Why does a GCU have an integer counter, does it need to count something to measure time or cycles of something?
That's a question for the hardware guys.
If all modern computers are coded in 64 bit sizes, why did Boeing stick with 32 bit.
A "counter" is basically a unit of data storage in memory and the associated software that manipulates the value being stored, e.g. increments the value and tests it against limit(s). Computers typically have instructions that let them access memory in chunks smaller than the default size, and to not waste memory (which for critical real-time devices can be expensive) the programmer selects a size appropriate to the need.
I gather, from googling it (nothing of which I understood anyway), integer counters are fairly common in computing software, so how do banks not have this problem as their computer hardware boxes have times between power downs measured in years.
This 787 counter counted units of time, so it was a timer. You'd have to know what it was for and why it was designed to force the hardware it controlled into some inoperational mode when the value became zero. It could have been a valid reason e.g. the device had reached a critical time limit where it had to be shut down and lubricated and the problem the program designer didn't allow for was that that service could have taken place without powering off the device and resetting the timer/counter.
If software is not hand coded, ie someone pounding away on a keyboard writing lines of code, how is it written if it's not hand coded.
Programmers may insert into their own program software modules written by other programmers. Hand-coded, but by others' hands.
(The design fault here is that the software does not count characters I've typed within a quote, so I have to say something I didn't need to say outside the quote or it will flog me because my message was "too short".)