没有一个头脑正常的人会认为USB的出现是一件坏事。在我们第一次获得现在标志性的USB端口之前，世界充满了笨重、不同的连接标准。
90 年代初期的典型 PC 具有LPT、串行(Serial)、PS2、SCSI和MIDI端口。这仅仅是列举的一小部分！现在我们有了通用串行总线(Universal Serial Bus)，但它并不像人们希望的那样“通用”！
USB 版本和速度(USB Versions & Speeds)
重要的是要了解，虽然两个USB端口和电缆可能看起来(look )相同，但这并不意味着它们具有相同的功能。那是因为多年来USB标准有所改进。(USB)发送和接收信息的硬件速度更快，内部布线也有很大不同。
然而， USB(USB)的一个关键部分是“通用”位。实际上，这意味着如果USB电缆适合端口，它将起作用。可能发生的最坏情况是它默认为两个设备都能理解的最古老、最慢的标准。这(Which)意味着某些设备根本无法正常工作，因为它们无法足够快地通过电缆推送数据。
当您购买USB外围设备时，它会指定它支持和（有时）要求的最高标准。这意味着计算机、电缆和设备都必须符合特定的USB标准才能尽可能地运行。
目前已经有三代USB出现在野外，第四代尚未发布，但正在开发中。这是您至少需要知道的：
- USB 1的最大理论速度为 12Mbps（兆位每秒）。这些旧设备可以与当前的现代USB一起使用，但速度不会超过那个速度，而且通常速度会更低。它也被称为“全速” USB，这可能会造成混淆。
- USB 2速度更快，(way )最大理论速度为 480Mbps。USB 2的营销名称是“高速”。
- USB 3是撰写本文时的最新标准，理论速度达到惊人的 5 Gbps（千兆位/秒）。它的营销名称是“SuperSpeed”。
USB 1.1实际上是最广泛采用的USB 1标准，几乎没有USB 1.0设备进入用户手中。USB 2.0 只接受了一次修订，但USB 3与(USB 3)USB 3.1和 3.2 的修订工作最多。
这些又(further )分为几代。USB 3.1有Gen 1和Gen 2细分。USB 3.2具有Gen 1 ,2 和 2×2。
代际版本实际上在性能上有显着差异。USB 3.1 Gen 1以 5 Gbps的速度运行，但Gen 2的速度翻了一番！USB 3.2代分别以 5,10 和 20 Gbps的速度运行。
呸！
关于 USB-C 上的 Thunderbolt 3 的说明(A Note On Thunderbolt 3 Over USB-C)
Thunderbolt 3是一个完全独立于USB的数据传输标准。但是，它使用相同的USB-C端口！这并不像听起来那么令人困惑，所以让我们分解一下您需要知道的内容：
- 任何 USB-C 设备都可以在任何Thunderbolt 3端口上工作。
- 如果没有Thunderbolt ， Thunderbolt设备将无法在普通 USB-C 端口中工作。
- Thunderbolt USB-C端口旁边通常有一个小的闪电图形。
- USB-C 电缆可用作Thunderbolt电缆，但便宜的电缆可能无法正常维持速度。
- Thunderbolt电缆也可用作 USB-C 电缆。
Thunderbolt是一种简洁的技术，但本文是关于USB的，所以我们将把它留在那里。
USB 端口类型(USB Port Types)
现在我们已经介绍了不同的USB代，让我们来谈谈实际的物理端口。然而，在我们这样做之前，这里有一个快速提示——USB 3端口内部通常是蓝色的！这使得将它们与旧的USB(USB)端口类型区分开来很容易。
原来的USB端口被称为A 型(Type A)端口。这是我们都知道和喜爱的端口类型，可以在从平板电视(TVs)到时钟收音机的所有设备上找到。USB 1 和USB 2 Type-A端口内部只有四个引脚。两个用于数据，两个用于电源。USB 3 Type-A端口共有九个引脚，但完全向后兼容。
接下来是不太常见的 B 型(Type B)端口。这些通常出现在打印机或外部硬盘驱动器等设备上。对于不是“主机设备”（如计算机）的设备，它是一个母端口。B型USB 1(B USB 1)和 2 端口在物理上与USB 3 B 型端口(Type-B)不(not )兼容。
最后，我们拥有最新的 Type-C 端口。这个微小的、密集接线的端口是可逆的。这意味着与A 型(Types A)或 B 型端口不同，您可以以任何方式插入它。使用适配器，这与除USB 1之外的所有(USB 1)USB兼容。从USB 3.2(USB 3.2)开始，它取代了其他连接类型。
这就是所谓的“标准”端口，但对于那些太小而无法处理全尺寸 USB-A 端口的设备，还有“迷你”和“微型”版本。游戏(Game)控制器、智能手机和其他小型设备可以配备Mini和Micro版本的Type-A和Type-B端口。也有用于既作为主机又作为外设的设备的 Type-AB端口。(Type-AB)
