asymmetric RAM memory on X61 tablet

[fox_napier]

Hello all,

On a X61 tablet, due to the Santa Rosa platform I believe 4 GB of RAM memory is supported. However, due 32 bit Vista Business can only address ~3GB of this RAM (64 bit Vista editions can work with the entire 4 GB.).

I am having difficulty finding a 2 GB RAM module as Crucial.com only has 2 1 GB kits available (http://www.crucial.com/store/mpartspecs ... E1A5CA7304) . Anyone know where to get such a 2 GB RAM single module?

Also, someone posted about the performance hit due to the asymmetric modules in the two RAM banks, with 1 GB in one bank and 2 GB in the other. From what I can recall, it has something to do with DDR2 memory not being able to work in double data rate mode. However, forum searches have come up empty so please repost or indicate link.

Is this a significant performance hit? Should I just go with a 1 GB RAM module for this empty bank for 32 bit Vista Business on a X61 tablet?

[qviri]

Also, someone posted about the performance hit due to the asymmetric modules in the two RAM banks, with 1 GB in one bank and 2 GB in the other. From what I can recall, it has something to do with DDR2 memory not being able to work in double data rate mode. However, forum searches have come up empty so please repost or indicate link.

This is not exactly the case. All DDR2 runs at "double data rate" (that's what the DDR stands for) compared to the system FSB. The DDR2-667 you linked to runs at 2*333 MHz FSB. The rate indicates the speed at which the RAM can transfer data.

As a bonus to that, if you have matching memory (usually a matter of getting the same model, but sometimes you have to match the revision or date of manufacture - which is why the "kits" are sold), it's capable of running in "dual channel". This doubles the bandwidth as opposed to speed. Since most applications access smaller chunks of memory sequentially, as opposed to accessing massive amounts of RAM at the same time, dual channel usually does not give much of a performance boost.

It's kind of like widening the highway as opposed to raising the speed limit. If you're a packet of data driving down the highway, you usually benefit from higher speed more than from the extra lanes, unless there's a lot of other packets driving next to you.

Is this a significant performance hit?

No.

[SFWrtr]

Try this link for a 4GB 2x2GB kit at Crucial.

http://www.crucial.com/store/listparts. ... l+Types%29

Since their automation doesn't offer "X61 tablet" in the list box, yet, I assume you picked "X60 tablet" instead. That's what this link is based on. Since there is no difference in the memory specs for the X60 and the X61 tablet (the Santa Rosa FSB 800 does not extend outside to the memory bus), I think this is a safe bet. Or you can wait until Crucial updates their site...

[ryan18]

On a X61 tablet, due to the Santa Rosa platform I believe 4 GB of RAM memory is supported. However, due 32 bit Vista Business can only address ~3GB of this RAM (64 bit Vista editions can work with the entire 4 GB.).

Can anyone cofirm that 32 bit Vista Business can only address ~3GB of RAM? This would seem to be an OS limitation as 2^32 = ~4GB.

I read somewhere that it can use 4GB and by default it is set to 2GB user and 2GB kernal but there is a jumper on that can be switched to change that to 3GB user and 1GB kernal.

[SFWrtr]

The 2GB + 2GB limit was an earlier limitation and doesn't apply. It was probably Win 9x. Sorry, but I don't remember the details, though....

Re: The ~3GB limit: Lenovo states this exists in the product literature. Microsoft even states it on their web site. It is an OS architectural thing, where the address lines are used for mapped I/O. It dates back to when MBs where hugely expensive. I mean, when 4MB machines were considered BIG, who'd ever really consider 1GB let alone 4GB? (If you look, I think you will find other threads about the 3GB limit on this site...)

Myself, I got the 2x2G kit. In the near furture, when it seems that Lenovo fully supports 64-bit Vista (with all the drivers and utilities), I'll upgrade to 64-bit and recover the dormant space.

Too bad Lenovo didn't have the 64-bit setup ready at launch! I'd rather have gotten it preconfigured!

[ryan18]

thanks for the reply. thats unfortunate that microsoft only allows you to use 3GB. i still might go for 4GB myself for the reason you stated as well as the fact that i am going to be setting up a dual boot system with Linux which will be able to use the 4GB even though i will have no real need for 4GB of RAM in Linux but oh well.

[fox_napier]

Thanks to all for the informative replies. Note that 4 GB RAM on an ultraportable laptop may be deemed excessive for the average user but there may be uses for it as well as some future proofing.

If there is little performance hit with the asymmetry, and given the cost of a single 2 GB module ($184.99) vs. a single 1 GB module ($43.99), it may be worthwhile to go with the latter. I only have one bank free, since one bank is already occupied with a 1 GB module.

I did some further reading on the 4 GB limit and I am not sure whether its only OS dependent and whether some of it can be overcome with the PAE switch in Vista. These webpages indicate that the hardware chipset on your computer also influences how much of the memory the rest of the hardware, such as CPU, and software, whether it is some flavor of Windows or Linux, sees:


http://www.codinghorror.com/blog/archives/000811.html
http://www.dansdata.com/askdan00015.htm
http://support.microsoft.com/kb/929605/en-us
http://www.start64.com/index.php?option ... Itemid=114
http://www.nabble.com/Kernel-only-see-3 ... 63664.html


and this webpage indicates that the PAE switch provides a partial, but not total, resolution to accessing the memory:

http://support.microsoft.com/kb/929580

thanks for the reply. thats unfortunate that microsoft only allows you to use 3GB. i still might go for 4GB myself for the reason you stated as well as the fact that i am going to be setting up a dual boot system with Linux which will be able to use the 4GB even though i will have no real need for 4GB of RAM in Linux but oh well.

[SFWrtr]

...4 GB RAM on an ultraportable laptop may be deemed excessive for the average user but there may be uses for it as well as some future proofing.

Don't sell this unit short. I'm using Photoshop and video editing software on a machine that has 1/3 the horsepower of the X61 and it performs well. High-spec gaming is about all that is really not good on the machine.

...If there is little performance hit with the asymmetry, and given the cost of a single 2 GB module ($184.99) vs. a single 1 GB module ($43.99), it may be worthwhile to go with the latter. I only have one bank free, since one bank is already occupied with a 1 GB module.

If you don't mind throwing away this newly purchased 1GB module when you eventually upgrade to 4GB, that makes sense since you already got the 1GB installed. 2GB is supposed to be the sweet spot for these Vista machines. If you run memory hogs like Photoshop, 3+GBs when 4GBs installed would be worth it. Myself, I ordered only 512MB installed and I saved $55 to apply toward my 4GB.

Prices will generally continue to go down unless something radically increases the demand for RAM. According to my industry insider, 2GB units will probably come down to a price of a bit more than 2 times the 1GB units. Since there seems to be a drop of about $20-$40 dollars every 2-3 weeks, this may not be long in coming.

BTW, thanks for the links. I knew about the PAE, but not that it was MS sanctioned. I'll try that when I get my x61T.