Shulou(Shulou.com)11/24 Report--

When you start writing: ET believes that a real camera player should not only understand cameras, but also know something about computers, storage, and the Internet. After the official writing: ET hopes that you can have some understanding of computers, storage, and the network-- er... ET really wants to make the article shorter and more concise. But this piece of knowledge is really that complicated. For ease of understanding, the following has made some compromises in terms of scope and rigor.

▲ this is Intel's promotional map of the lightning interface, which means that the lightning interface can do the work of all other USB interfaces-- what's the problem in this picture later? Special thanks to teacher @ Fei Wei for the supplement and revision of this article.

Why did you insert a background here to write this article: we talked about this topic because you asked Xiaomi whether the 1TB high-speed mobile hard drive being crowdfunded is worth buying, and whether the Apple laptop he is using supports the 2000MB/s transmission speed of this hard drive. The conclusion is that Xiaomi's mobile solid state drive is cheap and competitively priced in products with both 1TB capacity and 2000MB/s transmission speed; but most computers can't achieve 2000MB/s transmission speed, and the situation on Apple laptops may be even worse.

* for reference: the price of the Kingston XS2000 is about $829, the SanDisk E81 is about $1099, and the Rexa SL660 is about $1299.

USB interface and speed pull back to continue to talk about USB and lightning interface. There are three main USB interfaces we use now:

USB Type An or USB-A for short: the most common USB interface on a computer, which supports maximum 10Gbps transmission speed

USB Type C or USB-C for short: a more and more widely used USB interface, which supports both positive and negative plug, and supports maximum 40Gbps transmission speed

USB micro-B or micro USB: interface for early Android phones, smart devices, and low-power charging devices that supports maximum 480Mbps transmission speeds (i.e. USB 2.0).

It is important to note that micro USB also has a version that supports USB 3.0, called USB 3.0 Micro-B or Micro-B SuperSpeed, which is mainly used for mobile hard drives and some medium and high-end digital SLRs (such as Canon 5D4, Nikon D850, etc.). The device slot consists of two-part contacts that can be transmitted only when plugged into an ordinary micro USB cable, but at a speed of only USB 2.0.

There is no time to actually shoot the ▲, so use the product map of Green Alliance, with USB-An on the top left, USB-C on the top right, micro USB on the bottom left, and micro USB supporting USB 3.0 on the lower right. The maximum bandwidth and actual transmission speed of several interfaces are also listed here. When it comes to 40Gbps, due to the relationship between bandwidth division and the main control chip, the actual transmission speed can not double that of 2GB / s. In order to break through this speed bottleneck, we can only look forward to the new interface technology standards and main control chips.

For the question in "Why did you write this article": the 2000MB/s transmission speed of Xiaomi mobile solid state disk is based on USB 3.2 Gen 2x2 interface. At present, only a few high-end machines and computer motherboards are equipped with this interface. The good news is that desktops with extra PCIe slots can buy an expansion card for less than 200 yuan to get this interface. The bad news is that laptop and Apple users don't have access to this interface at all (at least ET hasn't seen a docking station or converter that provides USB 3.2 Gen 2x2).

Connect the removable solid state drive with the USB 3.2 Gen 2x2 interface to the slower USB interface. It works, but it can't get up fast. (similarly, there are some high-end CFe B card readers)

A friend of USB4 and Lightning may ask, "the USB4 interface has been accelerated to 40Gbps, so what if I use 20Gbps's USB 3.2 Gen 2x2 device on the USB4 interface?" Well, the USB interface is indeed backward compatible, but USB4 is backward compatible with USB 10Gbps, so it skips USB 3.2 Gen 2x2-if you use USB 3.2 Gen 2x2 devices on USB4 devices, the top speed is only 10Gbps.

USB speed from the initial 1.0,1.1,2.0 to 3.0,3.1,3.2, followed a path of technological upgrading. After arriving at 10Gbps, there are branches: on one side is the self-contained USB 3.2 Gen 2x2, and on the other side is the USB4 interface borrowed from Lightning 3. As a result, the cost of USB 3.2 Gen 2x2 is not high, but there are not many hosts and devices supported over the years, while the USB4 interface looks more promising because it takes the express train of Lightning 3 and does not have the cost of compulsory certification of lightning equipment (at least AMD has invested a lot of resources).

Here we will talk about the relationship between Lightning 3, Lightning 4 and USB4:

Lightning 3 is the technical standard released by Intel and Apple in 2016. It uses the USB-C physical interface and another set of transmission protocols, provides the highest 40Gbps bandwidth, and supports the first-line transmission of data, charging and video. Key points: lightning 3 must use USB-C interface, but not all USB-C interfaces support lightning technology.

After that, USB 4.0 (2019) and Lightning 4 (2020) are actually based on Lightning 3, compatible with Lightning 3. It can be roughly understood that USB 4.0 is a popular version of Lightning 3, which cancels some compulsory certification (thus reducing costs), while Lightning 4 is a perfect version of Lightning 3, which optimizes the bandwidth allocation mechanism, improves the expansion ability of peripherals, and changes some features from "support, but not necessary" to "must".

I know this can be confusing, but I had to add the USB3 / DP option to the table below (the original Intel form is also designed this way), which represents a USB3 interface that supports video output-this is called a data / video interface, or "full-featured USB-C" interface on some laptops. It uses USB-C interface with USB4, Lightning 3 and Lightning 4, but the highest transmission speed and power supply capacity are not used at all.

If you only focus on transmission speed, then the theoretical bandwidth of Lightning 3, USB4 and Lightning 4 is 40Gbps. Lightning 3 has a transmission speed limit (22Gbps or 2.75GB / s) because of the data bandwidth allocation problem, while USB4 and Lightning 4 do not increase this speed too much (about 3.1GB / s) because of the main control chip. When Lightning 3, USB4, and Lightning 4 encounter other USB interface devices (including USB 3.2 Gen 2x2), the transmission speed is only the highest 10Gbps.

Finally, make up for it: according to some previous tests, the lightning interface of Apple M1 series chip computers does not support USB 10Gbps very well, only Mac Studio can run to 10Gbps, but there will still be some gaps with Intel models (after all, Intel has integrated lightning controllers into processors in recent years).

This article comes from the official account of Wechat: camera Notes (ID:xjbiji), by Teng Fei et

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