Hardware & Infrastructure
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6/16/2006
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How To Remotely Monitor Memory Usage

Adding extra RAM when your machine doesn't really need it is pointless. Here's how to tell when it's time.

Optimizing PC memory isn’t as easy as "just add more," and in fact there are plenty of times when adding more RAM is downright pointless. This column will cover some monitoring tools and techniques that will help you figure out what's really going on with your machine and when you do need to add more RAM.

We’ve all heard the mantra a thousand times: adding RAM is the easiest and most reliable way to boost the performance of a sagging system. And while that’s usually true, there’s a lot that goes unsaid in that homily.

For one thing, it isn’t always easy to tell when you are truly running low on memory. Although Windows provides lots of information about memory utilization in various places, it still manages to obfuscate most of what you really need to know. This occurs because Windows either overloads the administrator with irrelevant information, or it hides the information that you really need in an out-of-way location.

UNIX isn’t much better. The free utility that comes with UNIX-based systems usually only provides summary data, and you have to dig around in unusual places to find actionable utilization figures. As a result, administrators have a hard time conducting the kind of ongoing clinical observation that leads to true understanding of memory utilization. So most of us just salute the platitude and dump in more memory, whether it's actually needed or not.

As one example of this phenomenon, the SUSE Linux system that I use for my public Web and e-mail server originally only had 512 MB of RAM. This should have been more than adequate for the lightweight load that I was expecting, but the system tools showed that the box was constantly running low on memory. And even after I bumped it up to a full gigabyte, the system still complained.

I had just gotten ready to add another gigabyte when I discovered that most of the memory was actually being consumed by SUSE’s aggressive disk-caching algorithm. Every time I added more memory, the operating system drank it up for the disk cache. In reality I was nowhere near hitting any kind of memory limit for the applications themselves, even with just 512 MB.

Windows has some behavioral oddities about the way it handles memory too. For instance, Windows XP is supposed to be able to handle up to 4 GB of RAM directly, but sometimes it can only read 3.12 GB. Meanwhile, 32-bit Windows applications have access to only two of those gigabytes by default.

Programmers have to use special APIs to make their applications access more than that (see Microsoft's KB article 888137 for more information). Without some significant tweaking by all involved parties, additional RAM beyond these built-in ceilings simply won’t help.

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