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What is the difference between an HDD (hard disk drive) and an SSD (solid-state drive)?

Hard drives and SSDs are both used for PC storage, but the former is composed of discs, called platters, and a metal arm, called an actuator arm that reads and writes data as it moves over the surface of the spinning platters. As their name suggests, solid-state drives have no moving parts. Hard drives are much more commonplace, relatively inexpensive, and come in massive capacities, up to 4TB (terabytes). SSDs are a newer technology, generally cost more than hard drives, but are capable of achieving significantly faster read and write speeds.

Hard drives are most commonly 3.5-inch devices, though 2.5-inch hard drives are also common and used for notebooks and compact PCs. SSDs are almost exclusively sold in the 2.5-inch form factor.

Hard drives also come in 1.8-inch form factors, but these are fairly uncommon.

How does a hard drive interface with a PC?

Hard drives for sale today most likely feature the SATA (Serial Advanced Technology Attachment) interface, which uses a narrow L-shaped plug for data communication and a wider L-shaped connector for power. Older hard drives, called EIDE (Enhanced Integrated Drive Electronics), use a 39-pin interface for data communications and a 4-pin power connector. The data cables for EIDE hard drives are typically wide and flat, which is why they’re typically referred to as ribbon cables.

What is the difference between SATA 2 and SATA 3?

Like most standards, SATA is constantly evolving. Of the hard drives you can buy today, SATA 2 and SATA 3 are your main options. SATA 2-based hard drives have a peak throughput of 3.0Gbps (gigabits per second). SATA 3-based hard drives can achieve up to 6Gbps throughputs. Keep in mind that to support these speeds, the hard drive must be plugged into a SATA port on the motherboard that is capable of supporting the same speed. For SATA 3 hard drives, it’s also important to use cables that are designated for 6Gbps throughput.

What are RPMs, and why should I care?

Hard drives read and write data as the platters inside spin. The faster the platters spin, the more quickly the required disc sector will arrive at the actuator arm and the read/write head. High RPM (revolutions per minute) hard drives offer lower latency and faster overall performance.

The most common speed for hard drives is currently 7,200rpm. Hard drives that spin at 5,400rpm are also very common.

Hard drives that target the enterprise market or enthusiasts can spin at 10,000rpm and 15,000rpm, but such hard drives are significantly more expensive than the slower-spinning alternatives.

When should I use an HDD or SSD?

As previously mentioned, hard drives have an advantage over SSDs when it comes to capacity and price, but SSDs are quickly catching up in those areas. If you find yourself considering using both an HDD and SSD in your computer, don’t make the mistake of using them interchangeably. Due to HDD’s slower performance and higher capacity, it makes the most sense to use them as photo, music, and video storage, largely because those files don’t require massive throughput to display or play back. Storing the operating system and a few frequently used applications on an SSD can significantly speed your overall computing experience.