does memory need to be symmetrical?

i have 2 1gb sticks right now and im looking to replace one of those with a 2gb, for 3gb total. in the back of my head i keep telling myself that the slots need to be equal, 1 and 1 or 2 and 2. but that doesn't seem right.
does anyone know whether or not i can put a 2gb and 1gb?

thanks

 

I think they have to match for dual-channel to work. Unmatched pairs will operate fine, though.

 

thanks capntang. im not sure i understand what you mean by dual channel?

 

Dual channel gives your laptop an extra boost in performance. However, having more memory will yield more performance than dual channel. In your case, having 3GB will be better than 2GB, even though 2GB gives you dual channel.

 

ahhh, thanks so much guys. appreciate it.

 

i have 3 gb..right now and it seems to be quick...not sure how fast dual channel would be...can anyone say? thanks

the thing is 32bit vista can only handle 3gb..so it gets kind of shady here

 

In theory, dual channel would make memory transfers (not to be confused with general operations) twice as fast. With DDR2 memory is interleaved so that locations in physical memory are alternated, minimizing dependencies on settling times of a single DIMM

 

perfect...thanks for your input renee

 

dual channel will still work with 1GB + 2GB config. I have it on mine and its still dual channel. It may personally feel better when its symmetrical, but it doesn't have to be.

 

how do you check if you are running dual channel on your pc? Thanks

 

Assuming you are talking about mainstream 200-pin SO DIMM DDR2 RAM, then yes you can indeed.

On a side note, just remember that in case the two sticks are of different speed, i.e. 3GB RAM (2GB 667MHz + 1GB 533MHz) will only run at the lowest speed of the 2 sticks, i.e. 533MHz. But I assume they are both 667MHz (PC5300) modules?

Not quite correct guys. But you are right about them running fine. 2GB + 1GB will also be running in Dual Channel mode, but in "Asymmetric array mode" rather than "Symmetric array mode" that you get when having 2 identical sized modules (i.e. 1GB + 1 GB). The speed difference is in my experience very negligable and is only noticable when running certain benchmark applications. Bottomline, assymetrical dual channel compared to symmetrical will maybe be 5% slower in some synthetic benchmarks. Real life performance however = no difference. This is my experience.


Also note that 3GB in general will be better than 2GB as Sp00n said, but this is only if you are able to utilize that extra RAM. Most people will not noticably benefit from the extra 1GB RAM, as they never make optimal use of 2GB in the first place, as most users are not power-users. 3GB can actually make your PC seem a bit slower in i.e. Windows Vista, as the Superfetch feature will try and cache all of the available physical RAM. This means that in the case of 3GB vs. 2GB RAM it will take longer to cache that extra 1GB RAM, resulting in longer "disk thrashing". All of this is however done at low priority I/O so you shouldn't feel the caching as very noticeable.

If you or other people need further information and clarification follow this link, which does a good job of explaining the fundamentals:

http://forum.notebookreview.com/showthread.php?t=167472

 

thanks jabbajabba, great post.

both sticks [1gb and 2gb] are ddr2, 200 pin 667, so it looks like im good there. and as far as utilizing the extra ram, im an architect and i run maya and rhino along with all of the adobe programs, and some heavy render engines...so i've been longing for more RAM for awhile.
thanks again guys for the great info.

 

I think I remember... and it's bios dependent....

You look in the bios and when you are running dual channel the memory speed indication is the full Rated ddr2 speed. If not then you will see 50% of the rated DDR2 speed.
CPU-Z will also provide an indication.

 

Thanks JabbaJabba for the clarification. My head is still stuck in the DDR days when dual channeled required two matching pair of memory.

 

i was with you spoon

 

and then there's me ...no clue what was going on..thanks jaaba

 

As was I. I remember all the fuss surrounding buying matched pairs - same speed, same capacity, same configuration. Those premium-priced pre-matched pairs were all the rage.

Thanks for the clarification, JabbaJabba.

 

Glad I could be of service. I know how the whole memory scene can be confusing. Only glad to help.

 

"Those premium-priced pre-matched pairs were all the rage."

They are still recommended by the high performance motherboard manufacturers such as Asus.

 

Alright since we're on the topic...right now I'm waiting for a 2gb stick to be delivered so I can install it on my t61p that only has 1gb. I'll be using some apps soon that require a little bit more memory that 1 gb...can I take a 512 ddr stick from my old laptop and stick it in my new one...? Or will I have some issues do you think...?

 

I have a t61p on order and I'm really finisky with my hardware. I looked at all of the various memory possibilities. Since I am a developer and run Vista, I know I could be comfortable now with Vista and 2 gb. So I examined my options. If I got two 1 gb Dimms, later I will have to discard memory to expand it.

If I got one 2 GB DIMM I've lose in memory tranfer time.

There was only one way that I wouldn't lose which was to buy 4 gb for growth. I run Vista-32 at the current time and I'm aware that my system will only want to map 3 gb. But that extra gb will be there when I decide to goto Vista-64 and I will have full memory speed.

I'm probably a poor one to give you advice, but I never compromise with the hardware and I wouldn't like myself in the morning if I stuck 2 gb in one slot and an old 512 mb Dimm in another. I don't think my front-side-bus would like me either.

 

that extra gig is known to cause problems with 32 bit vista..so there is something else to be finicky about

 

Can you expand on that?

 

^^^ I wish I could, but I just do not know enough about it. I was having turbo memory problems and one of my friends works at geek squad. He brought my notebook in to a specialist there and he said many of my turbo mem problems could be associated with the fact i have 3gb of ram, and then 1gb of turbo mem, which vista confuses as extra ram sometimes causing problems...perhaps someone else can expand on this..sorry

 

Turbo memory isn't worth the upgrade. It barely adds any performance and sometimes even makes the laptop slower. Avoid Turbo Memory if you can. Hell, avoid Vista if you can as well.

 

trust me..i know..i just wish i knew before i ordered it...i got it for like $15 extra for my configuration...but has caused so many damn problems...i almost felt like chucking my new thinkpad out the window...caused many bsod's and freezes...now i did a reinstall and didnt even install the driver...turbo mem is in there...but not being utilized and no problems since