在USB-C端口之前，智能手机最常配备Micro-B端口。Mini-B 端口可以在PlayStation 3控制器等设备上找到。
虽然Micro-B端口仍广泛用于智能手机、移动电源和大多数现代小型电子设备，但USB-C正迅速成为所有(every )使用USB的设备的新标准，无论大小。
USB 电源标准(USB Power Standards)
USB不仅仅是在设备之间传输数据的一种方式。这也是一种传递权力的方式。除了 Apple 的移动设备外，几乎所有现代智能手机都使用一种或另 一种USB端口进行充电和数据传输。(USB)
事实上，许多根本不传输数据的设备仍然使用USB进行充电。一个例子是小型玩具无人机的移动电源。一些USB电缆只带电，缺少数据传输的布线。移动电源随附的 电源线有时属于这种类型。(Power)
使用仅供电电缆来防止移动设备感染病毒实际上非常有用。例如，在可能提供充电器的机场，黑客(hackers)可以将它们换成受恶意软件感染的设备。所谓的“数据拦截(data blocker)器” USB电缆可防止该特定漏洞。
就通过USB电缆提供的实际功率而言，存在很大差异。但是，您应该知道的一件事是，如果您将USB设备插入USB兼容端口，它只会消耗所需的电量或端口可以提供的电量，以最低者为准。
因此，您不必担心将手机插入额定功率比随附的充电器更高的充电器。只要设备和电缆都来自信誉良好的制造商，就不需要考虑。
重要的是要知道一些USB电源不能很好地为您的设备充电或供电。USB根据硬件的代数提供电源。USB 1.0 和 2.0 提供 500mAh 的电流。USB 3.0 可提供高达 900 mAh 的电量。USB 3.1 可提供高达 3000 mAh (3A) 的电量！
这些只是制造商必须遵守的数字，以满足最低认证要求。您可能已经注意到，车载充电器和Apple iPad 充电器的额定电流通常为 2.1A，这不是任何USB规范的一部分。为了利用额外的可用功率，设备需要与充电器对话以协商它需要多少功率。
如果不能，它将简单地默认为最小值，通常为 500 mAh。您需要知道的是，充电器和设备都必须支持相同的“快速充电”电源标准，该标准将在USB规格之上传输。
除了最新 USB 3 版本的高功率输出外，所有其他快速充电标准都不是行业标准。因此，无法保证您的“快速充电”智能手机会在第三方充电器上以最佳速率启动。
例如，在Android手机上，通常会有一条通知让您知道设备充电速度是慢还是快，以及时间估计。
在 Mac 上使用 USB(Using USB On Macs)
(USB)自从USB(USB)本身存在以来， USB就一直是Apple计算机的一项功能。1998 年的第一台 iMac 取消了除两个USB端口和两个FireWire端口之外的所有(FireWire)端口(Ports)。毫不夸张地说，Apple在(Apple)USB采用方面发挥了重要作用。
现代 Mac在(Modern Macs)USB技术方面也做了一些激进的事情，并取消了所有(ALL)端口以换取一个或两个USB-C端口。这意味着，如果您想使用任何本身不使用USB-C的设备，唯一的解决方案就是USB-C集线器。
好消息是USB-C具有如此多的带宽和功率，添加一个便宜的集线器设备可以为您提供任何您想要的连接。一定要寻找一款经过专门测试的Mac兼容性。带有两个USB-C端口的(USB-C)Mac Books可以与所谓的“双集线器”设备配合使用，这些设备可以插入两个USB-C端口并将它们结合起来与集线器一起使用。
关于 USB 4 的最后说明(A Final Note On USB 4)
在我们合上关于USB的书之前，我们需要简单谈谈未来。USB 4即将到来，因此最好为此做好准备。这一新标准支持高达 40 Gbps的带宽，但仅向后兼容USB 3.2和USB 2.0。
实际上，这不太可能打扰任何人，因为所有USB 1硬件基本上都已经过时了。当前的USB -C 端口将成为USB 4的中流砥柱，因此所有USB都在统一，不再担心不同端口是否可以协同工作。因此，在短短几年内，您将不必记住您在本文中读到的任何内容。
USB Cable Types Explained – Versions, Ports, Speeds, and Power
Nо one in their right mind could argue that the advent of USB waѕ a bad thing. Before we first got the now-iconic USB port, the world wаs filled with clunky, disparate connection standards.
