What is the difference between SSD and HDD?

When you’re shopping for computers, you may find some computers have an SSD and some list an HDD in the specs instead. What is the difference between SSD and HDD? And should you care? In a word, yes.

How they work

Both HDDs and SSDs are storage devices, a permanent holding area for programs and data. When you save files “to the hard drive,” in popular terminology, that’s the drive you’re using.

HDDs use metal platters with magnetic particles on them to record data. We don’t use magnetic media with computers nearly as often as we used to, especially in the consumer space. There, the HDD is the last holdout of a technology that’s been around for decades. A motor in the drive spins the platters at high speed, while an arm containing read/write heads hovers just barely over the platters to either record or play back data. This technology has existed since the 1950s, though it’s improved considerably in terms of speed, reliability, and capacity over the years.

SSDs store their data on memory chips. The circuit board inside an SSD just looks like an overgrown memory module, because that’s essentially what it is. It’s a different type of chip from your computer’s main memory, which allows it to retain data with the power off. It’s not as fast as your computer’s main memory either, but it’s a lot faster than a traditional HDD.

Advantages of HDDs

The main advantages of HDDs are capacity and cost. You can get a 10 TB HDD if you want it. SSDs with that kind of capacity don’t exist. And you can get a 1 TB HDD for $35, compared to around $135 for a 1 TB SSD. The cost advantage is narrowing, and it’s going to narrow even more over the course of 2019, but for now at least, HDDs cost less than SSDs. But the days of an SSD costing 10 times as much as an HDD are over.

I predicted in 2015 that the two drive types would reach price parity sometime in 2021. It may happen sooner than that. If it does, I won’t be disappointed that I was wrong.

Advantages of SSDs

The biggest advantage of SSDs is speed. SSDs trounce HDDs both in terms of maximum speed and in latency. A Ferrari goes from 0 to 60 much faster than a lawn tractor. That’s latency. A Ferrari’s top speed is also much faster than a lawn tractor.

In real-world performance, SSDs don’t get to cruise along at maximum speed for long periods of time. But generally, even when they’re doing the things they’re worst at, they’re still faster than an HDD’s typical speeds. I’ve been putting SSDs in computers since 2009, and I don’t like using one with an HDD. It feels laggy.

SSDs have a reliability advantage too. They have a typical life expectancy of 10 years and they fail predictably. HDDs can generally warn you when they’re about to fail, but sometimes they don’t figure out they’re failing in time for you do to anything about it. An SSD can look at its usage history and predict how much life it has left based on those usage patterns. This lets you plan years in advance. But realistically speaking, I’ve never had to replace an SSD due to imminent failure. By the time the drive is nearing the end of its life expectancy, it’s too small for me to be using it for much anymore.

If you buy a 240 GB SSD today, it will probably still work in 2028, but how useful the drive will be then is a good question.

Types of SSDs to avoid

In case you haven’t figured it out, I really like SSDs and I recommend them enthusiastically. But not all SSDs are created equal. There are certain SSDs I would avoid buying, and I recommend you avoid them too.

eMMC SSDs

Some inexpensive computers come with eMMC SSDs. These have cheaper chips in them than regular SSDs do, so they aren’t nearly as fast. They’re also usually soldered directly onto the motherboard, so you can’t unplug them and upgrade them. I like SSDs that are a discrete component, that plug into a SATA or M.2 port. This allows me to upgrade them whenever I want. And in the unlikely event of the drive failing, I can swap out the part. I can’t do that with an SSD soldered to the motherboard. When one of those fails, I may have to discard the whole computer.

Don’t buy a $149 laptop from a consumer electronics store. Buy an off-lease business laptop instead. You should even be able to find an off-lease business laptop with a pre-installed SSD, even if it means paying $199 instead of $149. The result is a much better computer.

Small capacity SSDs

It’s also best to avoid the smallest capacity SSDs on the market. Generally speaking, today that’s 120 GB. They work fine, but they aren’t as fast as higher capacity drives because they can’t spread their workload across very many chips. So a 240 or 480 GB drive in the same family will work much faster, and you’ll be much happier with it.

Granted, 120 GB drives are very inexpensive now, and if they’re all you can afford, they’ll still outrun any hard drive. But if you can pay a 50% premium to get a 240 GB drive, you’ll be happier.

The cheapest SSD you can find

You also want to avoid going onto Chinese importer sites and just buying the cheapest SSD you can find there. When you cut every corner possible to make the cheapest drive you can, you end up with a poor-performing drive, and some of those compromises they made to cut the price may also affect longevity too. I’ve always had the best luck with big-name SSDs because those companies make the chips and get the best chips for their drives. I recommend Samsung, Crucial/Micron, and Intel drives whenever possible. But there are some lesser brands who are making good drives. I always try to get a review first. Silicon Power drives generally aren’t very good.

If you’re buying a computer with an SSD pre-installed, it probably comes from a fairly reputable maker.

What is the difference between SSD and HDD: In conclusion

HDDs still have their adherents, and for mass data storage, they’re still the better choice. But for general use inside a computer, SSDs are very compelling, and will continue to be.