How to choose an SSD
If you are building a powerful computer or want to speed up the old one, you will need an SSD. Finally, the cost of these storage devices has fallen so much that they can be considered as a reasonable alternative to hard disk drives (HDD).
The SSD features listed below will help you choose the best model that is compatible with your computer and suits your needs.
Types and form factor of SSD drives
SSD 2.5" - this form factor is the most common. It looks like a small box of regular hard drive. Format 2.5" is the cheapest, but their speed is enough for most users (see photo).
This form factor can be installed on any desktop or laptop computer, that has a free 2.5-inch drive Bay. If your system only has space for an old 3.5 "hard drive, you can also insert a 2.5" model into it. But in this case, look for a model that comes with a special lock or buys it separately.
Like all modern hard drives, 2.5-inch models are connected to the motherboard via SATA2/3 interface. This connection provides a bandwidth of up to 600Mbps. If you have an old motherboard with SATA2 connector, you can connect 2.5" SSD, but the speed of the him will be limited by the old version of the interface - up to 300Mbps.
A standard mSATA designed for laptops and other compact PCs that lacked space for a 2.5-inch device. The corresponding interface is quite rare today, in no small part due to the fact that mSATA is still running at a relatively low SATA speed. Today, the mSATA standard can be considered outdated - it gave way to the standard of M.2.
M.2 - is a more compact form factor, thanks to which it is suitable even for the most thin laptops, in which there is no space for the 2.5 inch device. It looks like an oblong plate mounted in a separate compartment and directly on the motherboard (see photo). Or installed through a special HHHL adapter into the PCIe-slot of the motherboard. On sale, you can also find devices execution in the form factor HHHL or even larger form factor FHHL.
To connect to the motherboard each disk uses one of two interfaces: SATA 3 or via PCIe line. PCIe is several times faster than SATA 3. If you choose the first one, you should consider a few things: the version of the interface and the number of lines connected to the data connector.
The higher the PCIe version, the higher the bandwidth (data rate) of the interface. There are two versions: PCIe 2.0 (up to 1.6 GB/s) and PCIe 3.0 (up to 3.2 GB/s). The more data lines connected to the SSD connector, the higher its bandwidth. The maximum number of lines in SD is four, in this case its interface is designated as PCIe x4 in the model description. If there are only two lines, then - PCIe x2.
Each connector on the motherboard designed to connect the drives of format M. 2, has a special notch (key) is one of two types: B or M. At the same time, the connector on each disk M.2 has two cutouts B+M or at least one of the two keys: B or M (see photo).
Considering the physical compatibility of the connector, it is not enough for the SSD to fit your motherboard. The fact is that the drive connector may not support the logical interface, that is used in your motherboard slot. For example, the motherboard in The PCIe x2 socket uses the "B" key, but there is an SSD "M2 SATA", which also use the "B" key! Of course, if you connect such a disk to the motherboard with PCIe x2 connector - it will not work!
Therefore, when you are dealing with keys, find out what Protocol is implemented in connector M.2 on your Board. It may be SATA3, PCIe x2 or PCIe x4. Then select the model with the same interface. Types of keys usually identify connectors and slots. In addition, all the necessary information can be found in the documents on the motherboard and disk.
Pay attention to the data transfer mechanism. The old storage devices uses the AHCI protocol, which with the advent of faster drives it ceases to cope with its task (does not allow to use the maximum speed characteristics of the drives). A new protocol, NVMe, has been released to address this issue. It provides higher speed, requires less CPU resources during read/write operations, becomes significantly less latency. For your SSD to work under this protocol, pay attention to whether your motherboard supports this technology.
Another nuance, which determines the compatibility of the drive with the motherboard, is its length. In the specifications of most motherboards you can find numbers 2260, 2280 and 22110. The first two digits in each, indicate the width of the disk support. It is the same for all M.2 and equals 22 mm.. The next two digits is the length, so most motherboards are compatible with 60, 80 and 110 mm..
Types of memory SSD drives
Existing SSD today use four types of NAND flash memory such as SLC, MLC, TLC and 3D NAND.
SLC (single-level cell) is a single-level cell. Contains one bit of data and can only take two values. It has high write speed and number of P/E cycles. In principle, this type of memory is used for high-level servers, as the cost of SLC is very high.
MLC (multi-level cell) is a two-level cell. Contains two bits of data and accepts four combinations of values. MLC NAND has less endurance and fewer Program/Erase (P/E) cycles, so it's a great solution for work platforms and home use. The cost is much lower compared to SLC SSD. eMLC (Enterprise Multi Level Cell) similar to the structure of cells in MLC, but has an increased resource for a number of cycles P/E, the reliability of the MLC cell takes an intermediate value between SLC and MLC. The cost is not much higher than the cost of MLC and is used mainly on middle class workstations and servers.
TLC (three-level cell) a three-level cell with a higher density. Contains three bits of data and takes eight values, which ultimately results in less endurance, slower read/write speed. Compared to SLC and MLC, it has the lowest P/E cycles. In the past, TLC/NAND memory Was used mainly in conventional flash drives, but today, thanks to the improvement of production technologies, this type of memory can be used in standard SSD-devices.
All the first three types of memory cells belong to the flat two-dimensional NAND memory. Their main drawback is that it is technologically impossible to constantly increase the density of cells by reducing the size of the crystal. NAND 3D memory was developed to solve this problem - 3D V-NAND (or V-NAND). Where cells are located in several layers, which allows you to create a large capacity SSD. According to the developers, the reliability and performance of 3D V-NAND flash memory is higher than that of NAND.
On March 20, 2017, Intel Corporation introduced a line of drives based on innovative 3D XPoint memory. Has been called - Optane SSD DC P4800X (PCI Express, format HHHL) (Pic). The devices use 128-Gigabit 20-nanometer 3D xpoint chips, have a capacity of 375 or 750 GB and are equipped with an Intel NVMe ASIC controller, which is able to control four crystals on one channel simultaneously, which provides phenomenal performance on all parameters. But do not rush to place orders: the recommended price of Optane is 1520 US dollars.
Additional recommendations for choosing SSD drives
There are several important characteristics to determine the life of an SSD. A TBW (Total Bytes Written) resource that reflects how much data can be written to disk. And DWPD (Drive Writes Per Day), which shows the number of valid overwrites per day.
IOPS is an indicator of operations per second of data input and output. It is one of the key parameters in measuring the performance of storage systems: HDD, SSD, SAN.
In addition to the memory type, the performance of the SSD is affected by other characteristics, such as the model of the controller installed on the disk and its firmware. But these data often do not even indicate in the description. Instead, they are the final indicators of read and write speed, which is easier for the buyer to navigate. So, choosing between two SSD, ceteris paribus, hold the disc where the stated rate above. Remember that the manufacturer specifies only theoretically possible speeds. In practice, they are always lower than indicated.
For all its advantages, SSD have disadvantages: a limited number of rewritable items, so they are often used in conjunction with the hard drive only as an "accelerator" of the operating system and do not work with data. In addition, the cost of SSD is much higher than HDD.
When choosing an SSD drive, you need to pay attention to the speed of writing and reading, and an important indicator is the speed of random writing. But it makes no sense to buy an SSD drive with a write and read speed of more than 600 MB/s, if its connection is planned through the SATA interface, this interface is simply not capable of high bandwidth.