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I'm having a hard time figuring out whether or not a certain laptop/computer's RAM can be upgraded or not. Is there a rule of thumb that determines how much max RAM one could add to a system without looking it up via external websites?

A little bit of a background information: I work in computer sales at a computer electronics store, so it is virtually impossible for me to install any sort of software that would detect computer specs, and I get a lot of customers who wonder what laptop/desktop RAM upgrades usually are. It's frustratingly annoying to have to constantly search the web for information.

Is there a certain rule that adding more RAM entails? Does it make a difference if it's a 32-bit or 64-bit machine? Are other factors, such as the OS, hardware, and other things matter?

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up vote 4 down vote accepted

There is no easy way to find the maximum amount you can upgrade the RAM to without doing some reading of manuals, opening the computer or using some hardware reporting software.

There are many limiting factors on how much RAM you can install and use. Main ones are:

Motherboard: Physically, the number of free RAM slots Logically, the ability of the BIOS and memory controller to detect and address your RAM

Operating system: Windows 7 has imposed artificial limits

  • Starter: 2GB (32bit only)
  • Home Basic: 8GB
  • Home Premium: 16GB
  • Professional: 192GB
  • Enterprise: 192GB
  • Ultimate: 192GB

Linux doesn't have these sort of arbitrary restrictions.

There is no easier way to tell the maximum type, configuration and amount of RAM that the motherboard will accept without looking up the specifications in the manual.

You can however say that if they are running a 32bit OS and have 4GB of RAM, that they cannot upgrade further without at least first upgrading their OS.

That said, in Linux you can query the BIOS directly. It's not 100% accurate (e.g. BIOS might report that it supports 4 DIMM slots but your board may only physically have 2) but will give you a rough idea.

As root, run:

# dmidecode -t memory
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What's the reasoning behind the 32-bit OS with a limitation of 4GB? – cyberweb poweruser Nov 3 '13 at 17:04
@Retrosaur A 32-bit OS cannot use more than 4GB of RAM, so adding more is useless, even if the hardware supports it. There are exceptions (PAE), but it doen't apply to most consumers running Windows. – mtone Nov 3 '13 at 18:09
@Retrosaur A 32bit address can only point to 2^32 (= 4294967296) unique addresses, which works out to be 4GB. – jabolotai Nov 4 '13 at 4:09

I know you asked no external websites, but I found that fastest way to find out actual limit for max memory is Crucial Memory Advisor.

It does not require to run any detection software, but you need to provide PC or motherboard manufacturer and model.

What I really like about it that it often shows system limits better than original manufacturer documentation does. For example, HP documentation and website claimed that my old HP laptop only supported up to 2GB RAM. But, according to Crucial, limit was 4GB. I have purchased upgrade memory and installed it into that laptop, and it worked just fine.

As for 32-bit vs 64-bit - as long as computer is not older than 2-3 years, it should support 64-bit, and there is no reason to run 32-bit OS these days. If you still need to run 32-bit, often it does not make any sense to install more than 4GB of RAM (in reality, 32 bit computer will not use more than 3 to 3.5 GB, depending on BIOS). Linux can use more than 4GB in 32-bit mode with PAE, but it simply does not make any sense if you can run 64-bit.

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I believe the previous answers address only a small part of the problem.

First, there is the issue of hardware. It does us no good to know that we have an OS capable of using up to 192GB, if the expansion slots can only accommodate an extra 4GB, for instance. So here the issue is: how do I know how much more memory can I physically add?

Here the answer can only be: you will have to look it up. It is essentially a matter which every producer (Dell, Acer, Lenovo, Sony, Toshiba,...) addresses on the basis of (among other things) marketing strategies (is this pc going to be top of the line? basic product? intermediate?). Reasonable rules of thumb are that desktops will have larger and more expandable RAMs than laptops (big surprise...), that it is uncommon to find laptops exceeding 8GB (but some do exist), that typical gaming pcs have of order 32GB, but there are so many exceptions that the value of these rules of thumb is limited at best.

The second reason why previous answers were incomplete is that they only address Windows pcs, while of course there are Macs as well. Here the situation is much simpler because of the smaller number of models to which this question applies. You can find the complete list of maximum amount of RAM for each Apple product since G3 here. The list is however still sufficiently long that it is impractical to reproduce it here. But let me just say it is very complete.

The third reason why the previous answers were incomplete is that, even from the point of view of software, the maximum amount of RAM that an OS can use depends on the OS. For instance, let me give you the limits of the Linux Kernel:

32 Bit - 4GiB RAM

32 Bit + PAE (Physical Address Extension) - 64GiB RAM

64 Bit - 2^32 GiB ~ 4 billion GiBs.

As you can see, there are here two major differences with respect to Windows. On the one hand, there is an important modification of the 32-bit kernels (PAE) which allows even these to take advantage of amounts of RAM exceeding the (naive) theoretical limit of 4GB for 32bit machines. On the other hand, there is a huge limit to the amount of addressable RAM for the 64bit version, that makes it suitable even for the largest machines currently available: Titan has 693.6 TiB of RAM spread out across 18,688 nodes (GPU RAM accounts for about 1/6th of that). This incidentally, jibes with the fact that all supercomputers (except 1) use OSes of the *Nix family (see the statistics here).

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+1 This really shed some light on me for both MacOS + Linux based systems. My thanks – cyberweb poweruser Nov 3 '13 at 17:12

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