The goal of the implementation phase is to implement a system correctly, efficiently, and quickly on a particular set or range of computers, using particular tools and programming languages. The implementation stage is primarily environmental and works with the realities of particular machines, system, language compilers, tools, developers, and clients necessary to translate a design into working code. Just as the design phase may include some analysis efforts approached from a computational standpoint, the implementation phase essentially always includes design efforts. Implementation level design is a reconciliation activity, where in principle executable models, implementation languages and tools, performance requirements, and delivery schedules must finally be combined. All while maintaining correctness, reliability, extensibility, maintainability and related criteria. .
The first stage of implementation includes many activities. Coding is the first activity. The software developers take the design documents and development tools such as editors, compilers, and debuggers and then start writing software. This is usually the longest phase in the product life cycle. Each developer has to write their own code and collaborate with other developers to make sure that different components can interoperate with each other. In large and complex projects, someone also needs to decide directory hierarchy so that files are stored in appropriate locations. During the development cycle, multiple persons may modify files. If everyone is not following the rules then this may easily break the whole compilation and building process. Writing good comments is very important as all other documents will be lost eventually. .
The next is testing. System testing involves testing hardware devices, testing and debugging computer programs, and testing information processing procedures. Programs are tested using data that attempt to simulate all conditions that may arise during processing.