OT Asset Inventory vs OT Asset Discovery

Operational technology (OT) environments depend on a wide range of devices, systems, and software working together reliably. Knowing what is present in those environments is a prerequisite for security, resilience, and safe operation.

Two related terms are often used interchangeably: OT asset inventory and OT asset discovery. They are closely linked, but they are not the same thing. In real OT environments, treating them as equivalent often leads to gaps in visibility and misplaced confidence.

Here we explain the difference between the two, why the distinction matters, and how each concept fits into operational settings.

Discovery is a process; inventory is an output

OT asset discovery is an ongoing process.

OT asset inventory is a snapshot produced by that process.

Asset discovery refers to the methods used to identify what exists in an OT environment. This can include:

• passively observing network traffic
• identifying devices communicating on industrial protocols
• detecting firmware versions, operating systems, and configurations
• spotting changes over time, such as new or removed assets

An asset inventory is the result. It is typically a list or database that records:

• device names or identifiers
• asset types (PLC, HMI, historian, sensor)
• network locations
• vendor and model information
• ownership or responsibility

In practice, discovery answers the question “what is actually happening on the network?”

Inventory answers “what do we believe exists right now?”

This distinction matters because inventories do not maintain themselves, a point that is frequently underestimated in operational settings.

Why static inventories fail in OT environments

Many OT asset inventories are created manually. Common sources include:

• spreadsheets maintained by engineering teams
• commissioning documentation from system integrators
• records created during audits or compliance exercises

These approaches often fail over time for several reasons.

First, OT environments tend to change incrementally. Devices are replaced during maintenance, temporary systems remain in place, and access solutions are added to solve immediate operational needs. Over time, these small changes accumulate.

Second, updates are not always recorded. It is common to see inventories lag behind reality when documentation is treated as a secondary task during maintenance or fault resolution.

Third, modern OT environments are increasingly interconnected. Industrial systems now interact with IT networks, cloud platforms, and third-party services. As connectivity grows, manually maintained inventories struggle to reflect the true scope of what is connected.

As a result, a static inventory can appear complete while gradually diverging from the live environment.

How inventories decay without monitoring

Asset inventories begin to lose accuracy as soon as they are created.

This decay typically shows up as:

• devices remaining listed after being decommissioned
• firmware and software versions becoming outdated
• network paths changing without being reflected
• previously unknown assets appearing without notice

In operational environments, this pattern is common where inventories are only reviewed periodically. Without continuous discovery or monitoring, there is little visibility into when the documented view stops matching reality.

In OT environments, this matters because inaccurate asset records can:

• obscure unmanaged access paths
• slow down incident response
• complicate safety and availability assessments
• weaken the quality of risk and compliance decisions

Where inventories still add value

Despite their limitations, OT asset inventories remain important.

Inventories are particularly useful for:

• establishing an initial baseline view
• supporting governance and regulatory requirements
• clarifying ownership and accountability
• planning maintenance, upgrades, or system changes
• providing a shared reference across engineering, IT, and management teams

In many environments, inventories function as a coordination tool rather than a source of real-time truth. Used with this understanding, they continue to play a valuable role.

How discovery and inventory work together

In more mature OT environments, asset discovery and asset inventory are treated as complementary rather than interchangeable.

Discovery provides ongoing visibility into what is present and how it behaves.
Inventory provides a structured record that can be reviewed, governed, and communicated.

Where discovery informs inventory, changes are identified rather than assumed, and records stay closer to operational reality.

Understanding this relationship helps avoid a common pitfall: assuming that a static inventory equates to visibility.

In OT environments, visibility is not a document. It is an ongoing activity, supported by records that are kept aligned with how systems actually operate.

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