What is the difference between a hard drive and memory of a computer

When I worked as a software support engineer, I noticed that many people had a difficulty understanding the difference between a hard drive and memory. I tried many different metaphors. Let me share the one that stuck with me even 25 years later

The hard drive of your computer is like the library in your study (bedroom):

The bigger it is, the more books and videos and even music it can store.And if it’s really big, it’s even possible you will buy (& store) some books twice.

The memory is the desk you are working on:

If you have a small desk, you can open one book at the time. When you want to read or consult another book, you first have to close the current book, put it back into the library. Only then you can pick another book and read it.

The same is true for your computer. If your memory (desk) is full, the computer will swap out the program you are working on and will load the new program.
Now as a computer is smart, it will reserve part of the harddrive (library), to temporarily store the programs you think are still open. That is the pile of books you put on the side of your desk, when you research for that one project you are working on. The books are closed, yet they are also close by and thus quick and easy to find.

It’s very important to understand the difference for when a computer is short on one of these.

I have friends that will delete all kinds of files from their computer, because they are short on memory. That’s like throwing books away, because your desk is too small to open that large atlas. This won’t help.

Also upgrading your memory because your hard drive is full, is like buying a bigger desk, because your library can’t store all the books you need. Hence also useless.
Usually harddrives were physical disks that turned around at an enormous speed to read and write the data. And “memory” (or RAM – random access memory) were chips that could read data faster. (And lost that data when the computer lost its power)

Other kind of storing devices

  • Floppy disks:  portable deviceS that you can insert in your computer to read and write small portions of data.
  • CD: a disc that at first could only read data, yet later they also made writable CDs. So you could write these disks, (usually only once)
  • We also have USB sticks, a small device that you plug into a computer and to store data. The technology used for these devices was also a memory chip, yet these chips did not lose their data when disconnected from a computer.
  • SDD harddrives: the same chips now inside a computer. They share part of the name with the hard drive, because they share the same purpose: store data inside a computer. Yet they work totally different (aka working with chips and not drives)

When you compare an SSD hard drives, to the fastest “normal” hard drive, they are extremely fast.  And even more important, they don’t risk screwing up writing when you bump your computer.

Which means this kind of hard drive technology works also well for portable phones.
To add to the confusion, in mobile phones, we call the SSD harddrives “memory”. When people talk about the capacity of their phone, they generally talk about the hard drive, how much can the phone store. For most phones it’s hard to find what is the actual memory used.

The Cloud

These days we also store a lot of data in the cloud. Both icloud, google drive, oneDrive and Dropbox, give you the option to store more files than you phone can store, and share that with your computer. By default these tools are configured to upload files to the cloud and download them when you need them. In essence, the cloud is a really big hard drive that someone else owns. In our analogy,  that’s the public library: it stores an enormous amount of books, yet these books are a lot farther away from your desk.

I personally like to work offline and sync to the internet when connected. As far as I know, all these tools allow that. You can compare that to people who prefer to buy their favourite books, instead of needed to go to the library to read them again.

In both cases the disadvantage is that you need a lot of place to store data/books. Yet once you have that place, you have everything with you, all the time. Especially handy when travelling and hoping in and out trains and planes, You don’t need to turn on roaming to have acces to your own files.

So next time someone mixes up memory and hard drive, talk with them about their desk and their library.