Thunderbolt 线缆不支持 40GB/s，能不能是“TB3”

Question

据我了解，雷电 3 规格包括 40Gb/s 的比特率。如果只有 20Gb/s，那么这款 Startech 电缆怎么会是 TB3 呢？

https://www.startech.com/be/nl/Kabels/thunderbolt-3-kabels/thunderbolt-3-20gbps-usb-c-kabel~TBLT3MM2M

https://en.wikipedia.org/wiki/Thunderbolt_(接口)

Answer 1

这是无源 Thunderbolt 3 线缆，这意味着其速度限制为 20 GBit/s（非常短的线缆除外）。只有使用有源线缆才能实现 40 GBit/s 的最大速度。

有源电缆要贵得多。它们在内部与无源电缆不同，例如不能用于 USB 3.1 Gen1/2，只能用于 USB 2.0。它们也不直接支持 DisplayPort 信号（仅包含在 Thunderbolt 中）。

维基百科提供了更好的表格USB-C 文章：

+=============+=================================================================+=============================================================+==============+
|             |                               USB 3.1 Type-C cable              |                  Adapter cable or adapter                   |              |
|    Mode     | USB | DisplayPort | Thunderbolt           | superMHL | HDMI     | HDMI        | DVI-D                    | Component video    | Construction |
|             | 3.1 | 1.2   | 1.4 | 20 Gbit/s | 40 Gbit/s |          | 1.4b     | 1.4b | 2.0b | single-link | dual-link  | (YPbPr, VGA/DVI-A) |              |
+=============+=====+=======+=====+===========+===========+==========+==========+======+======+=============+============+====================+==============+
| DisplayPort | Yes | Yes         |                                             | No                                                          | Passive      |
|             +-----+-------------+                                             +-------------+--------------------------+--------------------+--------------+
|             |     | Optional    |                                             | Yes         | Yes                      | Yes                |       Active |
+-------------+-----+-------------+-----------+-----------+---------------------+-------------+--------------------------+--------------------+--------------+
| Thunderbolt | Yes | Yes         | Yes       | Yes [d]   |                     | No                                                          | Passive      |
|             +-----+-------------+-----------+-----------+                     +-------------+--------------------------+--------------------+--------------+
|             |     | Optional    | Optional  | Yes       |                     | Yes         | Yes                      | Yes                |       Active |
+-------------+-----+-------------+-----------+-----------+----------+----------+------+------+-------------+------------+--------------------+--------------+
| MHL         | Yes |                                     | Yes      |          | Yes  | No   | Yes         | No         | No                 | Passive      |
|             +-----+                                     +----------+          +------+------+-------------+------------+--------------------+--------------+
|             |     |                                     | Optional |          |      | Yes  |                          | Yes                |       Active |
+-------------+-----+-------------------------------------+----------+----------+------+------+-------------+------------+--------------------+--------------+
| HDMI        |                                                      | Yes      | Yes  | No   | Yes         | No         | No                 | Passive      |
|             |                                                      +----------+------+------+-------------+------------+--------------------+--------------+
|             |                                                      | Optional |                                        | Yes                |       Active |
+-------------+------------------------------------------------------+----------+----------------------------------------+--------------------+--------------+

...其中注释 d 为：“由于当前电缆技术的限制，Thunderbolt 3 40 Gbit/s 无源电缆只能达到 <0.5 米。”