation is the imitation of its operation over time to evaluate performance. Advantages: safe experimentation, time compression, handling complexity. Disadvantages: need for training, random output, cost, and possible misuse.

## Answer

#### Definitions
- **System:** a collection of entities that act and interact together to achieve some logical end. Example: a hospital outpatient department with patients, doctors, nurses and rooms.
- **Model:** a representation of a system, usually simpler than the system, used to study it. It keeps the aspects that matter for the purpose of the study and leaves out the rest. Example: a queue with one arrival stream and several servers that represents the outpatient department.
- **Simulation:** the imitation of the operation of a real system over time by experimenting with its model. Example: running the queue model on a computer for a simulated month, with random patient arrivals and service times, and recording the average waiting time.

#### Example
A bank has two tellers. System: customers, tellers, queue. Model: arrivals are random with a mean gap of 2 minutes, service takes about 3 minutes, and one queue feeds two tellers. Simulation: generate arrival and service times, step the clock through events, and measure average waiting time and teller utilization. The bank can then see the effect of a third teller before hiring one.

#### Advantages of simulation
- Tests changes without disturbing the real system.
- Time can be compressed or expanded.
- Gives insight into interactions and bottlenecks.
- Works for complex stochastic systems with no analytical solution.
- Cheaper and safer than real experiments; good for training.

#### Disadvantages of simulation
- Needs special training to build a good model.
- Output is random and can be difficult to interpret.
- Can be costly and slow to develop and run.
- May be used when a simple analytical solution is available.
- Results are only as good as the model and its data.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. A model of a system is best described as:
   A. An exact copy that keeps every detail
   B. A representation, usually simpler, that keeps the aspects that matter for the study
   C. The imitation of the system over time
   D. The environment outside the system
   Answer: B. A model is a simpler representation keeping only what matters for the purpose of the study. (Key point: Definition of model)

2. In the bank example, running the queue model with random arrivals and service times and measuring average waiting time is the:
   A. System
   B. Model
   C. Simulation
   D. Environment
   Answer: C. Simulation is experimenting with the model over time; the system is the bank and the model is the queue description. (Key point: Simulation vs model)

3. What decision can the bank simulation support?
   A. Who the customers are
   B. How to reduce randomness in arrivals
   C. How to avoid collecting any data
   D. The effect of adding a third teller before hiring one
   Answer: D. The simulation shows effects like waiting time and utilization with a third teller without changing the real bank. (Key point: Use of simulation in bank)

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