Answers...

to commonly asked questions.

Do updates slow my computer down?

Is slow performance related to the need to upgrade and, if so, why.??  
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It is true that every time we update our computers or iOS devices, each update asks the processor to do just a little more. Be it graphically or within calculations. However, there are rare cases where updating the software will solve slowness issues which may be caused by the current operating system’s own problems.

Generally you can regard each computer or iOS device as having a limited number of upgrades within its life before its usefulness expires. I would say that number is around 4 major upgrades. In other words, if you buy a computer with 10.5 installed, I would expect it to run up to 10.9 with each upgrade making the computer a little slower than the one before but eventually being unable to update to 10.10. In terms of iOS, the same is true. Buy a new phone running iOS 8 and expect it to be ready for replacement by around iOS 11.

These are just estimated lengths of time of course. Apple eventually cuts off older devices by no longer supporting that particular device’s older processor in future updates.
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