Software in a Medical Device (SiMD)

Medical device software plays a critical role in product safety, performance, and regulatory compliance. Manufacturers must manage software risks, validation, documentation, cybersecurity, and changes throughout the device lifecycle while meeting applicable FDA requirements and industry standards. 

What Is Software in a Medical Device (SiMD)?

Software in a Medical Device (SiMD) refers to software that is built into, and operates as an integral part of, a physical medical device's hardware. Unlike standalone software that runs independently on a computer or mobile phone, SiMD only exists and functions as part of the device it's embedded in, it has no purpose or use outside of that hardware.

SiMD's role within a device can be diagnostic (interpreting a signal to support a diagnosis), monitoring (tracking a physiological parameter over time), therapeutic (actively delivering a treatment, as with the insulin pump), or control-related (directing the mechanical or electronic operation of the device). Not all embedded software automatically counts as regulated medical-device software, what matters is the software's intended function. 

How Does Software in a Medical Device Work?

SiMD operates through a defined sequence that runs from data input to device output, generally following this process:

• The device collects input from sensors, users, or connected systems — for example, a glucose sensor reading, a button press, or a signal from another connected device.
• The software processes the data, converting raw sensor or input signals into a form the device's logic can work with.
• The software applies programmed logic or algorithms to determine the appropriate response — a calculation, a classification, or a control decision.
• It generates an output or controls the hardware, such as triggering a pump mechanism, displaying a reading, or adjusting a device parameter.
• It monitors performance and identifies errors, continuously checking that the device and software are operating within expected parameters.
• It activates alarms or a safe-state response when necessary, alerting the user or shutting the device into a safe operating mode if something falls outside acceptable limits.

Common Examples of SiMD Software

• ECG device software — processes electrical signal data from electrodes and generates the waveform and readings a clinician interprets.
• Imaging-system acquisition software — controls how an imaging device (such as an X-ray or ultrasound unit) captures and constructs an image.
• Surgical-robot control software — translates a surgeon's input into precise, controlled movement of robotic surgical instruments.
• Dialysis-machine control software — manages fluid flow rates, filtration parameters, and safety interlocks during treatment.
• Alarm-management software inside a device — monitors device sensors and triggers audible or visual alerts when a parameter falls outside a safe range.
• Infusion pump dosing software — calculates and controls the rate and volume of fluid or medication delivered to a patient.
• Ventilator control software — regulates breathing cycle timing, pressure, and volume delivered to the patient.
• Patient monitor software — aggregates vital-sign data from multiple sensors and displays it in real time at the bedside.
• Implantable pacemaker software — controls the timing and delivery of electrical pulses to regulate heart rhythm.
• Laboratory analyzer control software — manages sample processing and instrument operation within a diagnostic lab device.

SaMD vs. SiMD in the same clinical area: The same clinical function can involve either SaMD or SiMD, depending on how the software is deployed. Software embedded in an imaging system to control image capture is SiMD, it exists only as part of that hardware. A separate application that independently analyzes the resulting image, running on a general-purpose computer, for instance, without controlling the imaging hardware itself, may be SaMD instead. The distinction isn't the clinical task; it's whether the software is inseparable from a specific piece of hardware or capable of functioning independently.

SaMD vs. SiMD: What Is the Difference?

Software as a Medical Device (SaMD) and Software in a Medical Device (SiMD) are often confused because both involve medical software, but the distinction between them shapes everything from how they're built to how they're regulated. The core difference comes down to hardware dependency: SaMD runs independently of any specific medical hardware, while SiMD is embedded in, and inseparable from, a physical device.

