January 12, 2022

The Samsung SSD 980

When building a gaming or high-end desktop (HEDT) PC, a crucial component one cannot do without is permanent storage, usually in the form of a hard drive or solid-state drive (SSD). Today, the SSD is fast supplanting the hard drive as the main form of storage media in both laptops and desktops, as SSD storage capacity has increased while prices have come down.

Deciding on the best SSD for your particular PC build is not as difficult a task as choosing some of the other components that make up an HEDT computer. However, there are still some SSD specifications to be aware of before picking an SSD to fit your needs.

In this overview of SSDs, we focus our attention primarily on the latest type of solid-state drive, the M.2 NVMe SSD. We identify the important characteristics to look at when buying this advanced SSD technology, while at the same time, comparing some of the popular SSD choices available on the market today.

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Types of SSD

Types of SSD

SSDs come in a variety of different forms. One of the major differentiating factors between them is the type of physical connector used to connect them to the motherboard for data transfer. Today, older SSDs use a SATA data connector identical to those used by hard disk drives. Like hard drives, these SATA SSDs will connect via a SATA cable and be installed in locations within the PC case separate from the motherboard. These SATA SSDs naturally use the SATA bus to transfer data. 

More recent SSD technology makes use of the M.2 connector which is a smaller physical interface than the SATA connector (it was designed as a direct replacement for the mini-SATA (mSATA) connector) and connects directly to an SSD without the need for a cable. As a result, M.2 SSDs are installed directly onto the motherboard.

Importantly, however, M.2 SSDs are divided up into those that still operate via the SATA bus (M.2 SATA SSDs) and those that make use of the faster PCI-express bus (M.2 PCIe SSDs) for data transfer. Moreover, M.2 PCIe SSDs can be further subdivided into those that still use the AHCI driver, which was originally designed for SATA bus-based data transfer, and those that use the newer and faster NVMe driver.

Duagram showing the relationships between types of SSDs

Since most of us will only be interested in getting the latest solid-state drive technology, we are only going to concentrate here on the final type of SSD. This means the M.2 SSD which uses the PCIe bus and operates using the NVMe driver for data transfer. This most recent category of SSD is often abbreviated as M.2 PCIe NVMe SSDs or, more succinctly, as M.2 NVMe SSDs.


Popular M.2 NVMe SSDs (1TB)

SSD PCIe
Generation
Sequential
Read Speed
(MB/s)
Sequential
Write Speed
(MB/s)
NAND
Type
Endurance
Integral
M Series
Gen 320001600TLC450 TBW
Kingston NV1
Gen 321001700QLC240 TBW
Crucial P2
Gen 324001800QLC **300 TBW
WD Blue SN550
Gen 324001950TLC600 TBW
WD Green SN350
Gen 332002500QLC100 TBW
Acer FA100
Gen 333002700TLC600 TBW
Crucial P5
Gen 334003000TLC600 TBW
WD Blue SN570
Gen 335003000TLC600 TBW
Samsung 980
Gen 335003000TLC600 TBW
Samsung 970
EVO Plus
Gen 335003300TLC600 TBW
WD_BLACK™
SN750 SE
Gen 436002830TLC600 TBW
Corsair MP600
CORE
Gen 447001950QLC225 TBW
Corsair MP600
Gen 449504250TLC1800 TBW
Crucial P5 Plus
Gen 466005000TLC600 TBW
Samsung 980 PRO
Gen 470005000TLC600 TBW
WD_BLACK™
SN850
Gen 470005300TLC600 TBW
** originally TLC but has since been changed to QLC

M.2 NVMe SSD specifications

Read/Write speeds

Probably the most important specification of any storage drive is the speed at which it can read and write data. M.2 NVMe SSDs read and write data at phenomenal speeds especially when compared to the traditional hard drive. As it is for hard drives, read and write speeds on SSDs come in two different forms: Sequential and Random.

