Ask the typical PC expert "how much memory do I need?" and they'll probably tell you to "get 4GB, it's very cheap these days and you're short-changing yourself with anything less".

And this isn't an unreasonable answer. The less RAM you have, the more likely Windows will have to start swapping out pages of memory to your hard drive, drastically cutting your system's performance.

And if you only need the most basic DDR2 memory then adding 2GB to a PC could cost you under £30 online, even including postage and packing.

If your system requires the latest DDR3 RAM, though, you may have to pay more than twice that amount. Which is starting to become a sizeable figure, especially if you're short on cash right now. And worse still, limitations in 32-bit Windows mean your system will probably only see maybe 3.1GB of the 4GB memory you've paid for.

So it is absolutely essential that you install 4GB of RAM? If you're short on cash, how much - or how little - do you actually need? We've taken a closer look.

How much RAM do I need for Windows Vista?

Microsoft claims that Windows Vista can run with a minimum of 512MB of RAM for the Home Basic edition, 1GB for everything else.

And this is true. We tried it with Windows Vista Home Premium, and the system and a few basic background programs took around half our 1GB, leaving the rest free for whatever we wanted to do.

The problem, of course, is that's not very much. If you only want to browse email, use the web, listen to music or run simple apps then 1GB would just about be enough. 2GB will give you a great deal more room to manoeuvre, though, allowing you to play basic games, watch videos, edit photos, and that's what we'd recommend as a sensible minimum for Vista.

How much RAM do I need for Windows 7?

Microsoft says that 32-bit Windows 7 requires 1GB of RAM at a minimum, rising to 2GB if you've opted for the 64-bit version.

This is marginally more realistic than their Vista figure, as Windows 7 has been optimised to make better use of memory. And so if you're currently running Vista then you should be able to migrate to Windows 7 without requiring any additional RAM (you'll probably find your system performs better, too).

Otherwise, the same rule applies as with Vista. The 1GB (32-bit)/ 2GB (64-bit) Microsoft recommendation is sufficient if you're running only very simple programs. But if you want to do anything more complex, or like to run several apps at the same time, then we'd recommend you install at least twice that amount to deliver reasonable performance.

And if you're in any doubt, perhaps you run a program that seems complex but you're not sure how much RAM it requires, then check at the author's website to find out more. There's usually a "system requirements" section, perhaps on the download page, that will report the minimum amount of memory that the author recommends you should have.

How much RAM do I need for gaming?

Games make heavy demands on your graphics card, hard drive, and CPU. But, surprisingly, they don't always need a great deal of RAM.

To illustrate the point, we browsed down the current best sellers and checked the back of the box to see what they required. And discovered that while basic games like the Sims 3 requested a minimum 1GB RAM on an XP system, 1.5GB on Vista or later, just about everything else - Mafia II, R.U.S.E., Battlefield Bad Company 2, Mass Effect 2, Pro Evolution Soccer 2011 and more all recommended 2GB RAM.

Part of this is due to marketing. No-one wants to say that their games require 4GB of memory, of course - they don't want to put people off buying them.

It does show that you stand at least a chance of running even the latest games on a 2GB RAM system, though, so that's what we'd recommend as our absolute minimum.

And if you've only 1GB, don't feel left out, just look for older games. 2004 hit Doom 3, for instance, requires only 384MB, and should run happily on just about any system.

How much RAM do I need for WoW?

Many games require less RAM for Windows XP than Vista, or Windows 7, and World of Warcraft: Wrath of the Lich King is no exception. Right now XP users need a minimum of 512MB, while 1GB is recommended; if you have Windows Vista or 7 then you'll need 1GB minimum, 2GB recommended. Check out the details.

How much RAM do I need for video editing?

Video editing is a very complex process that will test every part of your system. However, much like gaming, it don't necessarily require enormous amounts of RAM.

Adobe Premiere Elements 8, for instance, requests a minimum of 512MB on XP systems, 1GB on Vista or Windows 7, with 2GB necessary in both instances if you're looking to edit high definition content (AVCHD or Blu-ray, for instance). And it's a similar story with Sony Vegas Movie Studio HD Platinum, Nero Multimedia Suite 10 and other editors: most wanted at least 1GB, or 2GB for high definition editing.

Of course, as usual, these are the minimum figures, and you'll probably get considerably better performance if you add more memory. But if you're happy to wait, than 1GB of RAM will allow very basic editing abilities, while 2GB should let you work with just about anything.

How much RAM do I need for my laptop?

If you're only running basic apps on your laptop then you may be able to get away with the minimum amount of RAM required by your operating system (see above).

However, some older laptops in particular don't have any graphics memory, and use system RAM instead: not a great deal, but if you're very little anyway then it could still cause you problems.

And don't forget, if you have too little RAM and Windows is always shuttling memory pages to your hard drive and back, then this will have an effect on your battery life. So on balance we'd prefer to have a decent amount of RAM in a laptop, 2GB at a minimum.

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