Many of us have a lot of general questions about the gear we rely on every day, including storage and backup technology.
We are here to demystify and explain in plain language how this stuff works. We’ll try to put it context for you as well, so you can understand not just how this stuff works but why it’s important to know. We hope you find it useful, and if you have any questions about this or other stuff you’d like to see us talk about, please sound off in the comments!
In this corner: the Hard Disk Drive
The traditional spinning hard drive has been a staple for many generations of personal computers. Constantly improving technology has enabled hard drive makers to pack more storage capacity on smaller drives than ever, at a cost per gigabyte that still makes hard drives the best bang for the buck.
 | As sophisticated as they’ve become, hard drives have been around since 1956. The ones back then were two feet across and could store only a few megabytes of information, but technology has improved to the point where you can cram 10 terabytes into something about the same size as a kitchen sponge. |
Inside a hard drive is something that looks more than a bit like an old record player: There’s a platter, or stacked platters, which spin around a central axis – a spindle – typically at about 5,400 to 7,200 revolutions per minute. Some hard drives built for performance work faster.
| Information is written to and read from the drive by changing the magnetic fields on those spinning platters, using an armature called a read-write head. Visually, it also looks a bit like the arm of a record player, but instead of being equipped with a needle that runs in a physical groove on the record, the read-write head hovers slightly above the physical surface of the disk. |  |
The two most common form factors for hard drives are 2.5-inch — common for laptops — and 3.5-inch, common for desktop machines. The size is standardized, which makes for easier repair and replacement when things go wrong.
The vast majority of drives in use today connect through a standard interface called Serial ATA (or SATA). Specialized storage systems sometimes use Serial Attached SCSI (SAS), Fibre Channel or other exotic interfaces designed for special purposes.
Proven technology that’s been in use for decades makes hard disk drives cheap — much cheaper, per gigabyte, than solid state drives – as low as three cents per gigabyte. You don’t spend a lot but you get lots of space. Hard drive makers continue to improve storage capacity while keeping costs low, so hard drives remain the champion of anyone looking for a lot of storage without spending a lot of money.
The downside is that hard drives can be power-hungry, generate noise, produce heat, don’t work nearly as fast as SSDs, and are ultimately mechanical devices, so they wear out over time.
In the opposite corner: the Solid State Drive
Solid State Drives (SSDs) have become much more common in recent years. They’re standard issue across Apple’s laptop line, for example — the MacBook, Retina MacBook Pro and MacBook Air all come with SSDs. So does the Mac Pro. Even Macs that don’t come with SSDs by default, like the Mac mini and iMac, have SSD options, or “Fusion Drives” which combine SSD and hard drive storage together.
| “Solid State” is industry shorthand for an integrated circuit, and that’s the key difference between an SSD and a hard drive: there are no moving parts inside an SSD. Rather than using disks, motors and read/write heads, SSDs use flash memory instead — that is, computer chips which retain their information even when the power is turned off. |  |
| SSDs work in principle the same way the storage on your smartphone or tablet works. But the SSDs you find in today’s Macs and PCs work faster than the storage in your mobile device. | |
The mechanical nature of hard disk drives limits their overall performance. Hard drive makers work tirelessly to improve data transfer speeds and reduce latency and idle time, but there’s a finite amount they can do. SSDs provide a huge performance advantage over hard drives – they’re faster to start up, faster to shut down, and faster to transfer data.
What’s more, SSDs can be made smaller, can use less power than hard drives do, don’t make noise, and can be more reliable because they’re not mechanical. As a result, computers designed to use SSDs can be smaller, thinner, lighter and last much longer on a single battery charge than computers that use hard drives.
 | Many SSD makers also produce SSD mechanisms that are designed to be plug-and-play drop-in replacements for 2.5-inch and 3.5-inch hard disk drives, because there are millions of existing computers (and many new computers still made with hard drives) that can benefit from the change. They’re equipped with the same SATA interface and power connector you might find on a hard drive. |
SATA itself can be a bottleneck for SSD, so computer makers designing custom SSD storage for their systems are often opting for different interfaces that provide better throughput and more thorough data optimization for SSDs. Apple uses PCI Express (PCIe) on its newer devices, for example. PC makers often opt for M.2 on their SSD systems. Check your computer’s specifications for more details on what it uses.
Just like hard drives, SSDs can wear out, though for different reasons. With hard drives, it’s often just the mechanical reality of a spinning motor that wears down over time. Although there are no moving parts inside an SSD, each memory bank has a finite life expectancy — a limit on the number of times it can be written to and read from before it stops working. Logic built into the drives tries to dynamically manage these operations to minimize problems and extend its life.
If you’re still using a computer with a SATA hard drive, you can see a huge performance increase by switching to an SSD. What’s more, the cost of SSDs has dropped dramatically over the course of the past couple of years, so it’s less expensive than ever to do this sort of upgrade.
For practical purposes, most of us don’t need to worry about SSD longevity. An SSD you put in your computer today will likely outlast the computer. But it’s sobering to remember that even though SSDs are inherently more rugged than hard drives, they’re still prone to the same laws of entropy as everything else in the universe.
This brings up an important point: Whether you’re using a hard drive or an SSD, a good backup plan is essential. Because eventually your drive will fail. You should have a local backup to recover from quickly, combined with secure cloud-based backup like Backblaze. To help get started, make sure to check out our Backup Guide.
Fusion Drives and Hybrid SSDs
Earlier we mentioned Apple’s “Fusion Drive.” This offering from Apple is available on the iMac and Mac mini (it’s standard issue on some configurations, optional on others). It combines a discrete SSD with a discrete hard drive mechanism, combined together to form one logical volume the computer sees as a regular storage device. Software running on OS X behind the scenes adjusts where the data is being stored (either on the SSD or the hard drive). You as the user simply see that a Fusion Drive works faster than a plain old hard drive by itself. It’s the best of both worlds: Better performance, while still retaining a reasonable cost per gigabyte.
Apple isn’t the only computer maker that’s putting both SSDs and hard drives into their systems, either. While “Fusion Drive” is an Apple appellation, the concept of combining SSD and hard disk storage can be replicated on Windows too.
Similarly, SSDs have caught the eye of hard disk drive makers who are anxious to see these performance improvements carry over to their devices as well. So there are a few “hybrid” drives available now which combine a small amount of on-board SSD with a regular hard drive. These can be cost-effective ways to improve performance and storage capacity on your computer without breaking the bank, though they don’t yield the same performance benefit as a pure SSD.
Hopefully we’ve given you some insight about hard drives and SSDs. And as always, we encourage your questions and comments, so fire away!
Next in our What’s the Diff series, we’ll be talking about the differences between memory (RAM) and storage, and how they work together to effect performance on your computer.