The typical PC from the early 90s sported LPT, Serial, PS2, SCSI and MIDI ports. To name but a few! Now we have the Universal Serial Bus, but it’s not quite as “universal” as one might hope!
USB Versions & Speeds
It’s important to understand that although two USB ports and cables might look identical, it doesn’t mean they have the same capabilities. That’s because USB standards have improved over the years. The hardware that sends and receives information is faster and the internal wiring differs significantly.
Yet, a key part of USB is the “universal” bit. In practice this means that if a USB cable fits into a port, it will work. The worst that can happen is that it defaults to the oldest, slowest standard that both devices can understand. Which means that some devices simply won’t work properly because they can’t push data through the cable quickly enough.
When you buy a USB peripheral, it will specify which the highest standard is that it supports and – sometimes – requires. That means the computer, the cable and the device must all comply with that particular USB standard for it to run as well as possible.
Right now there are three generations of USB out in the wild, with a fourth as yet unreleased, but in the works. This is the least you need to know:
- USB 1 has a maximum theoretical speed of 12Mbps (megabits per second). These old devices will work with current modern USB, but at no more than that speed and usually a lower one. It’s also referred to as “Full Speed” USB, which can be confusing.
- USB 2 is way faster, with a maximum theoretical speed of 480Mbps. The marketing name for USB 2 is “High Speed”.
- USB 3 is the most recent standard at the time of writing and has a theoretical speed of an astonishing 5 Gbps (gigabits per second). Its marketing name is “SuperSpeed”.
USB 1.1 is actually the most widely-adopted USB 1 standard, with virtually no USB 1.0 devices making it into the hands of users. USB 2.0 received a single revision, but USB 3 has had the most revision work with USB 3.1 and 3.2.
These are further divided into generations. USB 3.1 has a Gen 1 and Gen 2 subdivision. USB 3.2 has Gen 1,2 and 2×2.
The generational versions are actually significantly different in performance. USB 3.1 Gen 1 runs at 5 Gbps, but Gen 2 doubles that! The USB 3.2 generations run at 5,10 and 20 Gbps respectively.
Phew!
A Note On Thunderbolt 3 Over USB-C
Thunderbolt 3 is an entirely separate data transmission standard to USB. However, it uses the same USB-C port! This isn’t as confusing as it sounds, so let’s break down what you need to know:
- Any USB-C device will work in any Thunderbolt 3 port.
- A Thunderbolt device will not work in a plain USB-C port without Thunderbolt.
- Thunderbolt USB-C ports often have a small lightning bolt graphic next to them.
- USB-C cables work as Thunderbolt cables, but cheap ones might not sustain the speed properly.
- Thunderbolt cables work as USB-C cables too.
Thunderbolt is a neat technology, but this article is about USB, so we’ll leave it at that.
USB Port Types
Now that we’ve covered the different USB generations, let’s talk about the actual physical ports. Before we do that however, here’s a quick tip – USB 3 ports are conventionally blue inside! That makes it easy to tell them apart from older USB port types.
The original USB port is known as the Type A port. This is the port type we all know and love, which can be found on everything from flat-panel TVs to clock radios. USB 1 and USB 2 Type-A ports have just four pins internally. Two for data and two for power. USB 3 Type-A ports have nine pins in total, but are completely backwards-compatible.
Next we have the less common Type B port. These are usually seen on devices like printers or external hard drives. It’s a female port for devices that aren’t “host devices” like a computer is. Type B USB 1 and 2 ports are not physically compatible with USB 3 Type-B ports.
