Question about RAM and dual-channel

[John I Tzimisces]

Dear Sirs and Madames,

A while back our PC repairman told me he thought my PC's RAM was improperly installed, and could be running in dual-channel mode.
A few minutes ago, I stopped by his shop and asked again if he could do that this week, how much it would cost for him to do that, etc etc.
The first thing he said was first we'd have to check if my RAM was DDR or DDR2.
How can one check without opening the case, if his or her RAM was DDR or DDR2?

Warning in advance, I have no idea what I'm talking about.

[allthesedamnnamesaretaken]

I'm not an expert, but in order to run in DDR dual-data rate mode, you must install 2 identically sized ram chips into the 2 matching slots on your motherboard if it has 4 slots (not an issue if your mobo only has 2 slots). Ideally, these ram chips should be of nearly identical speed, so you should use the same model from the same manufacturer. They usually sell these in ddr kits with 2 chips from the same manufacturing run.

I'm not quite sure how to check what type of ram you have if you don't want to open your case. It should say on a manufacturer’s sticker on the chips itself whether they are ddr or ddr2. If you know what motherboard you have, you can check its specs online to see if it even supports ddr2. If you have an older pc it may only support ddr.

You might also want to try a program like memtest: http://www.memtest.org/. It’s a program for testing if your memory chips have stability or data corruption issues. You can even test a single chip at a time. The screenshots lead me to believe that it figures out what type of ram you have, amongst other things.

[Ummagumma]

A nice little program called cpu-z (downloadable here) will tell you all you never needed to know about your PC.
The first tab is all kinds of things about your processor, bus speed and related info, but the memory tab will say whether it is running DDR or DDR2, wether it is in single or dual channel mode, and information about the timings (only important if you want to get more of the same memory..) The SPD tab tells you what type of memory is in what slot.
Any questions, just ask...

[Simetrical]

And seriously, don't pay someone to switch your RAM from single-channel to dual-channel mode, if it even is in single-channel mode (and do check that, a lot of these paid tech guys are unscrupulous). Changing from one to the other is something a moderately well-trained monkey could do in two minutes. You can get clear instructions with pictures from anywhere you like and there's essentially no chance of breaking anything or of your computer not working.

[John I Tzimisces]

Alright, thanks for the info guys.
According to CPU-Z, I have two 512 DDR sticks and a third gig stick.

I am supposing this means that my computer is incapable of running in dual-channel mode.

[allthesedamnnamesaretaken]

Take out the 1 gb stick (or put in another 1 gb stick of identical frequency and timing), and it will run in dual channel mode

You will need to make sure both your 512 mb and 1 gb modules are in the correct matching slots on your mobo.

A better way, if you can afford it, is to replace your two 512 mb sticks with a new 1 gb stick. If you are using a 32-bit OS, you can't make use of more than 2 gigs of ram anyways, and it can cause stability issues with programs and games that try to use more than 2 gb of ram.

[John I Tzimisces]

Hrm, isn't there a 64-bit version of XP?
Hrm anywho, I do indeed have the 32-bit version of windows XP.

I suppose theoretically I could sell my old RAM?
*wonders who on earth would buy it*
Seems a terrible waste to just get rid of two perfectly good 512 sticks.
But yes if I do pursue this further I'll be sure to bear in mind buying a gig stick to replace the old ones.

[allthesedamnnamesaretaken]

You can get 64-bit versions of xp and vista, but you aren't going to upgrade for this anyways since you really don't need more than 2gb for any games anyways.

and according to Tom's Hardware (http://www.tomshardware.com/2007/10/...ng/page11.html), the benefits of running in ddr mode is quite minimal. You DON'T get double the speed.

capacity is a bigger factor. running 2 gb in single channel is way better than 1 gb in dual channel

[Doono]

I wouldn't worry about changing your ram to run in duel channel mode, the performance gains are not exactly spectacular and spending money to do it is just pointless.

[spartan_phalanx]

As has been mentioned it isn't worth it to spend money just to get dual channel with what you already have. Save the money and forget about the tech guys as they likely just want to sell you some RAM.

[Simetrical]

Alright, thanks for the info guys.
According to CPU-Z, I have two 512 DDR sticks and a third gig stick.

I am supposing this means that my computer is incapable of running in dual-channel mode.

As far as I'm aware, dual-channel mode operates per unit. I'm fairly sure you can have one pair of memory banks running dual-channel, and another not.

