Have you ever imagined how your computer stores all of your documents, photos, music, videos, games, and various other software?

All of your files are stored in the memory of data storage devices. You might have heard about Hard-Disk Drives (or HDDs) and the new up-and-coming technology of Solid-State Drives (or SSDs). These are collectively known as “storage technologies” and these types of memory storage devices will be the main focus of this article. But before we dive into them more, we need to talk about the other kind of memory.


The RAM in your computers is also a memory device, but this serves a different purpose – which causes great confusion: Random Access Memory (or RAM) is a series of chips which are used by a computer during start-up. Also any running program or open files are also stored in RAM. The main difference is that if your computer loses power for any reason, all information stored in RAM will be lost. On the other hand, data on the hard drive will be stored continuously, even if it is not powered by an adapter.

The upside of RAM is that the computer can access this magnetic memory instantly, while a hard drive memory is much slower. In fact, any file you access on the hard drive memory will first be located and then transferred to the RAM before it can be used.

It is not a great analogy, but you can think of your hard drives as your long-term memory and your RAM as your short-term memory. You can instantly remember what happened a second ago, but you may need to think for a while before you can remember where you were at your 18th birthday, though the moment you remember it, it will now be in your “RAM” and you can talk about what happened very easily and quickly.

Both RAM and HDD/SSD devices can get full: If you have too many programs installed and/or if you have too many files/folders, then your HDD/SSD might get full. In this case, you have to uninstall some of your programs and/or delete some for your files/folders. When your RAM gets full, on the other hand, it means that your computer does not have enough “short-term memory” to continue the operations at hand. This means that you have too many browsers, software, programs running at the same time, so closing some of these will release the RAM space you need to keep running your computer smoothly.

Now that this is out of our way, we can take a better look at the long-term memory solutions such as HDDs and SSDs.

What is Inside an Hard Disk Drive?

Imagine a disk in your hand that stores data. A Hard-Disk Drive contains several of these disks spinning at high speeds which cumulate to be able to store huge amounts of data. In other words, the disk spins for the HDD head can access different parts of the data, read them, and recreate the file/folder you are trying to open/access using this data.

The mechanism which is used to read or write data from a disk is very similar to a record player. Imagine the components of a vintage record player.

  • A phonographic needle arm reads the grooves on the vinyl
  • A Vinyl that contains grooves that translate to music
  • Speakers who process the signals coming from the needle arm

Now compare this with a hard disk, a mechanical arm also known as the recording head is similar to the phonographic needle that operates magnetically over a disk similar to vinyl and the computer is the speaker in this case, processing the data.

How Does a Hard Disk Work?

Every individual disk in the modern hard drive is spinning at a very high speed. Hard drives have been engineered with spinning rates as low as 1,200 RPM and as high as 15,000 RPM. But today, most laptop and desktop hard drives have speeds between 5,400 and 7,200 RPM.

Each of these hard disks has an electro-magnetized mechanical arm, which runs over the disk to read and write data. The data is stored in a memory cell called a “bit“, by recording it in the microscopic grains as a magnetic pattern as either a 1 or a 0.

Something like this:

This bit is the smallest unit of memory. 8 bits of memory make up 1 byte. So, your 1 Terabyte Hard Drive contains 8,000,000,000 bits. That’s a lot of data!

These bits are very densely packed on the surface of the disk. A modern hard drive can pack up to 600 Gigabytes per square inch! That is insane! This is why your hard drive can potentially store more data than your library can!

Why Does Drive Memory Gets Corrupted?

Imagine this as some data stored on your Hard Drive:

These individual bits add up to a cluster which can represent a file or a photo. Bits can misbehave and change their value from 0 to 1 or vice versa, or interchange their values amongst a group of bits, if their magnetic energy is changed. There are a lot of factors that can mess up with the magnetic energy inside it, which we will talk about soon.

This change in magnetic energy causes the data to misalign, and the sequence of bits of your photo is not the same anymore. This is called corruption. If that was an instruction for a program, it is now a different instruction that likely crashes the whole program or something similar.

This is an image:

This is how an image can look like after it is corrupted:

Wikimedia Commons

The change in the sequence of the bits causes a “bad sector” causing the original file to be rendered unreadable and useless.

All the causes of data corruption can be classified into:

  1. Human errors: Improper shutdowns of your PC, unexpected restarts while the hard drive is reading/writing data.
  2. Hardware failures: Such as background radiation, head crashes and aging or wear of the moving parts.
  3. Software failures: This can typically occur due to bugs in code or malware in the system or very rarely during data transmissions.

What Is Bit Rot?

Now don’t get us wrong, data storage is very reliable, but the data stored on these pieces of electronics can actually decay over time. For instance, if the electric charge can slowly leak to the environment due to imperfect insulation (usually in SSDs). Similarly, in HDDs, data can spontaneously change as the bits lose their magnetic orientation. We call this “bit rotting” (or “data rotting”, “disc rotting”, “format rotting”).

In these pictures, 1, 2, or 3 bits are randomly flipped (from a 0 to a 1 or vice versa). This shows that even the slightest bit rotting can seriously corrup the data.

Modern storage devices have built-in features to counter this; for instance, some hard drive software can keep a secondary copy of the files (usually in the cloud) to compare the bits to the original and see if the original is altered in any way. If you’re an average consumer, you probably won’t have to worry about this, unless you leave your drive unplugged over a very long period (such as 5-10 years).

So, it’s always good to keep a backup copy of your important data and although not necessary, an antivirus can protect your important files from corruption caused by malware.

Here are some signs your drives give you before going corrupt:

  • The Disk starts to hang or perform operations sluggishly
  • File error popup – “invalid file format”
  • Files and folders are displaced or lost
  • Computer regularly crashes and hangs without obvious reasons.