Sequential

Sequential read/write speeds are the speeds at which the data storage drive can be read from or be written to in a contiguous manner, usually in the form of one or a few large data files. In the real world, this is similar to transferring large amounts of data in one go between storage drives. This makes this metric less applicable to real-life computer use where it is not often that one copies large volumes of data continuously. Unfortunately, most SSD manufacturers rate their drives using only sequential read/write speed information, as the comparatively larger values obtained with this metric are usually more impressive to look at than those from the Random read/write data. Importantly, however, sequential read/write speeds may be more applicable to certain users, such as video editors, who typically deal with moving very large video files regularly.

Random

Random read/write speeds represent the reading from and writing to the storage drive of relatively small but numerous data files that are randomly accessed. This metric is most akin to how storage drives are used by the majority of computer users and by a computer's operating system when an SSD is configured as the OS drive. Unfortunately, manufacturers rarely (if ever) provide Random read/write specifications for their storage drives making it difficult to compare drive performance fully.  

Benchmarks

In addition to looking over read/write speed information provided by manufacturers, another way to rate the performance of SSDs against each other is to look at user benchmarks. A useful site to compare the performance of today's SSDs is ssd.userbenchmark.com which compares the performance characteristics of a range of SSDs derived from real-life users.

SSD benchmarks website

SSD benchmarks website: ssd.userbenchmark.com

Once you have determined how well an SSD performs against its peers and you have found an M.2 NVMe SSD or two that meets your performance needs, it is then time to examine the other technical aspects of SSDs to determine if they truly are suitable.

PCIe 3.0 vs PCIe 4.0

PCI Express logo

At the time of writing, the data transfer standard, PCI-express (PCIe), when it specifically concerns SSDs, is in the midst of transitioning from PCIe version 3 to PCIe version 4 as the dominant version at M.2 interfaces. Consequently, higher-end more expensive computer motherboards will employ PCIe version 4, while at the medium-to-low end of the cost spectrum, PCIe 3.0 currently remains the more dominant format. Note, however, that this is different from the dominant PCIe version on motherboards used specifically by CPUs, which is currently at version 4 and is just beginning to move to PCIe version 5.

Obviously, going for the latest version of any standard is always going to be the preferred option. However, when it comes to SSDs, although there are some SSD performance benefits gained with PCIe version 4, the question remains as to whether those limited benefits outweigh the extra cost of the higher standard.

In any case, the motherboard's SSD hardware must be able to support PCIe version 4 if you are to use a PCIe 4.0-capable SSD at its full speed and full potential. Although a PCIe 4.0 SSD will work within PCIe 3.0-rated slot (and vice-versa), it will always do so at the lower version of the standard, negating any performance benefits associated with having a version 4.0 device.

Endurance

TBW

Another important characteristic of SSDs to pay attention to is Endurance. Solid-state drives have a limited lifespan of several years, depending on how much they are used. That is because the memory modules that they are comprised of can only be written to a set number of times before they start to become unreliable. Different SSD brands, models, and memory capacities will have different total amounts of data that can be written to them over time. As a consequence, one needs a way to compare different drives for longevity.

There are a couple of different ways to measure SSD expected lifespan, but the simplest metric and the one that practically all SSD manufacturers use is the number of TeraBytes Written or TBW. As its name suggests, TBW represents the cumulative total amount of data that an SSD would be expected to be written to before there was any possibility of it running into reliability issues. Importantly, however, the TBW number typically represents the amount of data the manufacturer warranties the device to be able to handle over its lifetime. In real-world use, SSDs will typically exceed these values before anything actually starts to fail.

To get a better idea of what TBW actually means for an SSD, the table below shows some common SSD TBW values and the theoretical maximum number of gigabytes per day that could be written to an SSD if it is to last at least 10 years.  

Terabytes

Written (TBW)

The daily amount of data that could be 

written to an SSD over 10 years

100 TBW

27 gigabytes per day

225 TBW

62 gigabytes per day

240 TBW

66 gigabytes per day

300 TBW

82 gigabytes per day

450 TBW

123 gigabytes per day

600 TBW

164 gigabytes per day

Clearly, for just about any common SSD TBW value, the vast majority of computer users will never exceed writing these amounts of data to an SSD each and every day! Consequently, most SSDs will typically last at least the lifetime of a typical PC.

