Comparison Kingston A400 SA400S37/240G 240 GB vs WD Green SSD M.2 WDS240G2G0B 240 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 type of the main memory of the drive determines the features of the distribution of information over hardware cells and the physical features of the cells themselves.

— MLC. Multi Level Cell memory based on multi-level cells, each of which contains several signal levels. MLC memory cells store 2 bits of information. Has optimum indicators of reliability, power consumption and productivity. Until recently, the technology was popular in entry-level and mid-range SSD modules, now it is gradually being replaced by more advanced options in the manner of TLC or 3D MLC.

— TLC. The evolution of MLC technology. One Flash Memory Triple Level Cell can store 3 bits of information. Such a recording density somewhat increases the likelihood of errors compared to MLC, in addition, TLC memory is considered less durable. A positive feature of the nature of this technology is its affordable cost, and various design tricks can be used to improve reliability in SSDs with TLC memory.

— 3D NAND. In a 3D NAND structure, several layers of memory cells are arranged vertically, and interconnections are organized between them. This provides greater storage capacity without increasing the physical size of the drive and improves memory performance due to shorter connections for each memory cell. In SSD drives, 3D NAND memory can use MLC, TLC or QLC chips - more details...about them are described in the corresponding help paragraphs.

— 3D MLC NAND. MLC-memory has a multilayer structure — its cells are placed on the board not in one level, but in several "floors". As a result, manufacturers have achieved an increase in storage capacity without a noticeable increase in size. Also, 3D MLC NAND memory is characterized by higher reliability than the original MLC (see the relevant paragraph), at a lower manufacturing cost.

— 3D TLC NAND. "Three-dimensional" modification of the TLC technology (see the relevant paragraph) with the placement of memory cells on the board in several layers. This arrangement allows you to achieve higher capacity with smaller sizes of the drives themselves. In production, such memory is simpler and cheaper than a single-layer one.

— 3D QLC NAND. Quad Level Cell flash type with 4 bits of data in each cell. The technology is designed to make SSDs with large volumes widely available and finally retire traditional HDDs. In the 3D QLC NAND configuration, the memory is built according to a “multi-level” scheme with the placement of cells on the board in several layers. "Three-dimensional" structure reduces the cost of production of memory modules and allows you to increase the volume of drives without compromising their weight and size component.

— 3D XPoint. A fundamentally new type of memory, radically different from traditional NAND. In such drives, memory cells and selectors are located at the intersections of perpendicular rows of conductive tracks. The mechanism for recording information in cells is based on changing the resistance of the material without the use of transistors. 3D XPoint memory is simple and inexpensive to produce, and offers much better speed and durability. The prefix "3D" in the name of the technology says that the cells on the crystal are placed in several layers. The first generation of 3D XPoint received a two-layer structure and was made using a 20-nanometer process technology.

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 highest data exchange rate with a computer (or other external device) that the drive can provide in read mode; in other words — the highest speed of information output from the drive to an external device. This speed is limited both by the connection interface (see "Connector"), and by the characteristics of the device of the SSD itself. Its values can vary from 100 – 500 MB / s in the slowest models to 3 Gb / s and higher in the most advanced ones.

The IOPS provided by the drive in write mode.

The term IOPS refers to the highest number of I / O operations that an SSD module can perform per second, in this case, when writing data. By this indicator, the speed of the drive is often evaluated; however, this is not always true. Firstly, the IOPS values of different manufacturers can be measured in different ways — by the maximum value, by average, by random write, by sequential write, etc. Secondly, the benefits of high IOPS become noticeable only with some specific operations — in in particular, the simultaneous copying of numerous files. In addition, in fact, the speed of the drive may be limited by the system to which it is connected. In light of all this, it is generally acceptable to compare different SSD modules by IOPS, but the real difference in performance is likely not to be as noticeable as the difference in numbers.

As for specific values, for the write mode with IOPS up to 50K is considered relatively modest, 50 – 100K — medium, more than 100K — high.

The IOPS provided by the drive in read mode.

The term IOPS refers to the maximum number of I / O operations that an SSD module can perform per second, in this case, when reading data from it. By this indicator, the speed of the drive is often evaluated; however, this is not always true. Firstly, the IOPS values of different manufacturers can be measured in different ways — by the maximum value, by the average, etc. Secondly, the advantages of high IOPS become noticeable only with some specific operations — in particular, when copying numerous files at the same time. In addition, in fact, the speed of the drive may be limited by the system to which it is connected. In light of all this, it is generally acceptable to compare different SSD modules by IOPS, but the real difference in performance is likely not to be as noticeable as the difference in numbers.

For modern SSDs in read mode, an IOPS value of less than 50K is considered a very limited indicator, in most models this parameter lies in the range of 50 – 100K, but there are also higher numbers.