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Old 15. Mar 2016, 03:27 AM   #1 (permalink)
Join Date: Jan 2009
Location: SE Wisconsin, USA
Posts: 14
Question Memory upgrade - but how?

Forgive me for asking this simple question but I am a software guy... I have this hand-me-down desktop system, no docu:
Dell Studio XPS 435 MT (ca. 2008-2009)
Service Tag: 1KLCMJ1
Memory: PC3-8500F, currently installed 4 x 1GB
Max memory capacity 12GB (according to SIW).

About all this the Dell web site naturally(?) is quiet like the Northwoods in fresh, deep snow; so here goes.

I believe to have read that DDR2 memory needs to be paired (size & speed) or you loose speed. Is that true for PC3 (= DDR3) as well?

Or could I just put 3 x 4GB in the mobo for full capacity without losing speed?

And last (but by no means least): I don't find anywhere PC3-8500F denoted memories, only PC3-8500. Is this difference relevant?

BTW: The mechanics of installing memory chips are trivial and NOT in question.

Any enlightening pointers are appreciated; TIA.

Last edited by eikelein; 15. Mar 2016 at 03:36 AM.
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Old 15. Mar 2016, 11:55 AM   #2 (permalink)
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Join Date: Jul 2010
Location: New Zealand
Posts: 1,741

Memory upgrade
I would go to a few third-party memory sites to see what memory is required and what the maximum capacity is. It takes a bit longer to find it at Dell because Dell may no longer sell memory for your system. As it turns out I couldn't find it for sale at Dell.
Capacity is 24GB in six slots. Two banks each with three matched modules (see Service Manual):
e.g. DDR3 PC3-12800 8-8-8-24 Unbuffered NON-ECC DDR3-1600 1.35V 512Meg x 64
Type: DDR3
Size: 4GB
Pin Count: 240
Speed: PC-10600 1333Mhz
ECC: None
Registered: No
Voltage: 1.5V
CAS Latency: 9
Configuration: 512Meg x 64

I looked at your configuration and can't figure out where you got the description "PC3-8500F" The suffix F usually denotes fully buffered memory which would be expected to have a different connector so it is not interchangeable with unbuffered memory. The issue is that AFAIK there is no DDR3 fully-buffered memory and I couldn't find that requirement at Dell or the memory sites.

Matched memory is required on your system
Dell recommends matched memory for your system so that is the safest way to go. Up to two sets of matched memory with two to three matching modules in each set.
This doesn't mean that other configurations won't work but it is at your own risk.

Matched memory is not required on all systems
In general, DDR2 and, likewise, DDR3 memory does not always have to be matched and many motherboards allow unmatched.

There are two ways they are commonly matched but note that sometimes, for some strange reason, matched memory just don't work and acts like unmatched.
  • matched product i.e. same brand, same model. This has the best chance of performing exactly the same so if it just says matched this is usually what they mean.
  • matched specs i.e. can be different brand or different model but should perform the same.

Any other combination is definitely unmatched and the performance is set to the capabilities of the slowest module.

Matching becomes more important if you want dual-channel operation. This is where the two modules can be accessed at the same time and the two single channels are combined as one dual channel to the memory controller. That means you can get twice as much data in one memory read operation. The modules need to be matched to ensure that they both perform the same otherwise the data won't be available from both channels at the same time.

Dual channels is a form of parallelism where the benefits depend upon the purpose it is being used for. So it is no use getting two channels of data if the first channel provided what you needed and the data on the second channel is superfluous. Testing with benchmarks and real world applications show that most people get little benefit, maybe an average 5-10% improvement in memory performance, from dual channel.

Personally, I try to match modules for reliability more than performance. One reason is that a motherboard can run a module above its spec because it tested OK but the memory later fails to perform. Because memory problems can be hard to diagnose I try to avoid them so I prefer reliable brands I know rather than any cheap brand I don't know. All memory has the spec as a threshold so some exceeds it consistently and other only just makes the cut. Those that are close to the cut are more likely to fail. Whereas some of those reliable brands have memory that is so good that it is effectively good enough to be higher rated.

I don't care about dual channel because I find that system performance is hardly ever a problem - I don't play high-end games - compared to more than 10 years ago when basic tasks like compiling programs, watching videos, and even calculating spreadsheets constantly hit the limits of my computer systems. Back then testing DDR2 I could get an average 4-8% real-world improvement in memory performance on my systems.

One last thought; if it is a choice between 8GB of matched memory and 16GB of unmatched memory, I would generally go for double the memory because memory is faster than disk.
Better to light a candle ... than to curse the darkness.
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