A better way, if you can afford it, is to replace your two 512 mb sticks with a new 1 gb stick. If you are using a 32-bit OS, you can't make use of more than 2 gigs of ram anyways, and it can cause stability issues with programs and games that try to use more than 2 gb of ram.

If you're using 32-bit Windows, you can typically make use of up to 3.something GB of RAM. Possibly somewhat less than 3 GB if you're using a fancy enough video card (or other device mapped to kernel memory), but certainly not as low as 2 GB. By default, applications in user space are limited to 2 GB of addressable virtual memory and therefore no one user-space application can use more than 2 GB of RAM, but

1. You can reconfigure this so that it's 3 GB for user space and 1 GB for the kernel instead of the default 2/2. 32-bit Linux defaults to a 3/1 split. On the other hand, it might not be wise to give user space 3 GB, since apparently video memory gets mapped to the top of kernel memory. If you have 512 MB of video memory you might not leave enough space for kernel data structures in the top 1 GB, and if you have 1 GB of video memory you certainly won't. I think Linux (and possibly other OSes) handle video memory differently, i.e., not memory-mapping it, and so don't have this problem. I'm not certain about any of the foregoing in this point, beyond the first two sentences.
2. More importantly, the remaining gigabyte-plus can be used by other applications, and by the OS's disk cache. It's not remotely wasted.

I suppose theoretically I could sell my old RAM?
*wonders who on earth would buy it*

Nobody.

But yes if I do pursue this further I'll be sure to bear in mind buying a gig stick to replace the old ones.

If you're going to buy a new 1 GB stick, you may as well get the same model as your current one and put it in the free memory bank. That should allow all sticks to run dual-channel.

and according to Tom's Hardware (http://www.tomshardware.com/2007/10/...ng/page11.html), the benefits of running in ddr mode is quite minimal. You DON'T get double the speed.

I did a little digging on that recently, and made a post about it in some other thread. It seems that other reports conflict somewhat with Tom's Hardware on this. In particular, one reported that for copying large files, you do get almost a factor-of-two speed improvement. (Which is interesting. I wonder how many in-memory copies Windows does in a typical file copy. I would imagine zero, but you never know.)

capacity is a bigger factor. running 2 gb in single channel is way better than 1 gb in dual channel

That's almost definitely true, yeah.

[allthesedamnnamesaretaken]

As far as I'm aware, dual-channel mode operates per unit. I'm fairly sure you can have one pair of memory banks running dual-channel, and another not.

I'm fairly certain this isn't possible. To acheive dual data rates, you need both slots of each memory bank to be occupied so that both modules can address the memory controller at the same time. The memory controller wil operate at the speed of the slowest module, which is the single channel 1gb bank.

[Ummagumma]

I'm fairly certain this isn't possible. To acheive dual data rates, you need both slots of each memory bank to be occupied so that both modules can address the memory controller at the same time. The memory controller wil operate at the speed of the slowest module, which is the single channel 1gb bank.

You are right about memory only operating at the speed of the slowest, but dual channel does no make it 'faster'. It makes it a wider connection. 1 800Mhz module and 1 533Mhz module and both will operate at 533.
Dual channel is a bit different, and entirely depends on the memory controller/motherboard. It widens the data stream from 64 to 128 bits (two 'channels'). Some boards/chips will operate with unbalanced memory configurations, most will not though.

[Simetrical]

Hmm, yeah, I think I was wrong. From an Intel white paper:

For the best dual-channel memory performance on motherboards with the Intel dual-channel DDR chipsets, you must use identically paired memory modules in DIMM sockets 0 of channel A and B. Identically paired memory modules must also be used when populating DIMM sockets 1 of channel A and B.

[allthesedamnnamesaretaken]

Actually, I posed this question on driverheaven and apparently there are Intel chipsets that will run in asymmetric dual channel mode: http://www.driverheaven.net/hardware...nnel-mode.html

This whitepaper appears to cover ddr2 chipsets only so it may not apply to John if older ddr chipsets do not have this technology. There appears to be support for dual channel access to memory ranges of the smaller channel capacity, and then single-channel access to higher addresses.

So in John's situation, and if he was using a supported chipset, there would be dual-channel performance up from 0-1gb addresses, and >1gb+ to 2gb addresses will be accessed in single-channel mode.

However, the paper also stated that there are overhead performance issues with operating asymmetrically like this, so it is less efficient than running in full symmetric dual-channel mode.