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Buying a notebook computer can be an exercise in limitless possibilities, whether you're buying for yourself or for 250 users in your organization. That's because most laptop vendors offer a dizzying array of configurations.

Some people simplify matters by overspending, wagering that loading the laptop with unnecessary power is better than getting shortchanged on performance. Others underspend, assuming that it's better to save money than to pay for unneeded power.

Such uninformed decision-making, however, often leads to either underpowered or overpriced laptops. But who has time to test the major configuration choices to find out which offers the best balance of performance, price and battery life?

Well, I did.

To find today's notebook configuration sweet spot, I used a typical laptop to examine performance with six different levels of system memory, ranging from 512MB to 4GB. I also examined whether to use a traditional hard-disk drive (HDD) or a solid-state storage device (SSD) that uses flash memory.

I looked at the impact of these choices on both system performance and battery life. (See "How we tested" for details.)

Along the way, I learned several things about the trade-offs between performance, battery life and price. Here's what I discovered.

How Much RAM Is Enough?

The first part of the laptop configuration conundrum is how much RAM to add to use. My tests found, not surprisingly, that adding more RAM leads to better performance. However, I also found the point at which adding RAM stops being cost effective and actually eats into the system's battery life.

Adding RAM is effective because it enables more of the system's operations to be done in the notebook's system memory. That, in turn, means less reliance on slower virtual memory, which uses the laptop's physical storage to simulate RAM when there is more data than the regular RAM can handle.

In my tests, filling the memory slots with 4GB increased memory performance -- how long it takes for data to go in and out of memory -- by about 7% and increased overall system performance by 15% compared with the test laptop's base configuration.

The biggest improvement, from a percentage point of view, occurred when increasing memory from 512MB to 1GB, but there was also a significant increase between 1GB and 1.5GB.

However, upgrading memory is effective only up to a point. That's because at some point the added memory isn't needed, and as a result, it sits idle and doesn't help with performance. That unneeded RAM does, however, draw power from the laptop's battery.

Benchmark tests on our test Windows XP laptop found the cutoff point to be at about 1.5GB of RAM. After that, adding more RAM resulted in smaller and smaller performance boosts.

In fact, the last gigabyte of RAM added, which brought the total to 4GB, increased overall performance by less than 1% and lowered battery life by 15 minutes. Most people will not find this to be an acceptable trade-off.

These tests were run on a Windows XP machine. (Read more about why I used a Windows XP laptop in "How we tested.") Given the higher resource demands of Windows Vista, it is reasonable to assume that the peak benefit in terms of adding RAM to a Vista system would occur at about 2GB.