SSD vs. HDD: which is better?
For running a computer, an SSD, by a lot. A solid-state drive stores data on flash chips with no moving parts, so it reaches any file almost instantly. A hard disk drive has to swing an arm across a spinning plate and wait for the right spot to come around. Hard drives are still cheaper per gigabyte, which makes them fine for backups.
How a hard drive works
Inside a hard drive, metal or glass platters spin thousands of times a minute. A head on a moving arm floats just above them, reading and writing tiny magnetic patches. To get any file, the arm has to move to the right ring, then wait for the right spot to spin under it.
That moving and waiting is fine for one big file, like a movie. It’s terrible for the thousands of small files a computer reads when it starts up or opens an app.
How an SSD works
An SSD stores each bit by trapping electrons in tiny cells on flash memory chips, the same kind of memory in a USB stick or your phone. Nothing moves, so there’s nothing to wait for, and it can read from many chips at once. For small scattered files, it can be dozens to hundreds of times faster than a hard drive.
Most slow computers aren’t short on processor speed. They’re waiting on something slower: memory that’s full, a hard drive with a spinning plate, or the internet. The processor is so fast that every trip to anything else is a long wait by comparison. Here’s how long, if one processor tick took one second.
This is the same toy that’s in the app.
If one processor tick took one second, and everything else stretched to match.
Why it’s the best upgrade for an old computer
On an older computer with a hard drive, the drive is usually the bottleneck: the processor sits mostly idle, waiting for files to arrive. Swapping in an SSD often turns a four-minute startup into fifteen seconds. Back up first, buy the right shape for your model (an older laptop usually takes a 2.5-inch SATA drive, newer ones a small M.2 stick), and either clone the old drive or install the system fresh.
Where hard drives still make sense
Backups
An external hard drive is one of the cheapest ways to back up a whole computer.
Big libraries
Video collections and archives you don’t open every day.
The cloud
Data centers store enormous amounts on hard drives, because they’re cheapest at that scale.
Questions people ask
Do SSDs wear out?
Slowly. Each flash cell handles a limited number of rewrites, but the drive spreads writes evenly across all of them. For everyday use, the rated life is many years, usually longer than the rest of the computer lasts.
What’s the difference between SATA and NVMe?
They’re two ways an SSD connects. SATA is the older connection hard drives used. NVMe plugs more directly into the motherboard and can be several times faster. Either is a huge step up from a hard drive.
Learn it by taking one apart
The app teaches hard drives in Module 10, Spinning Platters, and SSDs in Module 11, No Moving Parts, where an SSD swap brings Grandma Ruth’s laptop back to life.
How Computers Work is a course in five-minute lessons, with something to play with in every one and an old laptop the crew fixes along the way. Part I is free. Coming soon to iPhone, iPad and Android; the toys on the course page work right now.
Keep going
What is RAM, and how much do you need?
Your computer’s working space, why it forgets, and how much you need.
CPU vs. GPU: what’s the difference?
A few brilliant cores vs. thousands of simple ones, and why AI wanted the second.
Mac vs. Windows vs. Linux: which should you get?
Three families plus ChromeOS, where they came from, and how to choose.