SSD upgrade to iMac 2010

woody and sam are spot on.

woodmeister is correct, not all SATA III 6G SSDs are backwards compatible to SATA II 3G.

(you need to make sure, that SSD is backwards compatible)

samtenor is also correct, you need the in-line sensor cable to properly complete that task.

(otherwise you will have nothing but fan and SMC problems)

You must first install Snow Leopard from the software restore disks that came with your computer when it was new.

Snow Leopard Erase and Install

If possible be sure to back up your files.

1. Insert Snow Leopard DVD into the optical drive and restart the computer.
2. Immediately upon hearing the chime hold down the C key.
3. Release the key when the Apple logo appears and wait for the loading to finish.
4. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Utilities' menu. After Disk Utility loads select the out-dented disk entry from the side list (mfgr.'s ID and drive size.) Click on the Partition tab in the Disk Utility’s right window. Set the number of partitions to one (1) from the drop down menu. Click on the Options button and select GUID, click OK button, set the format type to MacOS Extended, Journaled. Finally, click on the Apply button.
5. After formatting has finished quit Disk Utility. Continue with the OS X installation and follow the directions.
6. When the installation has finished the computer will restart into the Setup Assistant. After you complete the Setup Assistant you will be running a fresh installation of Snow Leopard. Open Software Update and install the recommended updates.
7. If you are planning to sell or give your computer away, then do the following: After you reformat your hard drive and reinstall Snow Leopard, the computer restarts to a Welcome screen. To leave the Mac in an OOTB (Out Of The Box) state, don't continue with the setup. Instead, press Command and Q keys to shut down the computer. The Setup Assistant will guide the new owner through the setup process after he/she turns on the computer.
8. Download and install Mac OS X 10.6.8 Update Combo v1.1. if needed. It is not needed if you are selling or giving away the computer.

If you still have the High Sierra installer available then you can try installing High Sierra again. Otherwise, you will need to re-download it on the Purchases page in App Store.

Hi:

I usually downloaded the OS and made USB boot drive to save some time, since I have few Macs in the house.

However, you already have another MacBook Pro -- and you are replacing iMac with SSD. This might save you some time for "rebuild" etc.

https://www.macworld.com/article/3204672/macs/how-to-create-a-bootable-macos-hig h-sierra-installer-drive.html

One more note: Because it is 2010 iMac, be aware of the "fan" might go "full blast" without any modification.

Personally, I chose in-line thermal sensor ( OWC Digital Thermal Sensor for 2009-2010 iMac HD Upgrade ).

There are other few softwares hack to control the fan issues from the web, you can Google for them

Good Luck

Sam

The 2010 iMac has a SATA 2 controller and the Samsung you bought

is SATA 3. In theory the SATA 3 should be backward compatible. However,

in practice many SATA3 drives don't work well on Mac SATA2. Also,

Samsung SSDs seem to randomly have issues working with Macs.

The only thing I would suggest is to try a PRAM reset which reloads

your hardware configuration (macOS Sierra: Reset your computer’s NVRAM or PRAM).

Otherwise, I suggest getting another SSD. OWC

Apple Mac Upgrades - RAM, SSD Flash, External Drives and More

has SSDs that have been rigorously tested for Mac compatibility.

One other item of note, getting a super fast SATA3 SSD won't

reach that level of performance since, if it's compatible, will only

transfer data at SATA2 speeds.