Comparison Crucial BX500 CT120BX500SSD1 120 GB vs WD Green SSD M.2 WDS120G2G0B 120 GB

The form factor in which the drive is made. This characteristic determines the size and shape of the module, and in many cases also the connection interface. At the same time, it should be noted that for external SSDs (see "Type") the form factor is a secondary parameter, only the overall dimensions of the case depend on it (and even then very approximately). Therefore, you should pay attention to this moment first of all when choosing an internal SSD — such a drive must correspond to the form factor of the seat for it, otherwise a normal installation will be impossible.

Here are some of the more popular options:

— 2.5 ". One of the most common form factors for internal SSDs. Initially, 2.5" drives were used in laptops, but nowadays the corresponding slots are also found in most desktop PCs. Anyway, modules of this form factor can be installed in different ways: some are mounted in separate slots similar to hard drives, others (under the U.2 interface, see "Connector") are inserted directly into motherboard connectors.

— M.2. A form factor used mainly in high-end internal drives that combine miniature size and significant volumes. It uses its own standard connection connector, so this connector is not separately indicated in the specifications. Note that the M.2 standard combines two data transfer formats at once — SATA and PCI-E, and the drive usually supports only one of the...m; see "M.2 interface" for details. Anyway, due to their small dimensions, such modules are suitable for both desktop PCs and laptops.

— mini-SATA (mSATA). Miniature form factor of internal drives, the ideological predecessor of M.2. It was originally developed for netbooks and ultra-compact laptops, but nowadays you can also find desktop PCs with mSATA connectors on motherboards. However, due to the emergence and development of more advanced options, this form factor is gradually falling into disuse.

— PCI-E card(HHHL). Drives made in the form of expansion cards and plugged into PCI-E slots (just like external video cards, sound cards, etc.). The HHHL marking means half length and half height, so these modules are suitable not only for full-sized PCs, but also for more compact systems, such as nettops and even some laptops. The PCI-E interface allows you to achieve good data transfer speeds, moreover, NVMe is implemented through it (see below). On the other hand, these features are also available in more advanced and compact form factors, in particular M.2. Therefore, there are few SSD modules in the PCI-E card format nowadays on the market.

— 1.8 ". The form factor of miniature drives, originally created for ultra-compact laptops. However, nowadays SSD modules of this format can be found extremely rarely, and these are mainly external models. This is due to the emergence of more convenient and advanced forms factors for internal use, such as M.2 described above.

— 3.5". The largest form factor of modern SSDs — the size of such a module is comparable to a traditional desktop PC hard drive. Nowadays, it has practically fallen into disuse due to bulkiness and the absence of any noticeable advantages over smaller solutions .

Connection interface supported by an M.2 drive (see Form Factor).

All such drives use a standard hardware connector, however, different electrical (logical) interfaces can be implemented through this connector — either SATA (usually SATA 3), or PCI-E (most often in PCI-E 3.0 2x, PCI-E 3.0 4x, PCI-E 4.0 4x, PCI-E 5.0 4x). The M.2 connector on the motherboard must support the appropriate interface — otherwise the normal operation of the SSD will not be possible. Let's consider each option in more detail.

SATA 3 connectivity provides data transfer rates up to 5.9 Gbps (approx. 600 Mbps); it is considered a very simple option and is used mainly in low-cost M.2 modules. This is due to the fact that this interface was originally created for hard drives, and for faster SSD drives, its capabilities may no longer be enough.

In turn, the PCI-E interface provides higher connection speeds and allows the implementation of special technologies like NVMe (see below). The designation of such an interface indicates its version and the number of lines – for example, PCI-E 3.0 2x means version 3 with two data lines. By this designation you can determine the maximum connection speed: PCI-E version 3.0 gives just under 1 GBps per line, version 4.0 – twice as much (up to 2 GBps), 5.0 – twice as much a...s the “four” (almost 4 GBps). Thus, for example, for PCI-E 5.0 4x the maximum data transfer speed will be about 15 GBps (4 lanes of almost 4 GBps). However, we note that newer and faster drives can be connected to earlier and slower M.2 connectors – except that the data transfer speed will be limited by the capabilities of the connector.

The connection connector(s) used in the drive. Note that for outdoor models (see "Type"), here, usually, the connector on the case of the drive itself is indicated; the ability to connect to a particular jack on a PC (or other device) depends mainly on the availability of appropriate cables. The exception is models with a non-removable wire — they are talking about a plug on such a wire.

Some form factors — for example, M.2 — use their own standard connector, so this parameter is not specified for such models. In other cases, the connectors can be conditionally divided into external and internal — depending on the type of drives (see above). In internal modules, in addition to the same M.2, you can find SATA 3, U.2 and SAS interfaces. External devices mainly use different types of USB — the classic USB connector (versions 3.2 gen1 or 3.2 gen2) or USB-C (versions 3.2 gen1, 3.2 gen2, 3.2 gen2x2 or USB4). In addition, there are solutions with the Thunderbolt interface (usually versions v2 or v3). Let's take a closer look at these options:

— SATA 3. The third version of the SATA interface, providing data transfer rates up to 5.9 Gbps...(about 600 MB / s). By SSD standards, this speed is low, since SATA was originally developed for hard drives and was not intended to be used with high-speed solid-state memory. Therefore, such a connection can be found mainly in low-cost and outdated internal drives.

— SAS. A standard designed as a high performance connection for server systems. Despite the emergence of more advanced interfaces, it is still found nowadays. Provides data transfer rates up to 22.5 Gbps (2.8 GB/s), depending on version.

— U.2. A connector specially designed for high-end internal drives in the 2.5 "form factor, mainly for server purposes. Actually, U.2 is the name of a specialized form factor (2.5", height 15 mm), and the connector is formally called SFF- 8639. Such modules are connected in the same way as PCI-E expansion cards (via the same bus), but they are smaller in size and can be hot-swapped.