Lastly, we have the latest Type-C port. This tiny, densely-wired port is reversible. Which means that unlike Types A or B ports, you can insert it any way around. With an adapter, this is compatible with all USB except for USB 1. It replaces other connection types as of USB 3.2 onwards.
That’s it for the so-called “standard” ports, but there are “mini” and “micro” version of these for devices that are too small to handle full-sized USB-A ports. Game controllers, smartphones and other small devices can feature Mini- and Micro- versions of Type-A and Type-B ports. There are also Type-AB ports for devices that act as both a host and a peripheral.
Before USB-C ports, smartphones most commonly featured Micro-B ports. Mini-B ports can be found on devices like the PlayStation 3 controller.
While Micro-B ports are still widely in use for smartphones, power banks and most modern small electronics devices, USB-C is quickly becoming the new standard for every device that uses USB, regardless of size.
USB Power Standards
USB is more than just a way to transfer data between devices. It’s also a way to transfer power. With the exception of Apple’s mobile devices, just about every modern smartphone uses a USB port of one type or another for both charging and data.
In fact, plenty of devices that transfer no data at all still use USB for charging. One example is power banks to small toy drones. Some USB cables only carry power, lacking the wiring for data transmission. Power cables that comes with power banks are sometimes of this type.
It’s actually pretty useful to use a power-only cable to prevent virus infections of mobile devices. For example, at airports where chargers may be provided, hackers can swap them out with malware-infected devices. A so-called “data blocker” USB cable prevents that particular exploit.
In terms of the actual power that comes through a USB cable, there’s a lot of variability. However, one thing you should know is that it if you plug a USB device into a USB-compliant port, it will only draw as much power as it needs or as much power as the port can supply, whichever is lowest.
So you don’t have to worry about plugging your phone into a charger with a higher power rating than the one it came with. As long as both devices and the cable are from reputable manufacturers, it’s not something you need to think about.
What is important to know is that some USB power sources aren’t going to charge or power your device well. USB provides power according to the generation of the hardware. USB 1.0 and 2.0 provide 500mAh of current. USB 3.0 can give up to 900 mAh of juice. USB 3.1 can provide as much as 3000 mAh (3A)!
These are simply the numbers a manufacturer must comply with in order to meet the certification minimums. You’ve probably noticed that car chargers and Apple iPad chargers are often rated for 2.1A, which is not part of any USB specification. In order to make use of the extra power available, the device needs to talk to the charger to negotiate how much power it wants.
If it can’t, it will simply default to the minimum, which is usually 500 mAh. All you need to know is that the charger and device both have to support the same “quick charging” standard of power that’s to be transferred above the USB specifications.
Apart from the high power delivery of the latest USB 3 versions, all other quick charging standards are not industry-standard. So there is no guarantee that your “fast-charging” smartphone will power up at its best rate on a third-party charger.
On Android phones, for example, there will usually be a notification letting you know if the device is charging slowly or quickly, along with a time estimate.
Using USB On Macs
USB has been a feature of Apple computers for almost as long as USB itself has existed. The first 1998 iMac did away with all but two USB ports and two FireWire Ports. It’s no great exaggeration to say that Apple had a big role to play in USB adoption.
Modern Macs have also done something radical when it comes to USB technology and have done away with ALL ports in exchange for one or two USB-C ports. This means that if you want to use any device that doesn’t natively use USB-C, the only solution is a USB-C hub.
The good news is that USB-C has so much bandwidth and power, that adding an inexpensive hub device can give you any connection you’d like. Be sure to look for one that has specifically been tested for Mac compatibility. MacBooks with two USB-C ports can work with so-called “dual-hub” devices, which slot into both USB-C ports and combines them for use with the hub.
A Final Note On USB 4
Before we close the book on USB, we need to talk briefly about the future. USB 4 is on the horizon and so it’s a good idea to be somewhat prepared for it. This new standard supports up to 40 Gbps of bandwidth, but is only backwards-compatible with USB 3.2 and USB 2.0.
In practice this is unlikely to bother anyone, since all USB 1 hardware is already essentially obsolete. The Current USB-C port will be the mainstay of USB 4 and so all USB is being unified, making worries about whether different ports will work together a thing of the past. So in just a few years, you won’t have to remember anything you read in this article.
