Studio XPS 9100, reads only 1/3 of installed memory

Since I know someone will ask..

I'm running BIOS version A04.

Windows 7 Home (SP1) reports 4GB as well. I don't have my bootable Linux on me or I'd use that to confirm.

Worth noting: All parts besides RAM are stock, except for an added (replacement) network interface card.

Yes, looks like it's tri-channel memory.

https://www.dell.com/support/home/us/en/19/product-support/product/studio-xps-9100/manuals

Notice which set of 3 DIMM slots comprise the Primary Memory Bank. Machine should run with only those 3 DIMMs installed.

Install original memory and make sure you did not damage your motherboard. Once it POSTs and boots, an ePSA test or memtest86.com should confirm that.

I confirmed that something is wrong with the slot before my OP by interchanging the DIMMs 

Just the same, I ran memtest. But now it gets weirder: No errors found! 

Any clues about how my 3x4gb install can pass memtest, yet  show only 4gb, not 12gb (expected)? System is 64 bit Win 7 Home which I know 32 bit is limited to 4 gig - but I'm checking in CMOS anyway. I ask because while i guess I'm returning the ram (since I need a mobo), I'm not reporting it defective either I suppose, since the chips all seem to work.. but just wut exactly is going on here, ya know?

You chose HIGH Density cheap ram and its not ever going to work.

Must be LOW Density and Dual or Single rank.

Must NOT BE ECC or Registered or buffered or Quad rank .

http://www.crucial.com/usa/en/compatible-upgrade-for/Dell/studio-xps-9100

CT2793211

• DDR3 PC3-12800 • 8-8-8-24 • Unbuffered • NON-ECC • DDR3-1600 • 1.5V • 512Meg x 64 •

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@Savemejebu5 wrote:

1. I confirmed that something is wrong with the slot before my OP by interchanging the DIMMs 

2. Just the same, I ran memtest. But now it gets weirder: No errors found! 

3. Any clues about how my 3x4gb install can pass memtest, yet  show only 4gb, not 12gb (expected)?

4. System is 64 bit Win 7 Home which I know is limited to 4 gig - but in CMOS too?

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1 & 2. I've never seen a bad MB/slot/DIMM/etc. pass MemTest86.com . Are you sure you are reading it right?

3. No. But what you should be trying is 1gb-x3 or 2gb-x3 (your old DIMMs).

4. No, there is no such limit.

@speedstep : I verified this Ram would work through the manufacturer of my computer, anecdotal evidence, and the manufacturer of the ram. It is compatible by all accounts except your own. But okay, this problem seems to go elsewhere anyway..

PS thanks for posting the limits. I was trying to communicate that i should not be limited to just 4gb

@Tesla1856 : tried the computer with many RAM configurations. Replaced the CMOS battery to be safe.

Configs that fail to post: aftermarket 24gb (obv). original 9gb (hm!). Any single or dual Channel configuration (I think this is as designed). So.. Any configuration involving all 6 slots fails now. Bad slot I think.

Configs that Do post: original 6gb (3x2gb in slots 1/2/3), original 3 gb (3x1gb in slots 1/2/3), new 12gb (3x4gb in slots 1/2/3). 

Based on this I've figured one of the slots (4/5/6) is bad.

What's strange about the configs that Do post is that BIOS always shows just one-third of the memory (2gb when there are 6gb installed, 4gb when there are 12 gb) and it passes memtest86 which also shows that same amount, so it's obviously not testing the other two thirds. Based on that I would say I have bad slots in 1/2/3 as well.

Maybe I missed something though.. 

High density ram will show less than the amount installed.

That ram is not compatible.

Tri channel compatible ram works fine in all 6 slots when its the correct ram.

The linked model from crucial works fine in the XPS 9100 as well as the precision T3500 etc.

