Hard Disk Drive Versus Solid State Drive: What’s the Diff?

March 8th, 2016

This is first in a new series of blog posts we’re calling What’s the Diff? Many of us have a lot of general questions about the gear we rely on every day, including storage and backup technology.

What’s the Diff is 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.

IBM Ramac 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. Hard Drive exploded view

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. Inside an SSD
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.

SSD Conversion Kit 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.

Peter Cohen
Peter will never give you up, never let you down, never run around or desert you. He also manages the Backblaze blog.

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His web site: peter-cohen.com | Twitter: @flargh | LinkedIn: Peter Cohen | Google+: Peter Cohen
  • Niks Chopra

    Hello everyone i want to Know that What is the Max Flash Storage Available in the Market to use that into PC or laptop?
    And what is the Price for That if i would Like To Buy that From The wholesale,not the Market(retail) Price From the Dealer?
    Reply Me Here ASAP.
    Thank You.

  • Jesus Nervous

    Ssd is overrated ripoff

  • Dustin DeTorres

    Great Post Peter. HDD vs SSD. Very popular question in data recovery industry. SSD always win this race. This blog post Battle of the Drives gave some important facts. You may like it.


    The Winner between the SSD and HDD is SSD.

  • aaron

    please never use a shortened and inaccurate version of the word difference in a professional review of computer parts again. this article’s title is the source of my indirect autism. please. dear god.

  • Ashok Rajaram

    I am planning to buy a laptop having both SSD(128 GB) and 1TB hard disk drive built in. Will there be any dip in performance? To get a better performance,do you suggest having both or any one of those?

    • SSDs are faster than conventional hard drives, so for max performance go with SSD. Combining both is a popular option these days, and that elicits a lot better data transfer performance than a conventional hard drive alone.

  • SSD Tester

    SSDs are just way better than the old HDDS. you can find reviews on different SSDs on this Website: http://ssd-tests.eu/
    Thanks a lot
    SSD tester

  • Go Kevin

    Thanks for the explanation of the differences between the 3 types.

    Cloud based storage is not for me, not saying you would but stories about the cloud based storage, the data is looked at and in the case of micro?+%& using said data to force tailored adverts to your system, just as some phone companies that offer cloud storage can. Also the data can be hijacked, hacked and ID theft is more common now.

    yes I have photos, music and movies. 99% is backed up to external drives.
    As for ssd yes considering getting a small one 120 gb to use as a c: drive. But this will not really benefit me as I am not into heavy gaming and video editing, which would be a good use for them.
    Boot up from sata to using system is less than a minute, I’m now dressed and ready. An ssd 5-8 seconds.
    A better use for me would have it as a pen/thumb drive as they are faster than usb 3 pen/thumb drives. Not used the new ones yet usb c, supposed to be faster.

  • Scott McCarty

    Who needs proofreaders when the Internet is loaded with grammar/spelling Nazis. :-D

    • rna

      why do you waste our time
      with your “look at me” attitude !!!

  • Jon Forrest

    “and extend it’s life.” -> “and extend its life.”

  • James Brown

    Not sure that’s the correct use of the word ‘appellation’, and it’s missing an ‘l’. :-)

    I liked the article, but am interested in your thoughts on the new generation of SSDs about to appear, which are even faster and have capacities up to 16TB.

    Could these be the end of hard drives? Has Backblaze had a chance to evaluate any?

  • joer80

    How do SSDs stand up in years of use compared to spinning disks?

    • We (Backblaze) don’t have enough SSDs to produce numbers as statistically significant as our hard drive reports. With that said, our oldest SSDs in our datacenter are about 5 years old (running in Zabbix monitoring servers running in MySQL databases that are hammered constantly) and we have never had an SSD fail in the datacenter. So the preliminary information is leaning towards SSDs being at least as reliable as hard drives. As always, in any one case you might have an SSD that fails so no matter how they stand up to abuse you need backups!

    • Defenestrator

      The best data to date is the Google report: http://0b4af6cdc2f0c5998459-c0245c5c937c5dedcca3f1764ecc9b2f.r43.cf2.rackcdn.com/23105-fast16-papers-schroeder.pdf

      The torture test done by TechReport is also interesting, though the sample size is tiny: http://techreport.com/review/27909/the-ssd-endurance-experiment-theyre-all-dead

      TL;DR: quite well. Wear limits set by the manufacturers are pretty conservative, and failures tend to be linear rather than exponential once they’re passed. Just a few little caveats, though:
      1. SSDs will lose data if left sitting unpowered for long enough (months to years)
      2. Recoverable errors don’t predict unrecoverable errors, so they’re not necessarily any more likely to warn you about their impending death than a spinning drive.

    • It really depends on SSD vendor. There are so many SSD manufacturers and quality of SSD model families varies so much… According to my experience, it is difficult to say anything for sure unless you stick to some famous models like Samsung 850 Evo/Pro…

  • Have you implemented SSDs in any of your storage units yet? I’d actually think not given your requirement is space over speed (after all, spinning rust will still outpace an internet connection.) But if you have I’d love to see how they stand up from a reliability point of view in your regular reliability reporting of drives.