Should I get a dual core or a quad core processor?

A "core" is simply another way of saying CPU or, in a sense, computer.

The CPU or Central Processing Unit is the computer. It's the thing that executes instructions, one at a time, very quickly to make the system "do stuff". Everything else - the memory, the circuitry on the motherboard, even the hard disk and other peripherals, are there either to support the CPU in its task, or to allow the CPU to interface with devices or people.

A single core CPU can do exactly and only one thing at a time. It does them very quickly, so it can switch between different things to make it look like it's doing several things at once, but in fact at the core of the matter (pun somewhat intended), it's doing exactly one thing at a time.

A dual core machine can do two things at a time.

A quad core machine can do four things at a time.

The math is pretty easy there.

To understand if there's any benefit to single, dual or quad core for you, we have to understand how you use your computer, and if any of the things you use it for are actually "CPU intensive". Many, if not most, of the things you've mentioned like word processing, internet surfing, and even malware scanners are not CPU intensive. They're held back by the speed of other things: a word processor is only as fast as you are, surfing the internet is limited by the speed of your internet connection, and even things like malware scanners are usually limited by the speed of your hard disk. In almost all cases your CPU, even a single one, is much faster than needed for any of these.

So why have more than one core?

The most obvious reason why you would need more than one core is when you are doing things that are CPU intensive. But even then things get tricky.

File compression or audio and video encoding are good examples of processes that are very computationally intense. In other words, when compressing a file, the process to calculate the compression is typically slower than reading and writing the file being compressed. One would think it would be twice as fast on a dual core, and four times as fast on a quad. Unfortunately, most of the time it's no faster.

The reason is that software must be written to take advantage of multiple processors, and most software is not. (Writing what's called "multi-threaded" software can actually be quite complex - I know, I've done it. ).

Most software is either not CPU intensive, or is written assuming there's only a single processor.

What that means is that if you run that file compression and watch your CPU usage, you'll find that exactly one of your two or four cores is completely consumed by the compression operation, while the other(s) are mostly idle.

On the other hand, some software - often video or audio processing software - is often architected to use multiple cores.

With that as a lot of background, what's my recommendation?

I will now get at least dual core machines, even for machines that are never intentionally going to be running CPU intensive software. The reason is simple: if something hangs or a program crashes in such a way that it is eating up all CPU resources, it's doing so on only one of the two cores. The other CPU core is left running available for other tasks - like handling the screen and keyboard - and the machine remains usable.

If a quad core processor were the same price as a dual core, I'd certainly say go for it. There's no real downside to having more cores, but typically a quad will be more expensive, often by a significant amount.

If, on the other hand, you plan to run CPU intensive software that you know will use multiple cores if available, or you plan to run several CPU intensive programs at the same time, then perhaps a quad core machine might make more sense. My desktop machine, in fact, has a quad core CPU specifically because of my plans to do some video editing and CPU-intensive rendering.

But for most people: dual core is plenty.