DDR3 PC3-12800 • CL=11 • Unbuffered • NON-ECC • DDR3-1600 • 1.35V • 512Meg x 64

@speedstep

Yes. However, since the computer is showing less than the installed RAM - even with the the original sticks- EDIT: and it will not post it in single Channel mode regardless of RAM, I can only conclude the issue lies elsewhere. 

EDIT: See reply to other user above

Also see first post and amended thread title which reflects the issue I now find needs diagnosing. 

These issues occur with new memory as well as original memory. I am unable to test any one RAM stick in this system, as the system fails to post and throws the "no memory detected" error (two beeps) when in any single channel RAM configuration. Nonetheless, I am returning the g.Skill RAM package (can't use them anyways, and apparently I need something else anyways, according to user speedstep).

Because of that, I am giving up hope for actually determining which slot or stick is bad until I get more advice. At this point, I am looking for any additional thoughts about that before I order any more parts (just paid a $25 restock fee for this RAM I am returning)

Yea @Tesla1856 I am just unconvinced the issue is only that, since I can't get the 6gb I install to even be recognized (again, it posts and recognizes one third, so that means I can only get 2gb of it to work, and must keep all the chips in or I face a memory error)

..and installing six chips causes the memory error code too (I guess it's truly on its last legs).

Savemejebu5,

I own the Studio XPS 9100's predecessor, the Studio XPS 9000 [aka 435T] which uses the same LGA 1366 CPU socket and X58 chipset.

If I recall correctly, I too ordered G.Skill RAM to upgrade the memory and had to return them since my machine wouldn't post with them.  This prompted much research to understand why as I wanted assurance new DIMMs would work.  Also, I was trying to push the limits on fastest and maximum capacity RAM and there wasn't a whole lot of info out there for my 9000.

Here's a post of a similar 9000 owner failing to get G.Skill's to work.  He opted for Crucial Ballistic Sport, which I also have (6x8GB, 48GB total) after upgrading from Kingston HyperX (6x4GB, 24 GB total).

As to why I summarize here.  The 9000 (and likely 9100) ignores XMP memory entries in the DIMM's SPD, using only the JEDEC entries.  The Ripjaws are targeted at motherboards with ability to use the XMP entries for overclocking the memory.  The Ripjaws JEDEC entries don't seem to match up to standard memory speeds.  So, the Dell Studio XPS machines can't find a matching 1066 or 1333 entry in the JEDEC and don't post.

The Crucial Ballistic Sport and Kingston HyperX have more or less standard JEDEC entries, which is why they work.  This can be shown with CPU-Z, SPD tab.  You want memory that has a 666 MHz (corresponds to 1333 memory) Timings Table JEDEC entry.  Memory without a 666 entry but with a 533 MHz (corresponds to 1066 memory) would also work, but be slower.  Note purchasing single, double or triple DIMMs all work together provided they're the same.  For example, I purchased 3 kits of 2x8GB because it was less expensive than singles or 3x8GB kits.

I would buy 1333 or 1600 Sport or HyperX - but you may have to buy in singles (expensive) or doubles.  Alternately memory from likes of Kingston, Crucial, or search online for the CPU-Z SPD entries of the memory I was considering to make sure it has the JEDEC entries you need.  If I recall correctly, finding memory with 666 JEDEC entries wasn't easy or possible or didn't work in the XPS 9000 - 533 was available and did work, though.

A Dell forum thread with at least 2 different brands of working 4GB DIMMs in the 9100 here.

@Tesla1856 - yes that's why I mentioned my training and experience, to indicate that I'd be surprised if my own hands caused this issue.

However it seems this was two issues: the hardware failure, anda that the compatibily research goes a little deeper to reveal both the manufacturers were wrong about this (Dell and g.Skill lol) as well other board users (in another thread, users were reporting this specific RAM to work in the 9100)

@Techgee that's useful. im not doing a RAM upgrade to this mother board now -since the dual and or triple channel circuitry seems to be in state of failureI- but someone will be glad for the clarification. Going to recommend motherboard fix, or replacement with new one capable of DDR4