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Last Updated on July 14, 2021 by Gabriel Goddy

HDD and SSD are key components of a computer. They also have similar functions, however, they are different. In this guide, we would consider the differences between HDD and SSD.


The technology behind hard disk drives is well known and well-tested. Hard disk drives have been around for more than 50 years, steadily increasing their storage capacity and decreasing their physical size. HDDs rely on spinning disks, or platters, to read and write data.

HDDs are considered a legacy technology, meaning they’ve been around longer than SSDs. In general, they are lower in cost and are practical for storing years of photos and videos or business files. They are available in two common form factors: 2.5 inches (commonly used in laptops) and 3.5 inches (desktop computers).

How hard drives work

Hard disk drives consist of one or more magnetically sensitive platters, an actuator arm with a read/write head on it for each platter, and a motor to spin the platters and move the arms. There is also an I/O controller and firmware that tells the hardware what to do and communicates with the rest of the system.

Each platter is organized into concentric circles called tracks. Tracks are divided into logical units called sectors. Each track and sector number results in a unique address that can be used to organize and locate data. Data is written to the nearest available area. There is an algorithm that processes the data before it’s written, allowing the firmware to detect and correct errors.

The platters spin at preset speeds (4200 rpm to 7200 rpm for consumer computers). Those speeds correlate to read/write rates. The higher the preset speed, the faster a hard drive will be able to read and write data.

SSD (Solid State Drive)

Solid-state drives use flash memory to deliver superior performance and durability. Because there are lots of small, moving parts inside your hard drive — magnetic heads, spindles, and spinning platters — it’s easy for things to go wrong and you could lose your important data. Without moving parts, SSDs are more durable, run cooler, and use less energy.

SSDs are more expensive than HDDs per amount of storage (in gigabytes, or GB, and terabytes, or TB), but the gap is closing as SSD prices begin to drop.

How NAND works

SSDs can be thought of as large USB drives; they use the same base technology. NAND, the technology in solid-state drives, is a kind of flash memory. At the lowest level, floating gate transistors record a charge (or lack of a charge) to store data. The gates are organized in a grid pattern, which is further organized into a block. Block size can vary, but each row that makes up the grid is called a page.

An SSD controller performs several functions, including keeping track of where data is located.

A History of HDDs and SSDs

Hard drive technology is relatively ancient (in terms of computer history, anyway). There are well-known photos of the IBM 650 RAMAC hard drive from 1956 that used 50 24-inch-wide platters to hold a whopping 3.75MB of storage space. This, of course, is the size of an average 128Kbps MP3 file today, stored in the physical space that could hold two commercial refrigerators. The RAMAC 350 was limited to government and industrial uses, and it was obsolete by 1969. How far we’ve come!

The PC hard drive form factor standardized at 5.25 inches in the early 1980s, with the now-familiar 3.5-inch desktop class and 2.5-inch notebook-class drives coming soon thereafter. The internal cable interface has changed over the years from serial to IDE (now frequently called Parallel ATA, or PATA) to SCSI to Serial ATA (SATA). But each essentially does the same thing: connect the hard drive to the PC’s motherboard so your data can be shuttled to and fro.

Today’s 2.5- and 3.5-inch drives mainly use SATA interfaces (at least on most PCs and Macs), though many high-speed internal SSDs now use the faster PCI Express interface instead. Capacities have grown from multiple megabytes to multiple terabytes, more than a million-fold increase. Current 3.5-inch hard drives are now available in capacities exceeding 10TB.

The SSD has a much shorter history, though its roots do reach several decades into the past. Technologies like bubble memory flashed (pun intended) and died out in the 1970s and 1980s. Current flash memory is the logical extension of the same idea, as it doesn’t require constant power to retain the data you store on it.

The first primary drives that we know as SSDs started appearing during the rise of netbooks in the late 2000s. In 2007, the OLPC XO-1 used a 1GB SSD, and the Asus Eee PC 700 series used a 2GB SSD as primary storage. The SSD chips on these laptops were permanently soldered to the motherboard.

