The short answer
RAM stands for Reliability, Availability and Maintainability — how much of the time a system performs its function, and how failures and repairs drive that. RAMS adds a fourth letter, Safety: not just “will it produce?” but “how likely is a dangerousfailure, and is that risk tolerable?”
They share methods and data, but answer different questions and are held to different standards. A study can be one, the other, or both — so it is worth being explicit about which you mean.
What RAM covers
A RAM study is about production and uptime: availability targets, redundancy and standby, maintenance strategy, spares, and the throughput a system delivers over its life. The headline output is an availability or production-availability figure, with the equipment that drives downtime ranked behind it.
The methods are reliability block diagrams, Monte Carlo simulation, failure/repair data and importance analysis. Common references include IEC 61078 (RBDs), ISO 20815 (production assurance) and ISO 14224 (equipment data).
The extra “S” — Safety
The Safety leg of RAMS asks a fundamentally different question: not how much the system produces, but how likely it is to fail dangerously, and whether that probability meets a tolerable-risk target. That brings in hazard analysis, safety functions and integrity levels (SIL), with their own quantitative targets such as probability of failure on demand.
Safety work is governed by a separate family of standards — IEC 61508 (functional safety), IEC 61511 (process-industry safety) and, in rail, the EN 50126series that actually defines the term “RAMS”. These overlap with RAM in the data and some techniques (fault trees, FMEA) but are a distinct discipline with distinct deliverables.
Side by side
| RAM | The Safety leg of RAMS | |
|---|---|---|
| Core question | How much of the time does it produce / function? | How likely is a dangerous failure, and is the risk tolerable? |
| Typical output | Availability, production availability, loss contributors | SIL, probability of failure on demand, risk reduction |
| Methods | RBD — by Monte Carlo simulation or exact analytical (Markov); importance, sensitivity | Hazard analysis, fault trees, SIL verification |
| Key standards | IEC 61078, ISO 20815, ISO 14224 | IEC 61508, IEC 61511, EN 50126/50129 |
In practice the two inform each other — the same equipment failure data feeds both — but a production-availability study and a SIL verification are different pieces of work.
Where Ramly fits
Ramly is a RAMtool. It models systems as reliability block diagrams and runs Monte Carlo simulations to predict availability, production and downtime cost. It is built for the “will it produce, and where is the downtime?” question.
It does not perform the Safety leg — there is no SIL verification, probability-of-failure-on-demand calculation or hazard analysis. If your scope is functional safety, that is a different tool and a different standard. If your scope is availability and production, that is exactly what Ramly does.
Run a RAM study in the browser
Open a worked example model and see the availability, throughput and loss-contributor results for yourself.