I have 3 SATA HDD and one IDE HDD which I have connected to my desktop. I have data in all of these drives. Is this setup ok I heard the term RAID but not sure if that applies here. Just worried that accessing mutiple HDD will affect the HDD performance in the long run.
Absolutely no issues. The way you've setup is called JBOD.
RAID is to gain certain specific advantages, like reliability, performance or whatever be your need.
And OS accesses only that disk where your target data resides. In fact, life expectancy of a disk should be more in JBOD, just my assumption though.