	SaMD	SiMD
Full form	Software as a Medical Device	Software in a Medical Device
Hardware dependency	Runs on general-purpose computing platforms (PCs, mobile devices); not tied to specific medical hardware	Embedded in and inseparable from a specific medical device's hardware
Product type	Standalone software product	Component of a hardware medical device
Example	A mobile app that analyzes medical images to detect abnormalities	Software embedded in an imaging device that controls image capture
Regulatory boundary / requirements	Regulated as the medical device itself; evaluated independently under frameworks like FDA's SaMD pathways or IMDRF risk categories	Regulated as part of the overall device submission; software documentation is one component of the device's premarket submission
Testing focus	Software verification and validation as the primary basis for safety and effectiveness	Software verification and validation alongside hardware-software interface testing and full device-level validation
Risk approach	IMDRF SaMD risk categorization (Category I–IV) based on the significance of information provided and the healthcare situation	Risk assessed as part of the device's overall risk management file, informed by IEC 62304 software safety classification
Change impact	A software update can be released and evaluated largely on its own	A software change may require re-evaluating the entire device, since the software and hardware function as one system
Submission scope	The submission is built around the software itself	The submission covers the complete device, with software documentation as one required component

How Is SiMD Classified as Part of a Medical Device?

Classifying SiMD isn't a separate exercise from classifying the device it's part of. The software is evaluated as a component of the device's overall risk profile. The classification of SiMD depends on the medical device's intended use, its risk level, the specific function the software performs, and the potential harm that could result if the software fails.

Main classification factors include the FDA device class the overall device falls into (Class I, II, or III), the specific product code assigned to the device type, and the regulatory submission pathway that applies, such as 510(k) clearance, De Novo classification, or Premarket Approval (PMA). Each of these factors influences how much software documentation a submission needs to include.

Relevant FDA guidance: The FDA's guidance document Content of Premarket Submissions for Device Software Functions (finalized June 14, 2023) governs how software documentation should be prepared and evaluated for premarket submissions that include a device software function. This guidance replaced the FDA's earlier "Level of Concern" framework, which had classified software as Minor, Moderate, or Major.

Basic and Enhanced Documentation Levels: Under the current guidance, the FDA uses a risk-based approach that sorts submissions into one of two Documentation Levels (Basic or Enhanced), rather than the previous three-tier system. Basic Documentation applies to software where a failure would not be expected to result in a hazardous situation with a probable risk of death or serious injury.

An important clarification: FDA device class (I, II, III) reflects the overall device's regulatory risk category. IEC 62304 software safety classification (A, B, C) reflects the potential for the software itself to contribute to a hazardous situation, independent of the device's regulatory pathway. IMDRF SaMD risk categories (I–IV) apply specifically to standalone SaMD products, based on the significance of the information the software provides and the state of the healthcare situation.

What Are the Key Risks and Regulatory Considerations for SiMD?

SiMD risk matters in a way that's distinct from ordinary software risk: because the software is embedded directly in a physical device, a software failure can directly affect the device's mechanical or electronic behavior, and, in turn, patient safety, in ways that standalone software failures typically cannot.

Functional and safety risk. A software defect in SiMD can cause the device to behave incorrectly — delivering an incorrect dose, misreading a sensor, or failing to trigger a needed alarm. Because the software directly controls physical device behavior, these failures translate immediately into a physical safety event rather than remaining a data or display error.

Cybersecurity risk. Connected and embedded devices are increasingly exposed to cybersecurity threats that can compromise device functionality, not just data confidentiality. FDA's current guidance explicitly considers whether device functionality could be intentionally or unintentionally compromised through inadequate cybersecurity controls, and expects that risk to be evaluated alongside conventional software hazards.

Change management risk. Because SiMD is inseparable from its hardware, even a small software update can require re-verifying the entire device, including the hardware-software interface, rather than being evaluated as an isolated software release. Poorly managed change control is a common source of downstream compliance and safety issues.

Verification and validation gaps. Incomplete testing of the hardware-software interface, or validation performed only on the software in isolation rather than the complete device in representative conditions, is a recurring source of risk that regulators scrutinize closely during premarket review and post-market surveillance.

Documentation and traceability risk. Because Documentation Level determinations, risk management files, and design history records must all align, gaps in traceability between requirements, identified hazards, and verification/validation evidence create regulatory risk even when the software itself performs correctly.

Related Terms

• Software as a Medical Device (SaMD)

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