Why Vista needs 4GB of RAM

How big a penalty? For starters, it will take much longer to load up that game. A typical Call of Duty 4 level load time jumps from under 10 seconds on an otherwise well-specified PC to more than a minute and a half in heavy multi- tasking conditions. If that sounds bad enough, it gets even worse if you decide to Alt-Tab out of the game and go back to the desktop temporarily, perhaps to respond to an IM or send a quick email.

Fails to break four minutes

In our testing with a powerful quad-core PC running 2GB, it takes well over four minutes for application windows on the desktop to become fully responsive following such a manoeuvre. That's an excruciatingly long time. Indeed, not only is the process inordinately time-consuming, but the limited memory availability can lead to system instability and even crashes. In short, with 2GB of memory, it's not a realistic option.

So, what happens if you slam in a little more RAM? With 4GB installed, be it Vista 32-bit or Vista 64-bit, it transpires that game level load times are totally unaffected. To be more specific, our test involves approximately 20 multi-megabyte image files open in Photoshop, several PDF documents open and as many media-rich, flash-animated webpages on the go as you can shake a DDR2 DIMM at. But even with the slight loss of address space due to memory mapping, there's enough to contain most if not all of that as well as the whole of Call of Duty 4.

As for hopping back to the desktop, it's likewise a much, much less painful experience. You can expect to enjoy fully responsive access to the desktop and applications in less than 30 seconds.

Buena Vista

Things get even better with the full access to all 4GB that Vista 64-bit delivers. In common with Vista 32-bit, game level load times are unaffected. But there's a really impressive bit. When you Alt-Tab back to the desktop from Call of Duty 4 – it is essentially instant – just the few seconds required by Vista to re-enable the 3D Aero interface is all that is required.

The explanation for this monumental difference in multi-tasking performance is actually pretty straightforward. With 2GB installed, there simply isn't enough RAM to store all that application data. A Windows operating system must therefore take a snapshot of the state of each application and cache it on the hard disk before proceeding to load the game data into RAM. Alt-Tab out of the game and you get the opposite process. The game state is saved to disk before retrieving the original desktop application data.

It's a process that's usually known as disk swapping and it will bring any PC – no matter how powerful – to a juddering, grinding halt. But why is it so much more prevalent in Vista? Mainly because Vista soaks up much more memory simply to sit in an idle state.

Clean boots at a cost

Inspect Task Manager following a clean boot of a freshly installed copy of Vista and you discover something pretty shocking. At least 700MB will have been snaffled up just to keep Microsoft's lumbering colossus alive and doing nothing of any note. On a 2GB rig, that leaves you with a little over 1GB of memory. In this brave new age of embedded video, multi-megapixel amateur photography and ubiquitous HD displays, that really isn't enough.

In multi-tasking terms, therefore, having a large amount of RAM to hand fundamentally changes the way you can use your PC without incurring a performance penalty. You no longer have to worry whether opening up a few more webpages, documents or images is going to spark off a brick-chewing cacophony from your hard drive and bring performance to a standstill. So, you can happily multi-task with almost infinite impunity and take that treacley, recalcitrant hard drive largely out of the equation altogether.