Apple just gave a big sign that it has changed its approach to desktop computers after it was forced to make an apology of sorts to pro Mac users a few months ago. One of the new iMac computers it launched earlier this week has replaceable RAM and an upgradeable CPU, iFixit discovered on Wednesday. This means that people who buy Apple's latest iMac with 21.5" Retina Display, which costs $1299, will be able to swap in newer versions of key components to help their computer last longer. "A tinker-happy user (armed with the right tools and guide) could at least double the base 8 GB of memory, turning their new iMac with Retina Display into an iMac Semi-Pro," iFixit's Julia Bluff wrote.