I quite often come across this question in my requirements engineering and business analysis workshops - How are System Requirements Specifications different from Software Requirements Specifications?
As we have shown in the above image, the system is a broader concept than software. Systems usually comprise 4 key elements - People, Process, Technology, and Partners. So when we are considering system requirements, we need to consider requirements from all 4 broad aspects i.e. People, Process, Technology, and Partners.
People requirements may require aspects related to capabilities and motivation. Without the right capabilities and motivation, no project is going to be successful.
Process requirements may require processes to be re-engineered to make them more effective.
Partner requirements may require an organization to look for partners who can support current and future business needs.
Technology requirements can be primarily related to information technology or technologies which are becoming useful to businesses such as clean energy, nanotechnology etc.
Information Technology requirements, in turn, contain aspects such as Hardware, Software, and network requirements.
Hardware requirements require specifications on the processor, RAM, memory etc.
Network requirements may require specific bandwidth expectations.
Software requirements usually contain requirements with respect to functionalities provided by the system and expectations on non-functional aspects of the solution such as performance, security, and scalability etc.
However, in many instances, the hardware and network may not be affected by the project and only software is affected.
For example, we may add a new feature to an existing software solution. It may so happen that we do not affect people, processes or partners. In such a case, technology requirements equal software requirements, and system requirements equal software requirements.
However, for larger changes, typically software requirements will be the subset of system requirements.
We should use SRS to indicate Software Requirements Specifications and SyRS to indicate System Requirements Specifications.