Moving SSD harddrive to another Mac I currently have my data and apps on a 2009 13" MacBook Pro and want to move to a 2012 13" MacBook Pro.  I want to move my SSD to the new computer as the new one has a standard SATA drive.  I am currently running Yosemite 10.10.5 and the new one is running Mojave.  

Is the new computer going to start up with the change?
I don’t recommend moving drives or even loading a bootable copy. I do recommend a clean OS install and then running migration assistant. That tool has custom code to handle all sorts of useful functions like driver incompatibilities, disabling incompatible software and you just get a fresh clean install with your data and accounts on top. 


https://support.apple.com/en-us/HT204350 (Migration KB)
https://support.apple.com/en-us/HT201462 (Target Disk Mode KB)


Use target disk for the migration Even if you have a solid back up. You could also migrate from your back up.

If you decide to just move the data directly, target mode helps there too.
Place the old Mac into target disk mode and connect with FireWire/Thunderbolt to the new Mac and the new Mac can boot from the old Mac so you can be sure all the drivers and data are good.

note, USB-C target disk is available on very recent machines as well, but FW/TB is more ubiquitous

Always boot and test before you remove any drive and same with moving the SSD. you'll need to get the iFixit or another tear down for the exact models and validate that the form factor and connectors are compatible. Then you will know that physically it should work, data wise it will work so if you put the drive in and it doesn't work, you don't have to guess - you'll know everything was fine except the connections.

Good luck - feel free to ask a follow on question if you can't find the repair manuals for each Mac. There is probably a general question here showing how to take a serial number or the About this Mac to get the exact model number and marketing year.

For me - the colloquially named 2015 MacBook or "MacBook One" is precisely:


MacBook (Retina, 12-inch, Early 2015)
MacBook8,1