SSD vs. HDD: What's the Difference?

Until recently, PC buyers had very little choice about what kind of storage to get in a laptop or desktop. If you bought an ultraportable, you likely had a solid-state drive (SSD) as the primary drive (C: on Windows, Macintosh HD on a Mac). Every other desktop or laptop form factor had a hard disk drive (HDD). Now, you can configure your system with either an HDD or SSD, or in some cases both. But how do you choose? We explain the differences between SSDs and HDDs (or hard drives), and walk you through the advantages and disadvantage of both to help you decide.

HDD and SSD Explained
The traditional spinning hard drive is the basic nonvolatile storage on a computer. That is, information on it doesn’t “go away” when you turn off the system, as is true of data stored in RAM. A hard drives is essentially a metal platter with a magnetic coating that stores your data, whether weather reports from the last century, a high-definition copy of the Star Wars trilogy, or your digital music collection. A read/write head on an arm accesses the data while the platters are spinning.

An SSD does functionally everything a hard drive does, but data is instead stored on interconnected flash memory chips that retain the data even when there’s no power present. The chips can either be permanently installed on the system’s motherboard (as on some small laptops and ultrabooks), on a PCI Express (PCIe) card (in some high-end workstations), or in a box that’s sized, shaped, and wired to slot in for a laptop or desktop’s hard drive (common on everything else). These flash memory chips are of a different type than is used in USB thumb drives, and are typically faster and more reliable. SSDs are consequently more expensive than USB thumb drives of the same capacities.

Note: We’ll be talking primarily about internal drives in this story, but almost everything applies to external hard drives as well. External drives come in both large desktop and compact portable form factors, and SSDs are gradually becoming a larger part of the external market.

A History of HDDs and SSDs
Hard drive technology is relatively ancient (in terms of computer history, anyway). There are well-known pictures of the infamous IBM 350 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, in the physical space that could hold two commercial refrigerators. The IBM 350 was only utilized by government and industrial users, and was obsolete by 1969. Ain’t progress wonderful? The PC hard drive form factor standardized at 5.25 inches in the early 1980s, with the 3.5-inch desktop-class and 2.5-inch notebook-class drives coming soon thereafter. The internal cable interface has changed from serial to IDE (now frequently called parallel ATA, or PATA) to SCSI to serial ATA (SATA) over the years, but each essentially does the same thing: connect the hard drive to the PC’s motherboard so your data can be processed. Today’s 2.5- and 3.5-inch drives mainly use SATA interfaces (at least on most PCs and Macs), though some high-speed SSDs use the faster PCIe interface instead. Capacities have grown from multiple megabytes to multiple terabytes, more than a million-fold increase. Current 3.5-inch hard drives have capacities as high as 10TB, with 2.5-inch drives maxing out at 4TB.

275The SSD has a much shorter history. There was always an infatuation with nonmoving storage from the beginning of personal computing, with technologies like bubble memory flashing (pun intended) and dying 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 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 low-end Eee PC units and the XO-1 were permanently soldered to the motherboard. As netbooks, ultrabooks, and other ultraportable laptop PCs became more capable, SSD capacities increased and eventually standardized on the 2.5-inch notebook form factor. This way, you could pop a 2.5-inch hard drive out of your laptop or desktop and replace it easily with an SSD. Other form factors emerged, like the mSATA Mini PCIe SSD card, M.2 SSD in SATA and PCIe variants, and the DIMM-like solid-state Flash Storage in the Apple MacBook Air and MacBook Pro, but today many SSDs still use the 2.5-inch form factor. The 2.5-inch SSD capacity currently tops out at 4TB, but a 16TB version was recently released by Samsung for enterprise devices like servers.

Advantages and Disadvantages
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 feature set. How do they differ, and why would you want to get one over the other?

Price: SSDs are more expensive than hard drives in terms of dollar per gigabyte. A 1TB internal 2.5-inch hard drive costs about $50, but as of this writing, an SSD of the same capacity and form factor starts at $220. That translates into 5 cents per gigabyte for the hard drive and 22 cents per gigabyte for the SSD. Since hard drives use older, more established technology, they will remain less expensive for the near future. Those extra hundreds for the SSD may push your system price over budget.

Maximum and Common Capacity: Although SSD units top out at 4TB, those are still rare and expensive. You’re more likely to find 500GB to 1TB units as primary drives in systems. While 500GB is considered a “base” hard drive in 2016, pricing concerns can push that down to 128GB for lower-priced SSD-based systems. Multimedia users will require even more, with 1TB to 4TB drives common in high-end systems. Basically, the more storage capacity, the more stuff you can keep on your PC. Cloud-based (Internet) storage may be good for housing files you plan to share among your phone, tablet, and PC, but local storage is less expensive, and you only have to buy it once.

Solid State Drive

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

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, large files can become scattered around the disk platter, causing the drive to suffer from what’s called fragmentation. W