The general purpose of the pocket.
Note that for different types of such accessories (see above), a different division is used according to purpose. So, external pockets are divided into
portable and
stationary, and internal pockets are divided into laptop models,
PC chassis and
server solutions. For docking stations and cases, this parameter is not specified at all: the former initially assume stationary use, the latter, again, are portable by definition.
Here is a more detailed description of the options relevant for external pockets:
— Portable. Models designed for frequent moving from place to place and even for use on the go (for example, connecting to a laptop on the road). Most modern external pockets fall into this category — after all, initially external drives (which such pockets are an alternative to) are also made predominantly portable. The specific features of these accessories may vary, but they are all quite compact and designed for only one internal drive, and they receive energy from the same USB port they are connected to (see "Power").
— Stationary. External pockets designed to stay in one place all the time and do not involve frequent movement and use on the road. Such models are much less common than portable ones; most of them are rather l
...arge designs, designed to install 2 or more drives, and are often a kind of "NAS-server without networking". However, there are also models for 1 slot — they usually differ from portable counterparts in the presence of a stand that allows you to put the pocket vertically (so that it takes up less space on the table), and is powered by a power supply unit.
In turn, internal pockets for different purposes have the following specifics:
— For laptops. This type is usually designed to install 2.5" or M.2 form factor drives in the optical drive bay (CD / DVD) — due to the compact size of laptops, this is often the only possible way to install an additional drive.
— Chassis. Pockets designed for regular desktop PCs. Note that the term "chassis" traditionally refers to only one special kind of such pockets — the so-called Mobile Rack, colloquially known as "sled". The main function of such accessories is to provide the ability to quickly move drives from one case to another. To do this, the design provides for two parts: a base, which is mounted in a 5.25" slot on the case, and a removable cartridge, into which the drive is installed directly. To prevent theft or unauthorized physical access, the "sled" can be equipped with a lock that blocks the removal of the drive. Our time is used quite rarely, mainly when working with disk arrays, as well as in some other specific cases — for example, so that after the end of the working day you can take a disk with materials with you or hide it in a safe to ensure confidentiality.
Another kind of PC pockets are adapters for installing drives in non-standard seats. The classic case is the use of a 2.5" laptop drive in a 3.5" desktop case, but nowadays there is a more specific option — the use of an SSD M.2 drive as a PCI-E expansion card (for more details, see "Form factor") .
— For the server. Server systems most often have to deal with large volumes of information that require high reliability and/or speed of access. Thus, most pockets of this purpose are designed for several drives (from two to six) — this allows you to provide the necessary volumes and, if necessary, organize a RAID array of one or another level. At the same time, built-in support for RAID (see below) is not found in such devices — it is easier and more reasonable to organize it using the server itself. It is also worth noting that according to the method of installing disks, such pockets usually refer to “sleds” (see “Chassis” above) — this provides additional convenience, allowing, for example, quickly replacing a failed drive in a RAID array. Server pockets can use specialized connection interfaces like SAS, although traditional SATA is still more popular.The method of connecting a pocket with an installed drive to a computer, provided for in the design.
Note that this parameter is specified only in cases where the connection interface differs from the drive interface (see above). A similar feature is typical for all external models and docking stations (see "Type"): nowadays they most often use
USB 3.2 gen1, less often —
USB 2.0 or
USB-C of one version or another (see below). In internal solutions, the drive connector rarely differs from the pocket connector, although there are exceptions.
It is also worth mentioning that in external models, the connection method is usually determined by the type of bundled cable; moreover, such a cable is often made removable, with the possibility of replacing it with a “cord” with a different type of plug.
As for specific connection methods, here are their main features:
— USB 2.0. USB is used to connect external peripherals, including pockets; this is the most popular modern interface of this purpose. And version 2.0 is the oldest USB standard in use today. The possibilities of such a connection are very limited — in particular, the power supply through the connector is 2.5 W, and the maximum data transfer rate does not exceed 480 Mbps. This is noticeably slower than even SATA 2 (3 Gbps), not to mention SATA 3 (6Gb/s); so in general this stan
...dard is considered obsolete, and in pockets with this type of connection, the overall speed is limited just by the capabilities of USB 2.0. However, maintaining this interface is inexpensive; for simple tasks that are not associated with large volumes of information, it often turns out to be quite enough; in addition, USB 2.0 devices are fully compatible with newer USB ports. So nowadays you can still find pockets with this type of connection — these are basically the simplest and most inexpensive models.
— USB 3.2 gen1. Full size USB connector (not USB-C) compliant with version 3.2 gen1. This version (formerly known as USB 3.1 gen1 and USB 3.0) is the direct successor to USB 2.0, delivering up to 10x faster data transfer rates—up to 4.8Gbps—and more power. The mentioned speed is almost one-on-one with the capabilities of the popular SATA 3 internal interface; therefore, pockets with this type of connection are extremely common nowadays.
— USB-C 3.2 gen1. Connecting to a USB-C connector that complies with version 3.2 gen1. In terms of capabilities, this method is identical to the “normal” USB 3.2 gen1 described above, the difference lies only in the type of connector. USB-C is a relatively new standard used in both fixed and portable electronics. This connector is noticeably smaller than the standard USB A (slightly larger than microUSB), while it has a convenient double-sided design. However, specifically in computers and even laptops, USB-C ports are used much less frequently than full-sized USBs, so this option is relatively rare in pockets.
— USB C 3.2 gen2. Connecting to a USB-C connector that complies with version 3.2 gen2. See above for more details on USB-C in general. And USB 3.2 gen2 (formerly known as 3.1 gen2 or simply 3.1) is the successor to 3.2 gen1, with even more advanced features: the maximum connection speed in this standard is 10 Gbps. On the other hand, for SATA drives, such speed is unnecessary, support for this version is quite expensive, and USB-C 3.2 gen2 connection ports are still relatively rare. Therefore, this option has not received distribution in pockets either: it is provided only in individual models for M.2 SSD with PCI-E connection, where the speed of the internal interface is already measured in tens of gigabits per second.
— PCI-E. Connect to a standard PCI-E slot on the motherboard. In other words, such pockets are connected to the computer in the same way as video adapters, sound cards, and other expansion cards. This design is used in select internal models for M.2 SSD drives; using such a pocket, you can connect a similar drive to a desktop PC even if the native M.2 ports on the motherboard are busy, unavailable, not suitable for connection (for example, they use the SATA interface, while the drive is made for PCI-E), or absent altogether.
Note that such pockets are usually compatible with M.2 PCI-E SSD modules without problems, but compatibility with M.2 SATA should be specified separately (although such functionality is also found). It is also worth mentioning that PCI-E slots and devices for them can have a different number of lines, and the general rule here is this: the number of lines in a slot on the motherboard must be no less than that of the connected board. However, in pockets with such a connection, usually less than 4 lines are provided, so they can be connected to PCI-E connectors starting from 4x.
— IDE. Outdated interface for connecting internal drives. It is extremely rare in modern pockets — in separate models designed to install modern or HDD / SSD in outdated computers without SATA and other relevant connectors.
