Hard Disk Drive vs. Solid State Drive

The absolute first decision to make as far as data storage is concerned is whether or not you want a solid state drive (SSD). While an SSD fulfills the same function as a traditional hard disk drive (HDD), it has its own set of pros and cons.

For those who don’t know, an SSD is a type of drive that uses something called flash memory for storing data instead the spinning metal disks you’d find in a traditional HDD. Think of it like a massive USB thumb drive.

What difference does it make, anyway?

First, SSDs are faster at reading and writing data. Second, SSDs require less power draw which conserves energy and extends laptop battery life. Third, SSDs have no moving parts so they make no noise and have longer lifespans.

The downside is that SSDs are more expensive and have smaller data capacities than HDDs.

What’s the bottom line? If price is a big concern, go with a traditional HDD. If you’re buying the drive mainly as a backup or external drive, go with a traditional HDD. If the drive is going to run an operating system or hold a lot of frequently-accessed files and programs, go with an SSD.

Physical Size and Interface

Once you’ve decided between an HDD and SSD, you have to pick a form factor. Thankfully, there are only two choices and the right choice will mostly be dictated by your current setup. Don’t worry, this decision will be easy.

Data drives come in two form factors: the 3.5-inch drive and the 2.5-inch drive

n traditional HDDs, data is stored on spinning metal disks, which means that more disks are needed for expanded data capacity. For this reason, desktop HDDstend to be 3.5-inches with a maximum capacity of 4TB while laptop HDDs tend to be 2.5-inches with a max capacity of 2TB.

On the other hand, SSDs can be made smaller because they don’t require movable parts. As such, most SSDs fit the 2.5-inch form factor. However, if you need to fit an SSD into a 3.5-inch connector, there are adapters available.

As far as connections are concerned, most modern consumer drives — both HDD and SSD — use SATA connectors. Older HDDs that were created before the SATA standard will likely use IDE connectors instead. And if you’re buying an external drive, it will connect to your system through a USB port.

Specifications and Performance

Now that you know what kind of drive to buy, it’s time to find the best one that fits your needs. Here’s what you need to consider.

Storage capacity: HDDs come in all sizes, capping out at 4TB per drive due to physical limitations. On the other hand, SSDs are much smaller and haven’t yet been able to break the 1TB mark. Even so, consumer-level SSDs rarely exceed 512GB.

Transfer speeds: The performance of a consumer-level HDD is determined by many factors, but revolutions per minute (RPMs) is an important one. Higher RPMs means faster transferring of data to and from the drive.

Also, ignore the drive’s SATA speed. For example, a modern drive might be listed as 3.0 GB/s and 7200 RPM. No HDD is ever going to be able to transfer data at speeds of 3.0 GB/s, but a 7200 RPM drive will always be faster than a 5400 RPM drive.

Cache space: When a hard disk needs to transfer data from one section of the drive to another, it utilizes a special area of embedded memory called the cache orbuffer.

Larger cache will enable the data to be transferred faster (because more information can be stored at one time). Modern HDDs can have cache sizes ranging from 8MB to 128MB.

Access times: Traditional HDDs have a couple of other factors that impact performance, such as the time it takes for the reader to position itself to read data from or write data to the drive.

While it’s true that two 7200 RPM drives could have differing performances — e.g. one of them might be slower at repositioning the reader — there’s no standard way to compare access times. Plus, most hard drives perform at similar levels these days, so I wouldn’t worry too much about this particular detail.

For SSDs, you’ll want to look for sequential read and write speeds (also called sustained read and write speeds). As long as those speeds are within the SATA connector’s max speed, which they most likely will be, you should be fine.

Failure rate: Since HDDs are mechanical, wear and tear is expected over time; that being said, not all HDDs are made equal. Some models are prone to fail within 6 months while others have average lifespans that exceed 6 years. It’s your responsibility to research this on a per-model basis prior to making a purchase.

On the whole, according to StorageReview, modern SDDs tend to last longer (average failure rate of 2.0 million hours) than modern HDDs (average failure rate of 1.5 million hours). However, for long-term disconnected storage, HDDs are far more reliable than SSDs.


Based on all of the above, you’re going to run into a wide range of prices for hard drives that look very similar on the surface. It’s up to you to decide which factors are most relevant to your needs and to select a hard drive that fits those parameters. To determine value for money, divide the drive’s retail price by its storage to get a price per gigabyte.

For example, the WD Black 1TB HDD ($70, $0.07/GB) is an all-around good purchase for the everyday consumer. However, bumping up the storage capacity to the WD Black 2TB HDD ($125, $0.06/GB) will nearly double the price. Bumping up the capacity again for the WD Black 4TB HDD ($222, $0.05/GB) will cost you a pretty penny. Although it’s hard to swallow, the 4TB drive offers the best value for money.

The trend is mirrored for solid state drives. The Crucial MX100 128GB SSD ($67, $0.52/GB) is affordable, but the Crucial MX100 256GB SSD ($105, $0.41/GB) is a little less than twice the cost for twice the space. When you get up to the Crucial MX100 512GB SSD ($200, $0.39/GB), your wallet will start to sweat, but it offers the best bang for your buck.

And as you can tell, the HDDs offer a whole lot more space than the SSDs even though they progress at similar price points.

External vs. Internal

The final thing to consider is whether this hard drive is going to housed within the casing, or used externally. It’s an easy decision, but let’s take a look at the pros and cons of each. External drives are perfect for storage and backups. They typically connect using a USB 2.0 cable which caps out at 480Mb/s, though later models may support USB 3.0 which caps out at 5.0Gb/s. Unless you can get one of the latter, the speed will likely be too slow for primary use (e.g. running an operating system).

The trade-off is that external drives are portable. They can be shared between multiple computers without any hassle. Just unplug the USB, plug it elsewhere, and you’re done. They can also be plugged into TVs and media centers for direct media playback.

If you need the speed, don’t need the portability, or if your system lacks a working data drive (e.g. if your last one malfunctioned and you need to replace it), then use it internally.

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