Adding old laptop HDD to new build, possible?

and any other drive you connect to your motherboard will be a SLAVE drive.

strollin beat me to it but I thought it important to reiterate as proper (or current, in this case) terminology is, IMO, important to avoid confusion.

Because the SATA interface supports only one SATA drive per cable, there is no Master or Slave. Only primary (or boot), secondary, tertiary, etc.

Otherwise, I agree with TechnoMage2016 and for a temporary task, you can just connect it as a secondary drive, as I indicated above. If your cables are long enough, you can have your drives sitting on the desktop, or just let them hang as long as the drive, and especially the drive's exposed controller board does not contact anything else. Or you can mount this drive into a spare drive bay and make it a permanent secondary drive for extra storage.

Id rather not let my case be open with it hanging there, especially since my room is carpeted and I have animals as well. I dont have a problem mounting it since Ill just format it and use it as some extra space anyhow.

Ill get to the task this week but thanks for the suggestions, glad to know it should work fine!

Id rather not let my case be open with it hanging there, especially since my room is carpeted and I have animals as well.

"Hanging" the drive in that way should only be done if you plan to hang it, immediately copy off the files (or wipe the drive), then disconnect when finished. It is strictly a quick, temporary option - not a setup to be left (especially unattended) for any length of time.

My bad. I suppose I meant I dont have a problem mounting it and leaving it in there since Im gonna format it for extra space regardless. It'll only take a couple minutes to screw and plug in anyways so I dont mind.

Everything was working as intended today when I plugged in the hard drive and moved everything over. Thanks for the help everyone!