The 730x's Quick Reference Guide says it does indeed support 12GB (you can show the link below to the Support if they insist it does not) and it calls for DDR3-1066MHz memory.  While normally you can put faster memory into a system - as long as it is not "too" much faster (usually one or two steps faster is ok), the fact that Crucial.com shows a 12GB (3x4GB) 1600MHz for the 730x leads me to believe that kind of speed increase is acceptable for this system ... although the memory layout of differently-branded DIMM's may affect its compatibility.

One more thing that might indicate the actual root of the problem you are having ... the 730x specifications say that the following DIMM sizes are supported:

DDR3: 1GB, 2GB, 4GB

XMP: 1GB, 2GB

The specs on the memory that you got indicate it includes "XMP memory performance profile".  I will admit to not being familiar enough with XMP to be able to tell you for sure if this is your problem without further study, but I suspect that it is why your memory is not working.

<ADMIN NOTE: Broken link has been removed from this post by Dell>

The technician was going off of the older data in the Manual and internal Training page. This is the part number for the 4GB sticks we used -
N852H 4GB,1066,512X64,8,240,2RX8

I have 3,  4 gig sticks on order from Dell right now. Just waiting on them to fill the order.

Well Dell pushed ot my order again today so I ordered a 12 gig kit from Cruical. 100% guaranteed to be compatable with the XPS730X or they will refund my money.

Well I got my 12 gig kit from Cruical today. Installed the memory and it fired right up .  Part # CT1452847

how would you say the difference is gary? Was there a noticeable performance increase? I thought about looking into those crucial ram or the ballistic ones like you got but not sure if it would be worth it.  I mostly use the computer for gaming.

Performance is radical, it changes everything (in a good way)!

I hesitated a long time because of initial Price, then some people reporting they were having problems upgrading to 12GB (3x4GB).

I just bought last month from Crucial the 12GB kit (4GBx3), Ballistix 240-pin DIMM, DDR3 PC3-12800 memory - Part Number: CT2586855.  (DDR3 PC3-12800 • 8-8-8-24 • Unbuffered • NON-ECC • DDR3-1600 • 1.5V • 512Meg x 64).  Worked like a charm.   I had to choose the 'Alienware Area-51 ALX (3 Memory Slots) ' rig to see it since my 730X H2C model isn't listed.

Don't hesitate one second as prices are actually affordable now, and you get to keep your awesome rig.

I still look at today's i5-i7 & 3D benchmarks and they don't justify replacing my rig just yet.

My rig:

730X with H2C Cooling

Intel Core i7-975 3.33ghz Extreme (@4.16Ghz)

12GB-DDR3 RAM (@1600Mhz) 

Dual nVidia GTX-295 (QUAD-SLI)

Triple 30'' Apple Cinema in Spanned mode

RAID-0 Boot WD-VelociRaptor 300GB (x2) + RAID-0 Data Fujitsu 2TB (x2)

tnx for the that information maybe i will order some soon. I just ordered an ssd for now but I will consider the ram now as well.

So i just received http://www.crucial.com/store/mpartspecs.aspx?mtbpoid=0BCF4D13A5CA7304 and it is running at 1066 not 1600 any idea how to get it to 1600?

Try setting your Memory Ratio (Multiplier)  to 12x from the BIOS. You possibly have it set on 'Auto'.  Else post your config from BIOS and I can recommend tweaks.

By setting memory ratio to 12, are you now running at 1600 ?

As long as XMP is enabled, it will take care of setting all those to the right ones, so you don't need to touch any of them.  The trfc limit is apparently 100 with on the 730x with the last BIOS, but like you, by using the XMP profile it runs higher by itself and seems to work fine.

I presume your CPU BCLK set at  133Mhz, right ?

Here is an extremely useful Intel tool that will give you more precise readings on the speed everything is really going at, live. I've been using the version 2.1:

https://downloadcenter.intel.com/SearchResult.aspx?keyword=%22%22extreme+tuning+utility%22%22

I suggest you check all your BIOS settings and turn all the funky features ON (not off like most people recommend), like SpreadSpectrum, SpeedStep Tech, XD Bit, C-STATE tech.  Your machine will then take proper control and speed up when it need, cool down and be quiet when it can.  It's just my personal experience talking (& I have a lot of it ;-)

Hope it helps, and feel free to ask questions.

P.S.: You already running 12GB now, so even if you don't get it to 1600, you already have 99.5% of the benefit, so cheer up ;) 

Not sure what all I need to change for ram but I just changed the memory ratio to 12. Currently have.

Xmp enabled 

memory ratio 12

qpi is on auto have 4.800gt or 6.400gt as options

then below that i have the things at 

tcl 8

trcd 8

trp 8

tras? 24

trfc 100  (when I got to xmp support information in the bios it lists 128 i think but mine only goes to 100)

twr 12

twtr 6

trrd 5

trtp 6

then 1t or 2t timing currently on 1t

voltage ram at 1.50v

still running at 1066 with those settings.

I followed the recommendation I found on other sites and upgraded my BIOS from v. 1.05 to the hybrid Alienware/Dell a11b BIOS written just for the XPS 730x to take advantage of 12 gb of RAM with advanced timings, but after installing the Crucial upgrade kit, CPU-Z shows these timings:

DRAM 668.2 MHz

FSB:dram 2:10

CL 9

tRCD 9

tRP 9

tRAS 23 clocks

tRFC 107 clocks

CR 1T

That doesn't seem right, and is much slower than the JEDEC #5 and #6 settings reported for this RAM in CPU-Z.

My first thought was to go into the BIOS and ensure XMP was enabled so the JEDEC settings of the RAM are being read, but under Frequency and Voltage I don't see any XMP settings.  Is this something unique to the a11b BIOS I flashed?  If so, I'll set the timings manually if anyone can tell me what they should be

where did you find the a11b bios and is it safe? how to install?