USB — Knowing the Basics of Universal Serial Bus

Universal Serial Bus (USB) is an industry standard that establishes specifications for cables and connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad variety of USB hardware exists, including eleven different connectors, of which USB-C is the most recent.

Figure 1.  Lenovo T495

Figure 2.  Lenovo ports layout

Always On USB 3.1 connector (Figure 2.9)

• There is a feature called "Always On USB" which allows devices connected to the laptop via USB to be powered over USB even when the Operating system (Windows 10 in my case) shuts down.

USB 2 and USB 3 Compatibility

• USB 3.0 backwards is compatible—meaning it's designed to work with older USB versions including USB 2.0 and USB 1.1. 
• You can plug a USB 2.0 device into a USB 3.0 port and it will always work, but it will only run at the speed of the USB 2.0 technology.
• USB 3.0 Flash Drives and card readers are backwards compatible with USB 2.0 and USB 1.1 ports. The USB 3.0 Flash Drive or card reader will work at the speed of the port, for example if you use a USB 3.0 Flash Drive in your USB 2.0 laptop, it will work at USB 2.0 speed.

USB Type C vs USB 3.1 Gen 2

• The USB Type C standard defines only the physical connector while the USB 3.1 Gen 2 standard applies only to the electrical signal. 
• USB 3.1 connector Gen 2 (Figure 2.18)
• Also referred to as SuperSpeed+
• USB-C connectors (USB 3.1 Gen2; Figure 2.20)
• USB-C is an industry-standard connector for transmitting both data and power on a single cable.
• The physical USB-C connector isn’t backwards compatible, but the underlying USB standard (could be USB 2.0 or 3.0) is.
• But that doesn’t mean you have to discard all your old peripherals. USB 3.1 is still backwards-compatible with older versions of USB, so you just need a physical adapter with a USB-C connector on one end and a larger, older-style USB port on the other end. 
• The USB-C connector looks similar to a micro USB connector at first glance, though it's more oval in shape and slightly thicker to accommodate its best feature: flippability. Like Lightning and MagSafe, the USB-C connector has no up or down orientation.
• Even if you get a computer with only USB Type-C ports, like Apple’s new MacBook, adapters and hubs will fill the gap.

Figure 3. USB Standards^[1]

USB Connectors

Sizes

• default—standard format intended for desktop or portable equipment
• mini—intended for mobile equipment
• micro—intended for low-profile mobile equipment such as mobile phones and tablets

Speeds (Figure 3)

• USB 2.0—Low, Full, High Speed
• USB 3.1 Gen 1—SuperSpeed (or SS in Figure 3)
• USB 3.1 Gen 2—SuperSpeed+ (or SS+ in Figure 3)

Shape (Figure 4)

• Type-A
• Type-B
• Micro-B
• Type-C

Figure 5.  USB Shapes

Figure 6. USB Plug Types (SS: SuperSpeed)

Figure 7. USB port symbols

References

1. USB Type C and USB 3.1 Gen 2 – Clarifying the Connection
2. USB Hardware (Wikipedia)
3. What Is USB-C? An Explainer
4. USB Implementers Forum (USB-IF)
5. Levnovo USB-C Laptop Power Bank 14000 mAh
• Power delivery (PD) is lower than 65w
6. The Best USB and USB-C Hubs
7. USB Type-C Explained: What is USB-C and Why You’ll Want it
• The USB PD specification supported by USB-C ups this power delivery to 100 watts. 
• It’s bi-directional, so a device can either send or receive power. And this power can be transferred at the same time the device is transmitting data across the connection. 
• This kind of power delivery could even let you charge a laptop, which usually requires up to about 60 watts.
8. USB Power Delivery 2.0 vs 3.0
• USB PD 3.0 ensures backwards compatibility with USB PD 2.0. All USB PD 3.0 sources and sinks are required to fully interoperate with USB PD 2.0 sources and sinks. This requirement is enforced by requiring all USB PD 3.0 devices to pass USB PD 2.0 compliance tests. In fact, from the USB Implementers Forum (IF) point of view, there are only USB PD products. The USB-IF does not distinguish between USB PD 2.0 products and USB PD 3.0 products when issuing USB logo certification.
9. Lenovo T495 Hardware Maintenance Manual
10. ThinkPad T495 Spec (pdf)
• Standard Ports
• 1x USB 3.1 Gen 1 (Always On)
• 1x USB 3.1 Gen 2
• 2x USB-C 3.1 Gen 2 (support data, PD and DP 1.4)
11. ThinkPad T495 User Guide (pdf)
• USB-C connectors (USB 3.1 Gen2)
• Charge your computer.
• Charge USB-C compatible devices with the output voltage and current of 5 V and 1.5 A.
• Transfer data at USB 3.1 speed, up to 10 Gbps.
• Connect to an external display:
• USB-C to VGA: 1900 x 1200 pixels, 60 Hz
• USB-C to DP: 3840 x 2160 pixels, 60 Hz
• Connect to USB-C accessories to help expand your computer functionality. To purchase USB-C accessories, go to https://www.lenovo.com/accessories.
• Supply power to another computer using P-to-P (Peer to Peer) 2.0 charging function. See “Use P-to-P 2.0 charging function” on page 25.