What is the difference between USB 3.0, 3.1, 3.2 and USB4?
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Family tree
We will probably skip the very ancient USB 1.1 standard (12 Mbit/s or 1.5 Mbps), which sank into oblivion in the mid-2000s, but we will talk in more detail about subsequent versions, which are more or less relevant to this day.
USB 2.0 is the oldest currently widely used wired data transfer interface. It was announced back in 2000, but it began to be popularized massively only since 2005. The theoretical speed is 480 Mbit/s (60 Mbps), but the practical speed is twice as low — about 30 Mbps. The main advantage is guaranteed support by all popular operating systems (including the old Windows XP) without the need to install drivers. Whereas USB 3.0 and newer ports can either work in slow motion or not work at all before installing drivers on the chipset.
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USB 3.0 (3.1 Gen 1, 3.2 Gen 1) — the first and twice renamed technology of high-speed wired data transmission for the sake of unification of names. The theoretical speed is 5 Gbit/s (625 Mbps), the real speed is about 450 Mbps.
USB 3.1 Gen 2 (3.2 Gen 2) — the second and fastest implementation of Universal Serial Bus that actually exists at the time of writing, with a theoretical speed of 10 Gbit/s (1250 Mbps) and a practical speed of about 900 Mbps.
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USB 3.2 Gen 2x2 — as you might guess from the name, once again doubled in speed technology. Theoretically, 20 Gbit/s (2500 MB /s) is stated, and how much will be in fact remains to be seen (probably somewhere 1800 Mbps). The final USB 3.2 specifications have already been approved, but there are no real devices yet. The first models are likely to be shown at the next Computex Taipei 2019 exhibition.
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USB4 is the upcoming standard that should unite USB 3.2 and Thunderbolt 3. The peak theoretical speed will be 40 Gbit/s (5000 Mbps). It will remain backward compatible with all previous versions, including USB 2.0.
We will tell you more about USB drives and their speeds using the example of a brand-new WD My Passport SSD with a volume of 1 TB.
Previously, the WD My Passport line of external USB drives consisted exclusively of hard drives. But the gradual reduction in prices for flash memory made it possible to create within this series the first portable solid-state — My Passport SSD, the volume of which varies from 256 GB to 2 TB. At the same time, it is about half the size and three times lighter than a typical 2.5-inch form factor hard drive.
Connects to a desktop PC, laptop, smartphone or tablet My Passport SSD via a high-speed two-way USB Type C 3.1 Gen 2 cable. In addition, the kit includes an adapter for a full-size USB Type A. The manufacturer claims a sequential read and write speed of up to 540 Mbps, which is three times faster than any external HDD. It is important to note that the speed indicators may differ depending on the volume of the drive.
In addition, My Passport SSD can withstand a fall from a two—meter height without loss of information, whereas even the most protected portable hard drives, clad in a thick layer of rubber, are able to survive a fall only from a height of 1.2 m. But there is no dust and water protection — this is the privilege of drives under the SanDisk brand, which now belongs to WD.
In addition to shock protection, 256-bit hardware AES encryption is provided. You can configure it, as well as backup, using the proprietary WD Discovery suite of applications. In general, My Passport SSD is a stylish—looking (maybe a little brand-new), lightweight and compact external solid-state drive, which is significantly faster and more secure than classic hard drives.
Test results
To test My Passport SSD, we used the following applications: Crystal Disk Info to display detailed technical characteristics of the drive, Crystal Disk Mark to measure the speed of sequential (linear) reading and writing in megabytes per second, Anvil's Storage Utilities to measure the speed of random reading and writing in IOPS (number of I/O operations per second) and file access time in milliseconds, as well as AIDA64 Disk Benchmark to check the reduction in the write speed of large files.
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According to the test results, the sequential read and write speeds in Crystal Disk Mark were 430 and 440 Mbps, respectively. For external USB drives, whether SSD or HDD, it is quite typical that writing is slightly faster than reading. The AIDA64 retest showed a decrease in speed after writing 100 GB of files from the original 440 to about 300 Mbps. This happens due to the overflow of the virtual SLC cache, the volume of which is equal to 10 percent of the volume of the disk (a feature of all SSDs with TLC flash memory).
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But the Anvil's Storage Utilities application traditionally underestimated the sequential read and write speeds compared to CDM (another testing technique), but intended a high speed of random reading and writing (36 and 40K IOPS) and vice versa low file access time (only 0.4 ms). Simply put, SSD operates with numerous small files without any noticeable delays. Namely, this parameter has always been a weak point of the HDD.
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The exFAT file system selected by default by WD for the My Passport SSD drive not only handles better with file fragmentation than FAT32, but also consumes the resource of overwriting flash memory cells more economically than NTFS. In addition, exFAT is compatible with all modern operating systems: Windows, macOS, Linux and Android (in the case of the latter two, you may need to install the appropriate driver). Whereas, if you want to use My Passport SSD for automatic backup using Apple Time Machine technology, you will have to resort to reformatting in APFS.
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Conclusions
USB 3.1 Gen 1 interface bandwidth is more than enough for flash drives and portable hard drives, and USB 3.1 Gen 2 is more or less enough for SSD. In turn, an even faster USB4 bus will be used primarily for external video cards, which are required not only for games, but also for professional photo processing, video editing and 3D modeling. This is especially true for laptops, in the thin case of which it is difficult to fit a truly powerful GPU. The first models of external video cards with the Thunderbolt 3 interface are already available for sale, but they are still expensive and do not work well enough. But I want to believe that with the beginning of the widespread introduction of USB4, external video cameras will become a truly mass product.
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