Hard Drives and Memory

If RAM is a computer’s short term memory, its hard drive is the long term memory.

Barring mechanical failure, once data is “written to disk,” it is safe until it is deliberately deleted. You can turn your computer off for days, weeks, or months and the data will still be there when you return.

This is the second article in the New Computer Series.


When casual PC shoppers talk about a new computer’s “memory,” more often than not, they are talking about the hard drive – although the memory they should be worrying about is the RAM.

Think of your hard drive as storage, not as memory.

A 500 GB drive will hold lots of stuff – but it will not speed up your computer. RAM and processor speed will have a much bigger impact on performance. If you want your computer to feel faster, add RAM. If you want to keep photos, video, and music on your PC instead of on the top shelf of your closet, get a bigger hard drive.

So does a hard drive have any effect on speed? Yes.

Computer memory, like human memory, takes many forms. Yesterday, we talked about RAM. The more RAM your computer has, the better it runs. But even if you add the maximum amount of RAM possible, eventually your computer is going to say, “Hold on – let me make a note of that,” and it will write some temporary information to disk.

This sort of short term data storage and retrieval takes place in “virtual memory,” also known as the “swap file.” If your computer’s RAM is all committed, rather than grind to a halt until you hit the “Save” button, your PC will do something very like much like plastering sticky notes all over the place.

This sticky note information will be called on as needed, moving in and out of the swap file. However, it will not be saved. Data in virtual memory – even though it was written to your hard drive – will be erased when your computer is shut down.

Writing to disk is slower than storing the same data in RAM. If your hard drive is badly fragmented, moving data in and out of the swap file will be slower still. And if you combine a slow, relatively full hard drive with inadequate RAM, you may spend a lot of time waiting for your screen to redraw or rebooting after your computer crashes.

There is one another aspect of hard drives worth considering – their speed. The disks in hard drives are moving parts. They literally spin. Most desktop hard drives spin at 7200 RPM. Older, slower hard drives spin at 5400 RPM. With a faster hard drive, applications will open more quickly.


For best performance – get as much RAM as you can. Add a bigger hard drive if you plan to take lots of photos or video. And look for a drive with a rating similar to this: 500GB Serial ATA Hard Drive (7200RPM)

Next Up in Part 3: What are all those other numbers about? CPUs, Bus Speeds, and Cache