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I know this isn't strictly a programming question, but this is still the best place I could think of to ask it.

For a long time now, I've been pondering buying a netbook, but not just any netbook. I have very specific requirements.

When the Asus EEE PC 1015pem, with the intel atom n550, came out, I almost bought it, but there was one catch. maximum 2GB of RAM, which is just a tad low considering what I need, or at least what I think I need. better to be on the safe side anyway.

So I held my breath, pondering, scheming and then suddenly, BAM, Intel released the n570, which apparently can support 4gb of ram. Saying apparently since I haven't been able to find anywhere on their site, where I can confirm the information and the processor specification isn't complete yet for some reason, but I do believe it to be true for other reasons. Among other things, this cpu will also be used in servers.

However, every single netbook manufacturer, who have put specs out for netbook sporting the n570, have included a limit of 2gb.

Now my actual question is, where in lie the limitation. Is it at all likely that it can be circumvented, assuming that the manufacturers do not change the specs?

I don't think it likely that the cpu would be the limiting factor, so what about the rest of the hardware? As far as I know, the memory controller is build in to the cpu, so that probably won't be it either. I suppose it could be a bios limitation.

What do you think?

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Mainboard and space inside the netbook.. –  halfdan Apr 18 '11 at 21:52
    
32-bit processors can only handle 4 GB max, so they probably bought a crappy motherboard that only supports 2 GB. RAM slot issue. –  tjameson Apr 18 '11 at 22:23
    
It's an interesting questions, because it could very well be that the chipset only supports 2 GB (after all, the memory controller has limits. An older example: The i815 chipset only supported 512 MB RAM, not more, and that was not a slot limitation but a hardware/chipset thing. Of course, could be arbitary to separate the markets) –  Michael Stum Apr 18 '11 at 22:26
    
@tjameson - I don't think you can argue it's 'crappy' when doing so allows you to shave a dozen millimeters off the dimensions of the machine. It's an netbook, after all! –  Shinrai Apr 18 '11 at 22:27
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@Shinrai - True. Netbooks are designed to be cheap and small, not expandable. 2 GB should be enough for mostly anybody. My 'crappy' I meant cheap. –  tjameson Apr 18 '11 at 22:31
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5 Answers

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I tried a 4G memory module, single rank which has identical pinouts (signals) as the 2G module except for chip select and clock enable (but with the same pin assignments) and it would not work. I then hardwired the chip select and clock enable lines in various configurations to guarantee activation at least half of the memory present (2 GB, like that of the 2 GB module) and that failed as well.

The ram modules have a PROM onboard that store characteristics of the memory module, like speed, latency, burst mode, etc (device parameters). Also, the absence of one additional A/D line (of the 204 pins present), say removed from the trace bus on the motherboard, is all that separates a 2 GB module from a 4 GB module, address/data buswise. Its possible to remove the trace line but that's not realistic or practical as a hardware limitation, although technically feasible.

Getting back to the PROM, the N570 CPU with its memory controller interrogates the memory module to find out what type it is and how it should configure itself to work with it. There are common (shared) bus & I/O lines used during power up that allow the CPU to do this, even though the CPU doesn't know yet which type it is working with.

If the BIOS determines that the memory at boot up is 4 GB (or greater) it may refuse to work with it, as a self imposed limitation of the BIOS design. That's why, for example, no one has got past boot up using any of the available 4 GB memory modules. This is where I believe the problem lies, not with the hardware or memory. Fix the BIOS and you should be able to handle 4 GB RAM on your netbook. Anyway that's my conclusion.

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The memory limitations are a combination of technical and licensing. DDR2 RAM generally maxed out (for typical use) at 2 GB modules. DDR3 RAM can go to 4 GB modules. It's possible the motherboard used will not support the large(r) modules - I have an Acer desktop that uses DDR2 that doesn't like all 2 GB modules. Acer openly states the system only supports 4 GB - I'm running (and typing this) with 6 GB. But I've tried going to 8 and that won't work.

If it's not a hardware limitation, it may simply be a question of what the definition of "support" is. In some cases, it's as benign as the maker not advertising the capability and not helping you with the system if you have problems (like my Acer desktop). In other cases, it's a matter of "it doesn't work" - and why it doesn't work could be any number of reasons.

The licensing aspect relates to Microsoft and how MS doesn't want to offer Windows 7 on Netbooks. Specifically, to keep netbook pricing cheap (and compete with Linux) MS has essentially decided that Windows 7 Start (sold with netbooks) will be VERY cheaply priced BUT it can only be sold on systems that come with 1 GB of RAM and max out with 2 GB and have screens no larger than 10.2". (The 2 GB max I've heard before and decided to include it here since my memory had been accurate about the Windows thing when I first started writing this).

Check out this LA Times article for more info.

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More than likely the cpu supports 2 memory slots (2 x 2gb) but netbooks only take advantage of one slot due to size restraints (and possibly agreements with Intel). Yes the bios can block or limit any hardware device if the bios code is written to do so.

ark.intel.com/Product.aspx?id=55637

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It's also probably a limitation of the RAM slot. Older slots (used on cheaper boards) only support 2 GB, whereas newer ones support 4 GB or even 8 GB. –  tjameson Apr 18 '11 at 22:32
    
All a slot is are electrical connections to the motherboard, it is a limitation of the memory controller or the bios, the memory controller says how many slots total you can have, the bios can limit how much ram each slot can use, the memory controller has the final say over all of these factors. –  Moab Apr 18 '11 at 23:02
    
As previously explained, I do not believe the memory controler to be the issue. Multiple ram slots could be an issue as netbook usually only have one, but isn't it possible to get 4gb sodim modules, and in the end, should that make a difference? I mean, it's a question of 31 or 32 bit address space (yes I know, the reality is somewhat different) who would make an effort to save one bit? –  Zacariaz Apr 19 '11 at 16:45
    
I've just talked with Intel support and, assuming they have provided valid information, the cpu it self should impose no limitations. Suppose that leaves only the mainboard, and I'm not quite sure how that can impose limitations as the memory controller is part of the cpu, the bios and the question if one ram socket is enough, if it can handle one single 4gb module and I don't see why it shouldn't be able to. Please let me know if I left anything out. –  Zacariaz Apr 19 '11 at 21:20
    
Just because the memory controller is on the same die as the processor does not mean it is part of the actual core processor(s), while Intel's statement is true, it is misleading you. Its still up to the memory controller, then the bios. –  Moab Apr 19 '11 at 22:50
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There are two sources of RAM limitations for Netbooks:

  1. Hardware: number of RAM slots and the maximum module size supported. A lot of Intel Atom based Netbooks have one slot supporting up to a 2GB module.
  2. Software: the common Windows 7 Starter Edition supports up to 2GB of RAM. A licensing limitation also limits manufacturers to only shipping with a maximum of 1GB installed.

Newer AMD C-50 based netbooks tend to support using a 4GB DDR3 1333 module but also then require an upgrade to Windows 7 Home Premium or better to make use of the extra memory. A good example are various Acer AO522 models.

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There were older units, which had 512MB of RAM soldered on-board thus a slot. Good example is MSI Wind U90 and its copies, which were able to handle 2GB SODIMM ram by means of disabling onboard RAM via BIOS, bad example is my AOA110 which is unable to handle more than 2GB, giving me total 512MB onboard + 1GB in slot (1536MB SODIMMs are a mythical entity) –  kagali-san May 26 '11 at 12:25
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I must note, that a decent amount of swap space can really solve some memory/performance problems, however, it's not a thing that is recommended to do with SSD-based models or with any kind of slow drive, anyway. Just solder in a second HDD and get your performance boost..

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