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What’s the difference between a hard drive and a solid state drive?

SSDs are the future, but HDDs aren’t useless.

An M.2 SSD grasped between a person's fingers Credit: Getty Images / Михаил Руденко

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Hard drives have been around since the 70s as the first way to store data after you shut off the computer. We’ve come a long way since the fridge-sized disks of then, with thumb-sized solid state drives offering Terabytes of storage. Solid state drives are an improvement over hard drives in many ways.

They’re denser, faster, and more durable than hard drives. Because solid state drives are completely digital, they also draw less power than hard drives and make no noise. Hard drives are still around because they’re so cheap, but as electronic components get smaller and new technologies arise, solid state drives become cheaper and cheaper.

What is a storage drive?

HDD over notebook keyboard, selective focus
Credit: Getty Images / Gilmanshin

Although HDDs are a legacy technology, they are excellent for backup storage.

A hard disk drive (HDD), or hard drive, is a nonvolatile storage drive that works by reading and writing information to physical disks called “platters.” The hard drive spins the platters to record the data using magnetically charged spinning needles like a vinyl player. Usually, hard drives sit in a 2.5-inch or 3.5-inch storage bay in the computer. To send the data through the motherboard, most modern hard drives connect with a Serial ATA (SATA) cable.

The solid disk drive (SSD) is also a nonvolatile storage device, but unlike an HDD, an SSD has no moving mechanical parts. The information is read and stored electronically into NAND circuits or flash memory.

While an SSD can live in its own bay and use a SATA connector like HDDs, most SSDs connect directly to motherboards with the much faster NVMe ports. Usually, SSDs come as 2.5-inch wide drives connected with SATA, or they live directly on the motherboard in an NVMe port.

The NVMe drive itself can come in a variety of sizes, but most desktop computers use M.2 2280 SSDs (M.2 is the form factor while 2280 refers to the length of the SSD board). Many laptops also use M.2 2280 SSDs, but sometimes they will use smaller, denser drives to make laptops thinner—the smallest SSDs are in handheld devices like phones.

Storage size

Different types of SSD disk drive isolated on laptop keyboard. Classic SSD and SSD m2. 3d illustration.
Credit: Getty Images / Bet_Noire

Older SATA SSDs are slower and bigger than the newer M.2 NVMe SSDs that go directly on the motherboard.

Space-wise, an SSD can be extremely small—the limiting factor is the size of its integrated circuits (ICs), which are constantly getting smaller as the years go on. Hard drives can’t be smaller than 2.5 inches wide because of the way they work. This is why you don’t see hard drives in thin devices like tablets or smartphones.

However, SSDs are usually smaller in storage capacity, as well; a 1TB SSD goes for about $100 at the time of writing, and prices quickly balloon as you go past that 1TB mark in a single drive. There is no technical cap on the storage capacity of an SSD; the more ICs that can fit on the board, the more storage it has. The largest drive is a massive 100TB, but the largest consumer drives are 8TB.

Hard drives are much cheaper than SSDs for the same storage capacity with 1TB selling for about $35. The largest hard drives are about 20TB. Because it’s an older and more developed technology, there isn’t much room left for innovation to make hard drives denser or cheaper.

Performance and speed

A hard drive can run at up to 7,200 rotations per minute (RPM), but it needs to rev up to reach those speeds. At its peak, it can read and write around 80 to 160 Megabytes per second (MB/s). Older SATA SSDs can read and write data up to 550MB/s, but the newer and more common NVMe SSDs have a peak speed of up to 8000 MB/s—but you’ll usually see speeds closer to 1000 MB/s.

Even the slowest NVMe SSDs are ten times faster than HDDs. This is why you want to have one for your main storage drive. While SSDs can boot a PC in seconds, boots from HDDs can take two minutes or more. Because loading programs takes so much more time on HDDs, you want to keep your most frequently used programs and your operating system running from an SSD as your main (C:/) drive.

However, for files that are infrequently accessed or for small files, an HDD can be a great secondary storage drive in your system. Things like word documents, music, and videos will load fairly quickly from a hard drive since they’re small files.

Durability and longevity

A hard drive on a white background.
Credit: Crucial

HDDs are mechanical, which means they do not need electricity to store data.

For most use cases, SSDs are more reliable than HDDs, but HDDs have some niche benefits. Because data on HDDs is physically stored instead of electronically stored, it’s less likely to degrade or corrupt over time if unused for long periods of time. Because SSDs need an electric charge to work, they usually have small batteries to keep them powered at all times, but if you leave an SSD lying around for a year or more, it could start to lose data once its battery runs out. A hard drive is the better option if you’re planning to archive data for a decade or more.

However, hard drives are also more fragile than SSDs. Their mechanical operation means they’re prone to breakage if you drop them, expose them to extreme temperatures, or expose them to a strong magnetic field. The average person might not be tossing their storage drives into space, but considering how likely you are to drop your laptop or desktop at least once in its life, the SSD’s drop resistance is a godsend.

Another improvement SSDs made over HDDs is in how it writes over old data. Because everything wears out over time, SSDs and HDDs both have a limited lifespan when it comes to how many times you can write and rewrite on the same cell or section. Additionally, revisions to digital files can end up on a different part of the drive than the original file, which is what leads to fragmentation.

Fragmentation can seriously affect an HDD’s performance, so they need to be defragmented occasionally to keep them as fast as possible. SSDs use a few processes to prevent fragmentation and prolong the life of the drive overall, like wear leveling.

You can expect a hard drive to last about five years before it starts to fail. Reading and writing data affect its longevity, so it wears out fairly quickly if you use it daily. Meanwhile, SSD longevity is most dependent on writing data. They’re rated for a maximum number of rewrite cycles (usually 7,000 to 10,000 rewrites) before they run into issues, but the average person won’t reach it for decades.

Price

HDDs are almost always much cheaper than SSDs with the same storage capacity—$35 per Terabyte versus $100 per Terabyte. However, prices can vary a lot for SSDs in particular. The newest, fastest SSDs can go for as much as $150 for a 1TB drive. If you’re looking for an external storage drive, the ruggedness and durability of the case can add to the cost, as well.

Best use case for each technology

olid state drive SSD, Hard Disk Drive HDD and M2 SSD ratings concept. 3D rendering isolated on white background.
Credit: Getty Images / AlexMLX

The size of an SSD depends on the number and size of its transistors.

Strictly speaking, the much newer SSD technology is faster and more reliable than HDD technology, but that does not mean HDDs shouldn’t have a place in your life. The much older tech is also much cheaper, so you can buy an HDD with a lot more storage capacity than an SSD of the same price.

If you have multiple terabytes of data that you want to keep around (photos, videos, business or school files) even though you don’t access them often, a hard drive will save you a lot of money. For frequently used files or data that need to be accessed quickly, an SSD’s upsides will more than make up for the initial cost difference.

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Prices were accurate at the time this article was published but may change over time.