Requirements Document vs Design Input/Outputs vs SRS


Hi, I've got an issue with how design documents are referred to between purely mechanical devices and those that include software. I'm trying to get a clear answer on which documents contain what information.
In a purely mechanical device (e.g. a device that deploys stents, or an IV bag) I would normally expect a User Needs document, and a Design Inputs/Outputs document where the device requirements are the design inputs and the specifications (e.g. Diam 0.5+-0.15) are the outputs. Note: Yes, I am very much aware that people will often list drawings that contain the specification rather than the individual spec itself, and thats fine as long as its understood that testing should confirm that the spec (output) satisfies the requirement (input), and not that the drawing has the spec on it. However, I get turned around when it comes to software. I keep trying to understand what an example of a software requirement is and what a resultant software specification might be. And I can't find a direct and clear answer, especially not with a document called the software requirements specification (srs). Everything online tells me that the srs contains the software requirements, and so I mentally read the srs acronym instead as software requirements document for personal clarification. But then I am left wondering, where then are the specs kept?
I come from a mechanical engineering background and have low to moderate understanding of software. A lot of the time in the industry people don't know the difference between a requirement and a spec and use them interchangeably, which drives me insane. So can someone please try to clear this up for me? I'm starting to think that software documentation just has requirements and not specifications, or rather the "spec" is just the code itself.


Super Moderator
You could have software specs for aspects like algorithm descriptions & GUIs (there may be more).

Software is intended to drive mechanical folks insane. :)


Trusted Information Resource
In both hardware and software: A requirement can be satisfied by any number of possible specifications.

Mechanically: The requirement may be to have something like a transmission ratio of 2:1, the specification might be the number of teeth on each gear.

Software: The specification may be to "sort a list", the specification could be what kind of algorithm.
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