The answers to many of the most common questions I’m asked about computers can become much clearer with a quick description of how a computer actually works. I don’t want to turn this into an encyclopedic breakdown of every part in a computer, but I want to provide an approximated, simplified explanation of what each major component does, and how it interacts with the rest to accomplish the end results displayed on your screen.

When you buy a new computer, there are typically three important specifications to consider; hard drive size, CPU speed, and amount of RAM.

Your hard drive is the physical spinning disk that’s housed somewhere in your computer. If you place your hand on your computer as it’s starting up or working hard, the whirring or vibration you feel is probably the hard drive.  It’s much higher-capacity than any CD or DVD, but it’s fairly comparable in its function. It houses all the data on your entire computer, which is coded to this physical spinning disk with billions of little positive and negatively etched pits in its surface. This is why you NEVER put anything highly magnetic too close to your computer, because it will make the previously encoded data all uniform and any information on that section of the hard drive will be deleted.

Hard drive space is often confused with RAM (acronym for Random Access Memory), but both of them store data, just using completely different methods, for different purposes. RAM, unlike a hard drive, is solid-state memory. This means that it doesn’t rely on tiny magnetic readers to process information, but can access the transistors that store the data immediately and simultaneously. It doesn’t need to spin that disk around and locate the information it’s looking for, it can simply access it directly to feed it to whatever function is asking for it. If you own any modern iPod/iPhone/iPad (with the exception of the iPod classic) all of the memory in that device is also solid-state. Solid-state memory is faster, more durable, and uses less battery power than a normal hard drive, but it’s much more expensive.

So why does your computer need both RAM and hard drive space? Because they both have different strengths and shortcomings. Your hard drive can certainly store lots of data, but it can’t access all of it very quickly. RAM is exactly the opposite; it’s instantly accessible, but it’s not very high-capacity. So RAM temporarily caches any information that the hard drive has been accessing, or may need to access, before it feeds it through the processor. This makes for much faster performance if the same information needs to be accessed again.

The CPU (central processing unit) is the computer chip that actually interprets all the information being sent to it from the hard drive, through the RAM. The information can be present, moving through the hard drive and RAM, but the decisions about how the information is presented, and how the computer user interacts with it, are entirely up to the processor.

Getting back to my initial statement: those three most important numbers to know about your computer are hard drive size, amount of RAM, and processor speed. My favorite analogy for this whole system: If we can think of a computer as a highway for very small, very fast cars that carry information, these separate components can be thought of as follows- hard drive space equates to the total number of cars on the road. RAM is comparable to the number of lanes on the highway. And CPU speed is analogous to the maximum speed limit for any individual process.

To visually see this on a mac, go into your Macintosh HD/Applications/Utilites/Activity Monitor. Toward the bottom of the screen there are several different sections you can click through; these show you how hard each of these components are individually working.