— U.3. A three-interface connector based on the U.2 specification (see the relevant paragraph) and using the same SFF-8639 connector. The U.3 connector combines SAS, SATA and NVMe interfaces in one controller, allowing you to connect different types of drives through the same slot. U.3 provides separate pins for identifying a particular type of drive. The specification was created for internal 2.5" form factor drives. Such modules are miniature, hot-swappable, and support external control pulses.

— USB 3.2 gen1. Traditional full-size USB connector, compliant with version 3.2 gen1. This version (formerly known as 3.1 gen1 or 3.0) provides data rates up to 4.8 Gbps. It is compatible with other USB standards, except that the connection speed will be limited by the slowest version.

— USB 3.2 gen2. A traditional full size USB connector, corresponding to version 3.2 gen2 (previously known as 3.1 gen2 or simply 3.1). Operates at speeds up to 10 Gbps, otherwise the key features are similar to those described above USB 3.2 gen1

— USB-C 3.2 gen1. USB-C connector supporting 3.2 gen1. Recall that this version allows you to achieve speeds up to 4.8 Gbps. And USB-C is a relatively new type of USB connector, having a small size (slightly larger than microUSB), a symmetrical oval shape and a double-sided design. It is especially useful for external SSDs, given that such drives are getting smaller and smaller.

— USB-C 3.2 gen2. USB-C connector supporting version 3.2 gen2 connectivity — with data transfer rates up to 10 Gbps. However, such a drive will be able to work with slower USB ports — unless the speed will be limited by the capabilities of such a port. See above for details on the USB-C connector itself.

— USB-C 3.2 gen2x2. USB-C type connector supporting connection version 3.2 gen2x2. For more information about the connector itself, see above; and version 3.2 gen 2x2 (previously known as USB 3.2) allows to achieve speeds up to 20 Gbps — that is, twice as high as in the original 3.2 gen 2, hence the name. It is also worth noting that this version is implemented only through USB-C connectors and is not used in ports of earlier standards.

— USB4. A high-speed revision of the USB interface that uses only symmetrical USB type C connectors. Allows you to achieve data transfer rates of up to 40 Gbps (depending on the technologies and standards implemented in a particular port). The interface can support Thunderbolt v3 and v4, and is backward compatible with previous USB specifications, although devices with a full-size USB-A plug will require an adapter.

Model of the controller installed in the SSD.

The controller is a control circuit, which, in fact, ensures the exchange of information between the memory cells and the computer to which the drive is connected. The capabilities of a particular SSD module (in particular, read and write speed) largely depend on this particular scheme. Knowing the controller model, you can find detailed data on it and evaluate the capabilities of the drive. For simple everyday use, this information is usually not needed, but for professionals and enthusiasts (modders, overclockers) it can come in handy.

Nowadays, high-end controllers are produced mainly under such brands: InnoGrit, Maxio, Phison, Realtek, Silicon Motion, Samsung.

The highest speed in write mode characterizes the speed with which the module can receive information from a connected computer (or other external device). This speed is limited both by the connection interface (see "Connector"), and by the characteristics of the device of the SSD itself.

The drive's time between failures is the time that it is able to continuously work without failures and malfunctions; in other words — the operating time, after which there is a high probability of failures, and even failure of the module.

Usually, the characteristics indicate some average time derived from the results of conditional testing. Therefore, the actual value of this parameter may differ from the claimed one in one direction or another; however, in fact, this moment is not particularly significant. The fact is that for modern SSDs, the MTBF is estimated at millions of hours, and 1 million hours corresponds to more than 110 years — while we are talking about pure operating time. So, from a practical point of view, the durability of a drive is often limited by more specific parameters — TBW and DPWD (see below); and the manufacturer's warranty generally does not exceed several years. However, data on the MTBF in hours can also be useful when choosing: other things being equal, more time means more reliability and durability of the SSD as a whole.

The abbreviation TBW stands for drive time between failures, expressed in terabytes. In other words, this is the total amount of information that is guaranteed to be written (rewritten) to this module. This metric measures the overall reliability and lifespan of a drive—the higher the TBW, the longer the device will last, all other things being equal.

Note that knowing the TBW and the warranty period, you can calculate the number of rewrites per day (DWPD, see the relevant paragraph), if the manufacturer did not specify these data. To do this, use the formula: DWPD = TBW / (V * T * 365), where V is the drive capacity in terabytes, T is the warranty period (years). As for specific numbers, there are a lot of drives on the market with a relatively low TBW — up to 100 TB ; even these values are often sufficient for everyday use for a considerable amount of time. However, models with TBW at the level of 100 – 500 TB are more common. Values of 500 – 1000 TB can be classified as "above average", and in the most reliable solutions this figure is even higher.

The number of full overwrites per day allowed by the design of the drive, in other words, how many times a day the entire drive can be guaranteed to be overwritten without fear of failures.

This parameter describes the overall reliability and durability of the drive. It is similar in meaning to TBW (see the relevant paragraph), one value can even be converted to another, knowing the warranty period: TBW = DWPD*V*T*365, where V is the drive capacity in terabytes, and T is the warranty period in years . However, DWPD is somewhat more specific: it describes not only the total time between failures, but also the limit on the number of rewrites per day; if this limit is exceeded, the drive may fail earlier than specified in the warranty. However, even small DWPD values — 0.5 – 1 time per day, or even less than 0.5 times a day — often turn out to be sufficient not only for simple everyday use, but even for professional tasks. Higher rates — 1 – 2 times a day or more — are rare; at the same time, it can be both high-end and low-cost SSD modules.