Speaking of yesterday's dysfunctional keyboard, I usually keep a supply of spare parts on hand. For example, somewhere here I have a spare mouse, a few floppy drives, and a power supply or two. I usually have a spare keyboard, too, but I keep spilling things of them.
All these components are fairly inexpensive, and don't change very much over time, unlike CPUs and hard drives, which continually get bigger & faster & cheaper. I've never had to replace a dead CPU (knocks on wood), but just about everything else has needed replacing at one time or another. Sometimes you don't have time to run down to the local CompUSA for some small part.
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I also noticed that I don't like USB keyboards & mice (actually, I prefer *trackballs*, which are easier on my tendons), and I don't like wireless input devices, as they seem slow (laggy) ,, even tho most of the KBs & mice on the shelves at CompUSA last night were USB/wireless.
I used to have even more spare parts on hand, but friends sometimes call at odd hours of the night, saying things like, "Dude, my mouse just died. I am so screwed. Do you have an extra I can borrow?" They promise to replace them, but always seem to forget. [You know who you are.]