NAND flash type

NAND

flash

Number of

bits per cell

SLC

1

MLC

2

TLC

3

QLC

4

PLC

5

NAND flash, which makes up the memory cells found in SSDs, currently exists in several forms including Single-Level Cell (SLC), Multi-Level Cell (MLC), Triple-Level Cell (TLC), Quad-Level Cell (QLC), and Penta-Level Cell (PLC).

Without going into too much detail about what differentiates the different types of NAND flash, suffice it to say that the different names refer to the number of bits that can be stored in each cell of memory.

Over time, manufacturers have been able to store more and more bits in each cell which has allowed the average capacity of SSDs to rise while keeping prices low. Unfortunately, as you increase the number of bits per cell, memory cell longevity falls as each bit is represented by a smaller physical area within the memory cell and the cell itself is accessed more often.

Today the majority of NAND flash is of the TLC (sometimes referred to as '3-bit MLC') and QLC varieties, and you will be hard-pressed to find consumer SSDs based on SLC and MLC NAND flash. When choosing an SSD of a certain capacity, choosing one with a lower number of bits per cell is the way to go. Therefore, a TLC-based SSD will almost always have a longer lifespan than a QLC equivalent and should be the preferred NAND flash type.

So ultimately what NAND flash type comes down to is in determining SSD longevity. However, we already have a better technical specification that defines SSD lifespan, namely Endurance. And it should come as no surprise that the TBW number of an SSD inversely correlates with the number of bits per cell that it uses. Therefore, as you can see in the 1TB M.2 NVMe SSD table on this page, TLC-based SSDs tend to have a higher TBW figure than QLC-based ones. Consequently, when choosing an SSD, it is better to concentrate first on its Endurance value, before just confirming that its NAND flash type is of the preferred TLC type.

SLC cache

Today's SSDs also have a special type of very fast onboard memory or cache which is usually comprised of SLC, hence the name, SLC cache. This cache briefly stores any data sent to the SSD until the SSD is ready to write it to its more permanent memory. Therefore, the size of this cache can have a disproportionate effect on the SSD sequential write speeds which will drop significantly when the cache is full.

Unfortunately, manufacturers do not always make clear how big the SLC cache is on their SSDs, leaving it to reviewers and SSD testers to find out experimentally. Fortunately, however, as most computer users will not be transferring large amounts of data on a regular basis, as is typical of sequential write speeds, the size of the cache of a given SSD should not be noticed too much. If however, you are the type of user that moves a lot of data to and from an SSD often, then analysing SSD cache capacity is a must.

Form factors

SSDs can come in a variety of different form factors. However, your typical M.2 NVMe SSD will be 22 mm in width and either 30 mm, 42 mm, 60 mm, 80 mm, 110 mm in length. Consequently, these SSDs are designated as having a size format of 2230, 2242, 2260, 2280, or 22110, respectively. To choose the right format for your build, consult your motherboard technical specifications or manual to determine which form factor(s) are compatible.

M.2 specifications for the Gigabyte Aorus Elite AX motherboard

M.2 specifications on the Gigabyte Z590 Aorus Elite AX motherboard (arrow pointing to compatible form factors)

Types of M.2 key

SSD M-key

M-key

Finally, a word about the M.2 key type, which refers to the arrangements of data pins and gaps on the connecting interface. The M.2 standard specifies several different key types but currently, you are only likely to encounter three of them when it comes to SSDs: the M-key, the B+M key and the B-key. Furthermore, when it comes to the latest SSD technology, M.2 NVMe SSDs, they are almost always M-keyed as the M-key supports 4 data lanes on the PCIe bus, which is required for the higher data transfer speeds that M.2 NVMe SSDs are capable of. Anyway, to be sure that you have the right hardware to accommodate an M.2 SSD, consult your motherboard technical specifications to verify the key type of its M.2 slots.


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