Calling something an apparatus vs a machine or a system doesn’t change the scope of a claim.
We usually use system when a machine is defined by the actions it takes when engaged.
If a physical thing performs the actions a claim uses to define a system, it infringes. An infringer saying it’s not a system it’s an apparatus doesn’t change that.
The statutory categories are process, machine, article of manufacture, composition of matter and improvements to them.
Compositions of matter, machines and articles of manufactures are physical things. Processes are steps of action.
Thing or action is a big difference. Among the “things”, composition of matter is very different than other things in that it has no shape or parts - like a bucket of adhesive or paint or fertilizer.
Machines and articles of manufacture are both things with distinct physical features and functions. A floppy disk with bits encoded magnetically is an article of manufacture as is a car which is also a machine.
The distinction between those two categories is not a bright line and also not usually important.
These statutory divisions were created hundreds of years ago. Now we use words like device and apparatus. They are patentable subject matter by falling into either of the physical categories other than composition of matter.
Informally, I guess an apparatus is a relatively small machine or article of manufacture and usually defined by the interrelation of physical components.
A mechanical machine could be defined by its actions, like a typical system claim, or by the physical structure and interactions of its gears, etc. Either is a machine but you might call the gear by gear definition an apparatus. Calling it an apparatus vs a system isn’t important but defining the machine in a different way would be important.
Most modern systems can’t be defined in a gear by gear by spring manner.
