Hi, Your case is slightly bigger than mine, and I can only get 2 Hard drives in mine. Though, it does look that you can only get 2 H D in. Your specks HERE  says  Up to two of the following 5.25-inch devices: SATA DVD-ROM/CD-RW Combo, DVD +/- RW  Blu-ray™drive, HD/DVD Combo Blu-ray drive

One 3.5-inch USB media card reader
internal 1.44 MB 3.5 inch drive
external USB 3.5 inch drive
internal USB Flash Reader
Up to four 3.5 inch SATA or SAS hard drives (hard drives may be placed in 5.25 inch bays with an optional adapter)

Here is your answer: "Up to four 3.5 inch SATA or SAS hard drives (hard drives may be placed in 5.25 inch bays with an optional adapter", must be talking about that space to the right of your hard drive.

I have the exact same question for a Precision T3500, which appears to have the same case as the T5500.  My T3500 has 2 internal hard drives and 2 internal optical drives.  There are 5 SATA connectors on the motherboard, and the online manual states that a third and fourth hard drive can be installed in the 3.5-inch "flex bay" or the 5.25-inch optical drive bay.  How??  It doesn't say.

You can order these workstations with 2 optical drives and 3 hard drives installed.  I can't find any adapter kit for installing a 3rd hard drive in the flex bay.  I've emailed Dell Tech Support about this, but haven't heard anything back yet.  If I need to buy some kind of adapter, fine.  JUST TELL ME WHAT I NEED ALREADY.

I am tempted to buy a Precision T3500 configured with 3 hard drives and 2 optical drives just so I can see how they do it, and then returning the computer...

I hope these pictures help, I ordered this t3500 with 1 hard drive and 1 dvd drive and a multimedia drive. As you can see I was able to install 3 more hard drives.

Thank you for posting the pictures.  A couple of questions: Where did you get the bracket shown in photo6.JPG (2nd photo) that was used to mount the 3.5-inch HD in the 2nd optical drive bay, as shown in photo1.JPG (last photo)?   In photo2.JPG (next to last photo), there is some kind of plastic doohickey in the bay below your multimedia "drive" and above the USB ports.  In the photo you can see the orange SATA cable behind it.  I'm assuming that you removed this thing (it just slides out, what's it for?) before installing your 4th HD in that bay.  Did you just use screws in the side of the HD to mount the drive in that bay or do you have some other mounting hardware?

Thanks again; you've been extremely helpful.  It's still not clear to me why Dell doesn't make this information readily available.  It is not terribly unusual for people to have more than one optical drive and more than two hard drives in their computers these days.

Oh, my, same question unanswered for me for a Precision T3500.  

Dell's support people have been trying for going on two weeks to find a way to sell me the bracket to mount a 3-1/2" SATA drive in the 5-1/4" optical bay.  They did find a part number but can't find out how to sell me one.

I've found that bracket, or something claimed to be that bracket, searching online in third party ads from places I don't know anything about for anywhere from $40 to $170  -- apparently theyr'e scarce.    That's advertised but not promised available.  

I'm not specifying the number here because I don't know if it's correct.

Dell's support is also currently trying to answer me on how to mount a 3-1/2" SATA  in the 3-1/2" bay (they found contradictory information in their records, one says a mounting bracket is needed there, too, something else says the drive can be mounted without additional hardware.

I haven't pulled the thing all apart but I guess it's time.

I'd just stuff it in there but I'm sure (optimist that I am) that a proper mount would improve the heat dissipation from the drive by carrying some off in metal frame and bringing intake air through the surrounding space.  I hope.

Fantastic.  Thank you Joseflv.  The four screws get screwed into the bare drive, then when the drive is slid into the bay, do the heads slide into a groove "past the tabs" to hold it in place?  I can imagine that's it, I'll get the box open soon and find out.

Hi Joseflv, Thanks so much for the instruction!

I was able to follow until the 6th step, but then I couldn't find one of the SATA cables (the narrower one), but I can find the broader one extended from the CD-ROM. Am I missing something? or do I have to order another cable from Dell?

Thanks!

All of our Dell T3500 systems were ordered with a single hard drive and a single DVDRW drive.  These all shipped with SATA data cables on SATA ports 0 to 2.  SATA-0 and SATA-1 are blue cables that run under the system board and around to where you would mount hard drives #1 and #2.  SATA-2 is an orange cable that runs to the optical drive (CD or DVD).

Unless you ordered a system with additional drives, such as 3 or 4 hard drives or two optical drives, it will not come with SATA data cables for SATA ports 3 and 4.  You can buy a ten-inch SATA II data cable for about $5 online.

The "broader" cable that you are referring to is the SATA power cable.  The one that is attached to the optical drive should have 3 connectors on it.  I attach the last connector on that cable to the third hard drive that I mount in the upper 3.5" drive bay.

To mount a 3.5" drive in the 5.25" optical bay, all you need are a pair of inexpensive brackets like these:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280615685534

The SATA power supply cable for the optical drive will owrk with your hard drive. SATA cables are inexpensive and avaliable at Staples, Office Depot, Best Buy, etc.