Solid State Hard Drives

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Hard disk drives boast large capacities and, in most cases, good performance—but they’re still bound by the laws of physics. That means many fragile moving parts, and the armature constantly in motion to locate bits of information from specific areas of a spinning disk.

The alternative is a solid state drive (SSD), or solid state media, which improves on almost everything a hard disk can do. An SSD stores data in flash memory, so there’s no mechanical arm, no spinning platters, no sound, and no worry that a jostle might damage the disk. More important: the performance improvement is significant.

The tradeoff with SSDs is capacity, both in terms of cost per unit of storage and overall amount of storage. Solid-state storage is still expensive compared to traditional hard drives, so SSDs offer less capacity for the money. As of mid-2020, $100 can buy 1 to 4 TB of hard drive storage, but 500 GB to 1 TB of solid-state storage. SSD modules also max out at 8 TB, whereas single hard drives currently go up to 18 TB.

How SSDs Work

When a computer adds data to a standard disk, it locates a stretch of the platter marked as empty and writes the data in chunks. If an entire file does not fit in a continuous strip, pieces are written onto other areas where space is available.

An SSD stores data in memory cells. Although the file system will attempt to write data in contiguous cells, writing and retrieval is so quick that it’s not as important to keep all the bits of a file together.

Figure 3: Hard disks write data in contiguous strips when possible (left). SSDs can store bits in whichever cells are available without a noticeable performance decrease (right).

Surprisingly, the way solid-state memory manages its data leads to wear on the cells, which have a finite lifespan. When you delete a file on a spinning-platter disk, the operating system marks the areas of the disk’s surface that contained the file as available. New data can be simply written over the old data.

An SSD’s memory cells can’t just be overwritten. Instead, the system shuffles data around to open cells and erases the cells on which the deleted data resided (a process called garbage collection). Deleting data requires more electrical power that writing data, so the system erases cells in blocks.

Don’t worry, “finite” here translates to several years of normal usage. If you’re frequently writing and erasing vast amounts of data, such as when working with massive video files, the life expectancy of an SSD is shorter. Manufacturers measure SSD lifespan in TBW, or terabytes written. Larger capacities boast higher TBW because they contain more cells; a 1 TB SSD, for example, offers around 600 TBW.

SSD Types and Form Factors

In Macs with solid-state media built in (which is most of them now), the chips that make up the storage are connected directly to the logic board. That means you can’t swap an old drive out for a newer one, as is possible on other computers (and older models). So, if you’re in the market to buy a Mac with solid-state storage, it’s worth spending the extra money for more capacity at the outset.

If your Mac does contain a standard internal drive that you can access, the easiest option is to replace it with an SSD in a 2.5-inch enclosure These SSDs connect using the same SATA connector as standard drives.

Figure 4: Many SSDs, like the one on the right, are designed with the same dimensions as 2.5-inch mechanical drives for easy replacement.
Figure 4: Many SSDs, like the one on the right, are designed with the same dimensions as 2.5-inch mechanical drives for easy replacement.

Note: There’s always an exception, isn’t there? It is possible to replace or augment the SSD storage in the latest Mac Pro (introduced in 2019), even though the modules don’t share the same form factors as other SSDs. Because they’re cryptographically tied to the machine’s T2 chip, though, make sure you follow Apple’s directions to properly configure the installation.

In the last several years, a new SSD option has emerged for consumers. NVMe (Non-Volatile Memory Express) is physically smaller and much faster than most 2.5-inch SATA SSDs.

Figure 5: NVMe solid-state storage is small and fast.
NVMe solid-state storage is small and fast.

How fast? A typical SATA SSD maxes out at about 550 MBps, while NVMe can hit 3,000 MBps (3 GBps) and higher. That performance increase has less to do with the storage memory itself than the way the data is transferred. Instead of SATA, which was designed for standard hard drives, NVMe uses a much faster PCIe (PCI Express) bus, the same technology used for graphics cards and Thunderbolt. If you’re interested in which NVME drives are the best, you can review this blog post by Techstat, which lists the top 5 1tb nvme ssd drives available.

That sounds great, but for Mac owners, NVMe storage isn’t an easy option. Although Apple has used it in some iMac and MacBook Pro models, neither machine is easy to access. However, NVMe storage can be a good option for external storage by putting it in an enclosure with a USB 3 or Thunderbolt connector. (If you want to try your hand at improving an old iMac with NVMe storage, see the Macworld article Upgrading an older iMac’s PCIe SSD: Third-party solutions that save you beaucoup bucks, and of course consult iFixIt for guides to access various machines.)

Tip: An SSD in a 2.5-inch enclosure can be added to a desktop computer that has a 3.5-inch space. Purchase a bracket adapter, which typically costs $10 or so, to mount a 2.5-inch drive within the 3.5-inch bay.

Best Storage Tip of the Decade

Do you have an older computer that’s sputtering along slowly enough that you’re thinking of replacing it? If it has a traditional hard disk drive, consider installing an SSD in its place.

For several generations, I replaced my MacBook Pro models about every three years, but with my 2010 MacBook Pro, I replaced the 5400 rpm hard drive with an SSD. That doubled the machine’s life for me: I finally replaced it with a new MacBook Pro after six years when I decided it was time to take advantage of new-to-me technologies such as USB 3 and more advanced Bluetooth (for unlocking the computer using my Apple Watch, for example).

In fact, at one point I pulled out the optical drive and installed a second SSD in that bay, giving me 1 TB of SSD storage.