Trying to understand RAM

[truenorth]

On a Dell XPS desktop running xp pro sp3 i have 4 available RAM slots. According to a Crucial scan i can have up to 1 gb of RAM per slot. I won't go into the type of RAM as i don't think it is relevant to my question. It also stated that if i am running a windows 32 bit system (which i am) it may only recognize 3-3.5 gb of the total of 4 gb if it were installed and if i wanted to be able to access all of it i would need to upgrade to a 64 bit system.
  Now here comes the part i want to understand. I currently have 2x256  MB in slots 1 and 2 and 1x512 in slot 3 and slot 4 is empty. It states that RAM modules MUST be installed in pairs. So if that is so and i only have 1 512 why is my "system" showing i have 1 gb of RAM installed (which of course i do). If they must be installed in pairs why is it not showing 512 mb of RAM? truenorth

[BC_Programmer]

because crucial is probably wrong.

[jason2074]

You meant a separate reading for the 512 RAM module inserted on slot 3? Aside from the pair of 2x256 module for slots 1 and 2.

[Broni]

We're talking here about dual channel RAM, which is RECOMMENDED to be installed in pairs.
It doesn't mean, your computer will not read, or use all RAM.
Your RAM will be just slightly slower.
Actually, from what I read, in reality, you won't notice any difference ( to the naked eye).

[Broni]

http://en.wikipedia.org/wiki/Dual-channel_architecture

There have been varying reports as to the performance increase of dual-channel configurations, with some tests citing significant performance gains while others suggest almost no gain.

Tom's Hardware found little significant difference between single-channel and dual-channel configurations in synthetic and gaming benchmarks (using a "modern" system setup). In its tests, dual channel gave at best a 5% speed increase in memory-intensive tasks.[3] An older comparison by laptoplogic.com found a speed advantage of up to 15.3% for the integrated intel GMA900 graphics when utilizing dual channel memory.[4] The test results published by Tom's Hardware had a discrete graphics comparison.

The difference can be far more significant in applications that manipulate large amounts of data in memory. A comparison by TechConnect Magazine demonstrated considerable gains for dual-channel in tasks using block sizes greater than 4 MB, and during stream processing by the CPU

[truenorth]

Thank you all ( particularly Broni for the extensive explanation). I tend toward being a literal person that believes words have meaning and when i see "must" to me that does not imply choice. truenorth

[Broni]

You're very welcome

[Hearts on Fire]

Hm, that article (http://www.tomshardware.com/reviews/PARALLEL-PROCESSING,1705-15.html) is from 2007, too. I was going to say maybe it's old and was using hardware that didn't need the extra bandwidth… isn't dual channel supposed to effectively double the amount of bandwidth your system has? I guess it's just not a bottleneck and the memory controller for the FSB/hypertransport just is too slow to benefit? I'm actually really curious about this now.

[Computer_Commando]

On a Dell XPS desktop running xp pro sp3 i have 4 available RAM slots. According to a Crucial scan i can have up to 1 gb of RAM per slot....

Don't be so sure of that, either.  I have a computer where the documentation and manufacturer and Crucial specify 1GB in each of 2-pair, dual channel slots, for a total of 4GB.  The maximum it will recognize in the BIOS is 2.7GB, with 2-1GB pairs (4GB).  When booted to WinXP (32bit), CPU-Z reports 4GB, Windows reports 2.7GB.  BTW, I suspect your Dell is DDR, as is the one I am referring to.

[truenorth]

C-C , This is what i have re RAM,truenorth

[recovering disk space - old attachment deleted by admin]

[Computer_Commando]

As I suspected, it's DDR.  Dual-channel was a feature of PC3200/DDR400; if it increases speed at all, it's not noticeable.  DDR wasn't around very long before DDR2 came along.  DDR is 2-3 times the cost of DDR2.  If your plan is to increase the RAM, get rid of the 1-512MB, get 2-1GB, keep the 2-256MB.  2.5GB will be plenty.  This is the RAM configuration I have on mine.  You will then be running in dual-channel mode.

According to my manual, RAM configuration allows all dual-channel or no dual-channel, i.e. you can't have 1-bank at dual and the other not.

http://en.wikipedia.org/wiki/DDR_SDRAM

[truenorth]

C-C,Thank you for your suggestion. I already have the Crucial part I.D. (for comparison with other brands that may be less expensive) and intend to look for some additional when i make my fall trek to my favorite tech store in Atlanta. I will take your advice re the purchase and placement of the RAM. truenorth

[Computer_Commando]

More often than not, the DDR comes in matched pairs, 2-1GB in one package.  They usually will be sold as a "Dual-Channel Kit", like this:  http://www.newegg.com/Product/Product.aspx?Item=N82E16820178101

[truenorth]

C=C ,Surprising new developement. I ran a Crucial scan after my last post on my wife's Cisnet CA-8003B and lo and behold it uses the same RAM. Hers only has one 512mb in one of 4 slots. Hers is claimed to be only able to utilize 2 gb total. So it looks like my soon to be removed 512 along with 2 more 512's to be purchased may have a new home. Yes i am aware that probably they won't be the same mfg. so therefore may not work. But I'll cross that bridge when i come to it. I was granted a very rare privileged to even be allowed near her computer (no idea why  ) truenorth

[truenorth]

Just a little footnote and elaboration re my last post as i think it may be worth knowing by those that might take as gospel whatever the Crucial scan says. When doing the scan on my wife's Cisnet it actually was only able to identify the value of the RAM (512mb) nothing else other than what slot it was in and that the other 3 were empty. If that occurs Crucial offers that you contact them (as part of the scan process) via message. They ask a couple of questions but a unique code is applied to the scan so they obviously can correlate . Now doing an independent search on the computer i found numerous references to  all the aspects of the RAM for that precise computer. It clearly stated in all cases that the maximum amount of RAM that can be used is 2 GB.Crucial sent me an e-mail after their analysis to complete the data information of the earlier scan. They stated that it could use  up to 1 gb of RAM per slot for a total of 4 GB. I have re contacted them to point out their error. But as BC_ P said in his post #2 "because crucial is probably wrong." is possible to be correct. So one has to take Crucial's results with a grain of salt it seems. truenorth