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A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11The system development life cycle is the full span of work involved in bringing a system into use, operating and maintaining it, and eventually retiring it. It covers more than coding: a common NIST model includes initiation, development or acquisition, implementation and assessment, operations and maintenance, and disposal. The acronym SDLC can also mean software development life cycle, so the intended scope matters.
What does the system development life cycle mean?
NIST defines the system development life cycle as the activities associated with a system, from initiation through development and acquisition, implementation, operation and maintenance, and ultimately disposal. In other words, the lifecycle follows the system from the decision to create or obtain it through its useful life and retirement. See the NIST glossary definition.
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A related term, system life cycle, describes the period from conception until the system is destroyed or no longer available for use. In practice, it is often used synonymously with SDLC; NIST’s system life cycle glossary entry gives that framing.
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SDLC is used for both “system development life cycle” and “software development life cycle.” NIST’s software-specific definition describes a formal or informal methodology for designing, creating and maintaining software, including code built into hardware. The broader system lifecycle also encompasses such work as acquiring a system, putting it into service, maintaining it in operation and retiring it. See NIST’s software development life cycle definition.
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What are the five common system life cycle phases?
NIST Special Publication 800-64 Revision 2 presents a typical five-phase model. The phases are broad activities, not a universal checklist that every organization must follow in exactly the same way.
- Initiation: Establish the need for a system, define its purpose and begin planning. This is also when the organization starts identifying information and security requirements.
- Development or acquisition: Design and build the system, program it, purchase it or otherwise obtain it. The appropriate route depends on what the organization needs and its acquisition approach.
- Implementation and assessment: Test and assess the system, then install or field it for use. Assessment is part of preparing the system for deployment, not simply a coding activity.
- Operations and maintenance: Run the system to perform its intended work and maintain it while it remains in service.
- Disposal: Retire the system when it is no longer needed, accounting for the transition away from it.
This phase framing comes from NIST SP 800-64 Revision 2. It is a useful overview; organizations can use different phase names, divide activities differently or repeat work before disposal.
Is the system development cycle always a fixed sequence?
No. A lifecycle model describes how work is organized, and different models arrange sequence, feedback and iteration differently. NIST discusses traditional linear sequential (Waterfall), prototyping, rapid application development, joint application development and spiral approaches in its NISTIR 7499. The five phases above should therefore be understood as a high-level lifecycle, not a claim that every project passes through five one-time gates in order.
Model selection can depend on the system’s expected size and complexity, development schedule and expected life. Organizational acquisition policy may also constrain the available approach. When assessing a model, consider how it handles changing requirements, iteration, assessment and security, as well as those project and policy constraints.
How does security fit into the lifecycle?
Security planning should start early and continue through the system’s life rather than being left until implementation. NIST’s lifecycle guidance calls for identifying information and security requirements during initiation, then carrying out security work appropriate to development or acquisition, assessment, operations, maintenance and disposal. The precise tasks vary by system, but protection needs and risks are lifecycle concerns at every phase. See NIST SP 800-64 Revision 2.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why does the definition matter?
Calling the lifecycle “system development” can make it sound as though the work ends when a product is built. The broader definition makes clear that obtaining, deploying, operating, maintaining and retiring the system are also part of its life. When discussing SDLC, specify whether you mean the whole system lifecycle or a software-focused development method; that distinction prevents a narrow coding process from being mistaken for the full management of a system.
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