Advantages and Disadvantages of SSDs and HDDs

Hard drives are still around in budget and older systems, but SSDs are now the rule in mainstream systems and high-end laptops like the Apple MacBook Pro, which does not offer a hard drive even as a configurable option. Desktops and cheaper laptops, on the other hand, will continue to offer HDDs, at least for the next few years.

That said, both SSDs and hard drives do the same job: They boot your system and store your applications and personal files. But each type of storage has its own unique traits. How do they differ, and why would you want to get one over the other?

  • SSD vs. HDD Pricing

SSDs are more expensive than hard drives in terms of dollar per gigabyte. A 1TB internal 2.5-inch hard drive costs between $40 and $60, but as of this writing, the very cheapest SSDs of the same capacity and form factor start at around $100. That translates into 4 to 6 cents per gigabyte for the hard drive versus 10 cents per gigabyte for the SSD. The differences are more drastic if you look at high-capacity 3.5-inch hard drives. For example, a 12TB 3.5-inch hard drive that sells for around $300 to $350 can push the per-gigabyte cost below 3 cents.

  • SSD vs. HDD Speed

This is where SSDs shine. An SSD-equipped PC will boot in far less than a minute, often in just seconds. A hard drive requires time to speed up to operating specs, and it will continue to be slower than an SSD during normal use. A PC or Mac with SSD boots faster, launches and runs apps faster, and transfers files faster. Whether you’re using your computer for fun, school, or business, the extra speed may be the difference between finishing on time and being late.

A secondary issue to this: fragmentation. Because of their rotary recording surfaces, hard drives work best with larger files that are laid down in contiguous blocks. That way, the drive head can start and end its read in one continuous motion. When hard drives start to fill up, bits of large files end up scattered around the disk platter, causing the drive to suffer from what’s called “fragmentation.”

While read/write algorithms have improved to the point that the effect is minimized, hard drives can still become fragmented to the point of affecting performance. SSDs can’t, however, because the lack of a physical read head means data can be stored anywhere without penalty. This contributes to SSDs’ inherently faster nature.

  • SSD vs. HDD Reliability and Durability

An SSD has no moving parts, so it is more likely to keep your data safe in the event you drop your laptop bag or your system gets shaken while it’s operating. Most hard drives park their read/write heads when the system is off, but when they are working, the heads are flying over the drive platter at a distance of a few nanometers. Besides, even parking brakes have limits. If you’re rough on your equipment, an SSD is recommended.

  • SSD vs. HDD Noise, Power, and Lifespan

Even the quietest hard drive will emit a bit of noise when it is in use. (The drive platters spin and the read arm ticks back and forth.) Faster hard drives will tend to make more noise than those that are slower. SSDs make no noise at all; they’re non-mechanical.

Plus, an SSD doesn’t have to expend electricity spinning up a platter from a standstill. Consequently, none of the energy consumed by the SSD is wasted as friction or noise, rendering them more efficient. On a desktop or a server, that will lead to a lower energy bill. On a laptop or tablet, you’ll be able to eke out more minutes (or hours) of battery life.

Then there’s the issue of longevity. While it is true that SSDs wear out over time (each cell in a flash-memory bank can be written to and erased a limited number of times, measured by SSD makers as a “terabytes written” or TBW rating), thanks to TRIM command technology that dynamically optimizes these read/write cycles, you’re more likely to discard the system for obsolescence before you start running into reading/write errors with an SSD.

If you’re really worried, several tools can let you know if you’re approaching the drive’s rated end of life. Eventually, hard drives will wear out from constant use, as well, since they use physical recording methods. Longevity is a wash when it’s separated from travel and ruggedness concerns.


Want to make your computer experience faster, including a boot time of fewer than 15 seconds, loading programs faster, and playing your game sooner? Use an SSD. Want more storage space because you have a lot of digital games or photos, or need a lot of storage for the media server on your NAS? Choose a hard drive (HDD).