Original post by: LikeARabbit ,
iFixit has an excellent hard drive replacement guide for your iMac at - [guide|15796|27" iMac Hard Drive Replacement] Anytime you open your iMac you will need to replace the adhesive foam strips - [product|IF174-005|Adhesive strips] Plastic cards will come in handy. iFixit sells sets of two but old credit or gift cards work fine as well - [product|IF145-101|Plastic cards] The Late 2012 iMacs also require an opening tool to initially cut the adhesive around the display - [product|IF145-219|iMac opening tool] As far as hard drives go you have limited choices in the 3.5" form factor that is native to the iMac. OCZ's Vertex hard drives are available in 3.5" form factor and should work for your application. Alternately you might consider a hybrid drive, one that combines small SSD storage with large traditional platter storage. Seagate's ST2000DX001 is one such model, a 2TB traditional drive with 8GB of embedded solid state storage. Hopefully that helps!