Instruction: Generate an answer to the question by utilizing the information contained in the document.

Input:
Question: Does this dock see 1 big drive with 2 hard drives plugged in or is it two separate drives?
Document: If your host is not port multiplier capable, the Thermaltake dock will only handle one drive at a time. I have a StarTech dual-drive dock that has two separate eSATA ports which requires two eSATA cables and 2 eSATA ports on the host computer.USB hard drive connection is a bad joke, as it is extremely slow. eSATA is pretty much as fast as the drive itself.
If you're going to go with a drive bay, BlacX is the way to go BUT STAY AWAY FROM THE DUETS. I've had two of these things fail on me. They worked fine for a few months but after a while they completely malfunctioned and corrupted my data when I plugged two drives in. After a while after that they wont even work reliably for using a single dock. I've been using the same Single Bay BlacX for at least 2 years now, just buy two of those if you want reliable performance.
Thermaltake fails to inform buyer on packaging of need for port multiplier for eSata dual drive compatibility. The box states: "Read & Write 2 Hard Drives simultaneously." It also states: "Rapid Data Access & Exchange w Single eSATA or USB Cable Connection." NOWHERE does it even mention that you should check to see if you have port multiplier capability (which is absolutely necessary to run two drives over one eSATA cable).At this point most systems DON'T have port multipliers.
This product works perfectly with 1 or 2 sata. I've tested it in raid 0, raid 1, and jbod. All work. You can see my fan mod in the pics. It took me about 2 minutes to find a solution to the heat problem. The deal is any hard drive that doesn't have a fan blowing on it isn't going to be happy. I've been a system administrator for a data center for 15 years. If a hard drive has a fan blowing on it, it doesn't fail.
I have had this for 1 month. I find it very useful. Works like a charm with my Win 7 pro 64 bit OS PC. I have tried it with USB and E sata connections. The e sata is fast. It recognizes 2 drives in the dock easily and transfers between the two drives is very fast.HDDs get quite warm. The con is that the on/off button lights up both the LED lights whether one or two drives sit in the dock. Good value for the $.
Things it did: The dock work as advertise, when I put in my HDD, computer could see them, and I could write/read off them. Overall it was a good product, held the HDD tightly in place.Cons: Only one power button for 2 hard drives.
I bought this one instead of having 2 single bay dock and inserted my 2 X 1 TB hard drives.The problem is, The Hard Drives ejects automatically. I have to press the Blacx power button very often. Because of this issue, I miss the schedule backup (Time Machine and CCC). This (Duet) is very good concept. But, It is not working for Mac environment (Unfortunately!!!!!! ).
But I sprung for it anyway. It arrived; I popped in the two 1 Tb drives; plugged in the power; plugged in the USB cable to a Mac Mini (running Snow Leopard); voila !! The Mac asked me if I'd like to initialize the drives -- which I did.From that point on they have functioned perfectly. I've backed up over 200 Gb to each of them without a hitch. Heat? What heat?
XP requires you open up the device manager and "scan for hardware changes" to get it to "see" the drive.What this unit could do better:1) Be priced reasonably (~$20)2) Have the drives go to sleep when the attached computer goes to sleep.3) Include USB 3.0 connectivity4) Include an extra eSATA port for connection to host that are not port multiplier capable
Details specific to Dell Studio XPS 16 laptop:I tried to use 2 drives via eSATA on my Dell Studio XPS 16 laptop. The laptop could see only drive 1. The message says "A storage device was connected. If this device is a port multiplier, only port 0 of the port multiplier will be active. "After much effort, I found a document from Intel saying that the PM45 express chipset, which the XPS 1640 uses, does not support port multiplier.
Answer: it will show both drives love mine have used it for years they are a good product.