Planned obsolescence usually refers to hardware that is designed to become obsolete sooner than necessary in order to enable the vendors to sell more units.
Examples in technology include devices without replaceable batteries, operating systems that grow more compute-hungry faster than necessary, special code to make software run slower on older platforms, etc.
The opposite of planned obsolesence is the long lifetime of Old and Small Technology.
More at https://en.wikipedia.org/wiki/Planned_obsolescence
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Old technology is any tech that’s, well… old.