Something can be obsolete AND still in use. The T-72 and T-80 both see widespread use, but are both obsolete. 😉
Yeah, I was wondering how I would explain the word obsolete to a child, and it's a bit complicated provided that there is still a sensible use for it. I think there are several factors to consider before labelling something as obsolete.
Example: A relative gave me a nice pen for my 21st birthday.
Reasons to consider it obsolete:
1 - Better alternatives are available (ie. methods for storing information)
2 - It's probably no longer in production.
Reasons for it not to be considered obsolete:
1 - Consumables for it are still in production / available to buy.
2 - It does its job as well as it did on day one.
3 - It performs certain functions more conveniently than other methods of storing information.
I suppose a particular typewriter could be considered obsolete given similar arguments but simply because consumables aren't available for it any more. However, a typewriter has one or two advantages over newer alternatives depending on who is meant to use it.
I suppose a quill and ink pot should be considered obsolete because even though consumables are readily available, there are better alternatives available and it no longer does anything better than the alternatives.
Considering Windows 7 as obsolete is like saying a model 2013 car is obsolete because a model 2014 car is available. The latter may have improved xyz, but that's about it. Windows 7 is even still available to buy new (legitimately)!
I suppose I might consider the word obsolete to also mean that there are serious obstacles in the way of using a particular item and there are (all round) better, newer alternatives available. 'Almost useless', perhaps.