Q. I understand Windows Vista will only recognize and use 4 gigabytes of RAM. Is this true? My motherboard will hold 8GB. But I don't want to buy too much RAM.

A. We have reached a junction of old and new in operating systems. I'm referring to the glacial ascent of 64-bit systems. This is confusing many people.

Lots of people have built tricked-out, 4GB systems. They soon discover that much of their RAM is unusable.

These are 32-bit systems. It sounds like you have a 64-bit motherboard. So you can use a lot more RAM. However, you'd probably be wasting your money.

Let me explain how this works.

For those who don't know, a bit is a 1 or 0. Eight bits equal one byte. Sixty-four-bit systems can process data in 64-bit chunks. Theoretically, that makes them twice as fast as more common 32-bit systems.

Today's 64-bit microprocessors have been sold for consumers since 2003. They are the latest in a progression dating to the 1970s. Over time, computers have used 4-, 8-, 16-, 32- and now 64-bit systems. Nearly all consumer chips are 64-bit today. But software has been slow to catch up. Most software is still 32-bit.

Consumer computers have used 32-bit systems since the mid-80s. Until recently, almost all computers in stores were 32-bit. That is changing, leaving many consumers' heads spinning.