Data Security

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A frequent concern with donating a computer is the sensitive information that could be stored on it. If you choose to donate your used computer, how can you be sure that you're not donating your entire life with it? Here's a brief summary of how data storage works, and more importantly, how data removal works!

Reminder: I will always destroy all data on any drive I receive! There are many reasons for this, but respect tops the list. Whether it's vacation photos or military secrets, no one gets to see it without your permission, not even me. This page is just my attempt to help you understand how it all works and what you might try yourself should you feel so inclined.

Note: I am not a data security expert, but instead simply wish to present what I have learned through my experience and what is true to the best of my knowledge. I advise you corroborate any of this on your own, and to seek true professional advice for your most sensitive concerns.

Types of Storage

All computers store data internally on what is commonly called a "hard drive" (or more accurately, a "storage drive"). Data is stored in an amazing array of 1's and 0's, ons or offs, highs or lows, however you want to think about it. The point is that it is physically stored somewhere inside your computer in a specific device. There are two dominant forms that dictate not only how data is stored, but how it should be removed.

Hard Disk Drive (HDD)

This has been the standard for many years, and should be familiar to most of us. Hard disk drives (abbreviated HDD) contain actual spinning disks (technically referred to as platters) reminiscent of a vinyl record or CD, and the data is read and written using tiny, amazingly precise arms that magnetically polarize individual points on the platters, resulting in a pattern of the familiar binary 0's and 1's. They're relatively inexpensive, extremely common, and can last a very long time if not physically damaged (don't drop your laptop!). 

You'll find these everywhere, from desktops to laptops to external USB drives. That's right, your external backup drive is often just the same HDD you might find in a laptop or desktop, just inside a spiffy little case!

Solid State Drive (SDD)

This type of storage device is becoming increasingly more common due to several advantages. They're smaller, lighter, come in many forms, are power efficient, and are much faster! Solid state drives contain no moving parts. If you open one up (if it even has a case), you'll see only computer chips. That's where all the data is! It's stored in the same binary manner, just instead of creating magnetic fields on a disk or platter, it's stored as an electric charge (or lack thereof) inside those little black chips. Nothing has to physically move to get to the data, the drive just needs to be told which data to retrieve.

Due to the size and speed advantages of SDD's over HDD's, you'll find these in more recent and higher end computers, but especially in small and thin laptops. MacBooks made the switch in the early 20-teens. Small PC laptops where portability is key (like my beloved Dell Latitude E7250 from 2015) may choose an SSD for their thin size and lower power consumption. Higher end PC's often choose SSD's for their big speed advantage.

One key difference of an SSD is that every time a bit is written, that spot on the chip physically degrades ever so slightly. There is a finite number of times data can be written to an SSD, and they use special tricks to deal with this fact of nature when saving your data. This also affects how to properly get rid of data on an SSD.

Ok, so what? Why do I care what kind of drive I have?

Erasing Your Data

When you hit the Delete key or send a file to the recycle bin/trash, even if you empty it, the file is not really gone. Simple, free programs exist to "undelete" files and this is possible not through magic or time travel, but simply because those files are still right where you left them on your drive. When you delete a file, you don't actually delete the file, you just sort of tell the hard drive to forget about it and mark the space where it exists on the drive as eligible for new data to be written. Until new data gets written over the old file, it can be 100% recovered. So how do you get rid of it for good?

Cleaning an HDD

Lots of programs exist to perform a deep, thorough clean of a hard disk using the principle that if you overwrite a file, it can't be recovered. A common method is to write 0's to every bit on the drive, go back and write 1's on every bit, and go back yet again and just write random data. As you can imagine, this takes quite a while, but at the end of it you can rest assured that your data is pretty much unretrievable.

• On Windows 10/11: Windows will actually do this for you! Go to Settings > Update & Security > Recovery, and there you'll find the ability to "Reset this PC" which includes the option to clean the disk. Just start it up and check back in the morning because it does take a few hours depending on the size of your drive.

Windows 10 Support: How to refresh, reset, or restore your PC 

Another option may be inside your PC's firmware (called BIOS or UEFI, the first thing that runs when the computer turns on). Depending on the manufacturer, there may be an option to clean your hard drive in there. 

Dell BIOS Info 

HP BIOS Info 

• On Mac OS: Apple's Disk Utility does provide the option to "securely erase" your disk, though it isn't as convenient as the Windows tool in that it can't erase the disk you're running Mac OS from. So to fully reset your Mac you'll need to either boot into recovery mode and use Disk Utility from there, or create bootable installation media which will contain Disk Utility, boot from that, and use that to erase your internal drive. 

Apple Support: Erase and reformat a storage device in Disk Utility on Mac

Disk Utility contains options for securely erasing under a button labeled "Security Options" that you'll find somewhere in the process depending on what version of Mac OS you're using.

Cleaning an SSD

This is trickier because SSD's don't necessarily work like HDD's, and telling a program to write 0's and 1's everywhere might not actually work as expected. Additionally, it's just not great for the drive to do that. Now practically speaking, 3 writes probably isn't going to kill the drive, but if you don't have to do it, it's best not to. Multiple passes is also not necessary.

Perhaps the easiest way to clean an SSD using tools built into your computer is to encrypt the drive, then do a normal erase. This is analogous to locking all your data in a safe (encryption), throwing it in the ocean (erasing the drive), and throwing away the key (deleting the encryption key). Even if someone finds your deleted data, it's unreadable and useless without the key which is erased and/or overwritten.

MakeUseOf: How to Securely Erase Your SSD Without Destroying It 

Backblaze: Guide to How to Wipe a Mac or Macbook Clean  

Mac Observer: How to Securely Erase Your Mac 

Removing your Storage Drive

If you really want to be sure your data never leaves your custody, the surest way is to physically remove the component where it's stored. Remember, as abstract as data storage may seem, it is still physically stored on something you can hold in your hand and, most often, something you can remove. This is usually pretty easy with a small enough screwdriver, but it depends on the model. You'll have to do a search for the location and removal procedure for your specific make and model. For some of the most obnoxious Mac's (and even some PC's these days), the drive may be built into the motherboard and not removable. Don't get me started on that...