Procedure how to replace SSD drive in a 2010 27" iMac

There are two directions possible here. The first is to replace your current 3.5” HDD with a 2.5” SSD. If the drive has failed that is what I would do following this guide Installazione dell'SSD nell'iMac Intel EMC 2390 da 27"

If on the other hand you are trying to improve you’re systems performance then adding the SSD would be a smarter direction! Following this guide Installazione del Kit Doppio Disco Rigido nell'iMac Intel EMC 2390 da 27"

In either case you will need to make sure you get the correct SSD for your system. Most drives today are fixed speed SATA III (6.0 Gb/s) whereas your systems SATA port requires a SATA II (3.0 Gb/s) drive as its I/O is not able to handle the higher data rate of the faster drive. As it turnout there are a few auto sense drives which can match the systems I/O needs as an example a Samsung 870 EVO SSD Note the Interface line clearly states it supports the older SATA speeds: SATA 6 Gb/s Interface, compatible with SATA 3 Gb/s & 1.5 interfaces. Make sure which ever drive you go with clearly states support for the slower SATA II (3.0 Gb/s) data rate.