Recently someone brought me a non-functional laptop computer. The problem turned out to be a dead hard disk. As far as I could tell, the platters inside weren't even spinning.
The laptop owner needed the machine fixed as soon as possible, so he went to the local Best Buy with a printout I gave him from the Best Buy web site for a particular hard disk model. I had reviewed all the laptop hard drives in stock in that particular store and chose one with a low capacity, as his needs were modest, and a long warranty.
Despite the claims of the web site, Best Buy did not have that particular hard drive in stock.
The salesperson suggested another hard drive, priced a couple dollars above the original one. Can you guess where this story is going? Hint: the computer in question was about four years old.
Best Buy sold him a SATA hard drive.
Until recently all hard drives in personal computers used an IDE (also known as ATA) connection to the motherboard. Servers often used a SCSI connection, but IDE was the standard for personal computers. In the last year or two, the new SATA connection standard has become very popular.
The Best Buy salesperson didn't bother looking at the hard drive I suggested to see if it was IDE or SATA. They didn't bother asking how old the laptop computer was. Anyone selling hard drives for computers should know to ask if the computer accepts IDE or SATA. And any four year old laptop is using IDE.