Your laptop's SSD sure, 2GB/s - that 5400 rpm laptop hard disk that your user has is writing at a measly 1mb/s because the disk is also being accessed by 5 other programs.
Now the user is either queuing up a bunch of background saves leading to overload or is forced to wait 1s per keystroke.
Well done!
I guess the simple solution then is to tell the user to buy a $3000 laptop just so it's capable of running notepad.
Hmm...Mac laptops have been SSD-only for how many years?
Anyway, even laptop drives are well over 40-50 MB/s these days, and any disk scheduler worth its salt will schedule this kind of write (one contiguous chunk) near optimally, so still 40-50 writes/s.
And of course, you queue these writes asynchronously, dropping as needed, so if you actually manage to out-type your disk, all that happens is that your save-rate drops to every couple of characters. Big whoop.
Also remember that this is Moby Dick we're talking about. 700+ pages, so something that vastly exceeds the size of the kinds of documents people are likely to attempt with a Notepad class application.
Last not least, this is a thought experiment to demonstrate just how incredibly fast today's machines are, and that if something is slow, it is almost certainly because someone did something stupid, often in the name of "optimization" that turned into pessimization, because doing Doing the Simplest Thing that Could Possible Work™, i.e. brute-forcing would have been not only simpler but significantly faster.
Now the user is either queuing up a bunch of background saves leading to overload or is forced to wait 1s per keystroke.
Well done!
I guess the simple solution then is to tell the user to buy a $3000 laptop just so it's capable of running notepad.