How many software updates does an apple device go through?

Apple usually does not give ios updated to older devices such as ipad 1, iphone 3gs, ipod touch 4g and older so i want to know that how many updates does a device go through like the ipad experienced ios 3, 4 and 5 if i'm not wrong. So is it true all the devices only go through 3 updates?

I think I only ever updated my last iphone once. Older hardware like 3, 3GS doesn't have the horsepower to support the new OS so usually only the last several versions are supported on new OS's

Normally when you buy the newest device from apple (like the iphone 5s in this example) it will run for like 3/4 updates. That means that the iphone 5s latest update will be ios 10 (ios 7, 8, 9, 10).

This isn't always the case because ipad1 only had 2 ios versions. Ios 4 and ios 5. But i think 4 updates would be a good gamble.