158

I'm currently planning the setup for a new computer. As I were browsing through computer cases I realized that most modern computer cases still have a mix of USB 2.0 and 3.0 ports on the front panel.

Is there a legitimate reason to still have or use USB 2.0 ports on modern PC cases? As far as I know USB 3.0 has backward compatibility

Example image of a random case showing USB 2.0 ports to the left and USB 3.0 ports to the right.

Example image of random case be quiet! Silent Base 600 source

  • 3
    Shouldn't you expand your question to include all mainline computers, mainboards, etc, and not only front panels? Some MBs still include PS/2 ports, for a very good reason. – Ale..chenski Aug 12 '16 at 23:14
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    I have always guessed size is the reason, 3.0 motherboard headers are huge compared to 2.0. – PGmath Aug 13 '16 at 4:26
  • 6
    @PGmath the header size is probably part of it. The fact that the way Intel does its chipsets means you almost always have some 'spare' 2.0 only headers available is another one. ex the X170 chipset has support for a maximum of 14 USB ports: 10 of which can be USB3, the remainder are limited to 2.0. However due to sharing of high speed IO lanes from the chipset (26 total, of which up to 10 can be USB3, 6 SATA, or 20 PCIe 3 - and m.2 SSDs need 2 or 4 lanes each) most mobos have fewer than that unless they use extra chips to add more. – Dan Neely Aug 13 '16 at 19:26
  • 3
    The case I bought a couple of months ago has only USB 3.0 ports on the front. Perhaps this was designed when USB 3.0 was very new. – Michael Hampton Aug 14 '16 at 6:25
  • 2
    @ChrisH - I believe that you're theoretically right, but I think I've seen USB 3.0 ports that were not blue. – Joe Aug 16 '16 at 4:46

20 Answers 20

143

Nobody has mentioned this yet, but USB 3.0 ports can cause issues with certain installation media (cough Windows 7 cough) where only USB 2.0 drivers are provided on the installation media.

Another key point mentioned by @togh is that USB 3.0 requires a large amount of bandwidth, which can congest existing PCI-E lanes if all of the USB 3.0 ports are in use. Using 2.0 (with it's lower bandwidth) allows more devices to be used (which may not necessarily need the high bandwidth USB 3.0 provides; e.g. most user input devices) while maintaining open PCI-E lanes for other peripherals.

  • 4
    Yeah, a USB 3 controller won't normally work with a USB 2 driver, and this is often peoples' first encounter with that limitation. More fully-featured motherboards will let you override the onboard ports to USB 2 mode (superuser.com/questions/480045/…), but on lower end boards this often isn't an option, and if you're lucky there's still an actual USB 2 port somewhere... – rakslice Aug 16 '16 at 22:56
  • 10
    Maybe we should tell Microsoft to bundle USB 3.0 drivers as well. – Calmarius Aug 17 '16 at 13:03
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    Installing Windows 7 on a USB 3 only Laptop without optical media has been one hell of a ride. – musiKk Aug 17 '16 at 13:08
  • 1
    Also some low-level software doesn't operate correctly with USB3 ports. Virtualbox's USB sharing facility, for example, only works with USB2. – Jules Aug 18 '16 at 2:23
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    The weird thing is, the Windows 7 installation is starting properly until you get stuck at the screen where you need to select the hard disk. The list is empty. It took me a lot time to found out I should use the USB 2.0 port instead of 3.0.. – com2ghz Aug 18 '16 at 9:20
87

USB 3.0 does have backwards compatibility, but if you, for some reason, happen to buy a motherboard that does not have a USB 3.0 header connection (only back I/O USB 3.0 ports), you're left without any front panel USB ports at all. That's one possible explanation.

  • 5
    There are adapters to connect USB3 to USB2 headers. That point is sorta moot. Also, these adapters cost around 3€. – Ismael Miguel Aug 12 '16 at 17:05
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    Erm. USB3.0 has backward compatibility in spec, but there are devices in the real world that are totally non-compliant and will function consistently on USB2.0 but for some reason consistently malfunction on 3.0. – ζ-- Aug 12 '16 at 20:27
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    my mobo has a 3.0 header but an oversize video card = theres no room to plug the cables in or to slip an adapter/angle changer thing in – Kevin L Aug 12 '16 at 20:47
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    With @hexafraction, I have an older usb wifi adapter I sometimes plug into my tower. My computer won't pick it up if it's plugged into a 3.0 port but it works just great in a 2.0 port. – Ryan Aug 13 '16 at 0:16
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    @IsmaelMiguel If you don't mind killing your motherboard, sure, use an adapter. There's no way the adapter can compensate for the load differences between USB2 and USB3 - that's the whole reason why USB3 has different connectors in the first place. While USB connectors have the same physical layout, they are quite different electrically. – Luaan Aug 15 '16 at 7:58
55

No, there is no reason - except cost.

There is no technical advantage from having a USB 2.0 port instead of a USB 3.0 port; but it is also not a big selling point to upgrade all ports instead of some only, so the extra effort of redesigning the hardware layout to have only USB 3.0 ports is often delayed or avoided.

As others pointed out, most people assign devices to the ports that would have no advantage of USB 3.0, so they don't care about the ‘limitation.’

If I'm designing a computer, I would not design any USB 2.0 in there; actually, there are many computers that do not have USB 2.0 anymore (mine doesn't). It just depends which ones you check.

My impression is that the market for towers is generally receding, and losing to laptops; little is done to their design therefore. Laptops are not more expensive anymore and much more practical.

  • Comments are not for extended discussion; this conversation has been moved to chat. – Mokubai Aug 15 '16 at 17:09
51

USB 2 ports are handy for keyboards and mouse controllers and other non-drive uses, because those device do not need the speedy throughput of USB 3. A keyboard or mouse connected on USB 3 would be a waste of the resource.

  • 9
    This is not a bad answer, but if all of the USB ports on the case pictured would be USB 3.0, the same logic would still apply. Just have 4 USB 3.0 ports instead of splitting the difference between USB 2.0 and USB 3.0. – JakeGould Aug 12 '16 at 18:15
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    This answer is the best one. There is no "but". USB3 requires two extra differential pairs, so it takes 3X more system resources: 3x number pf pins on SoC/processor, 3X more board space, 3x more internal cabling. Plus it requires much more electrical care for 10x signal speed. Plus 2X more connector pins. This is the wasted resource if you use a USB3 port for mice, keyboard, IR dongle, BT dongle, audio/headphone adapter, and all these Adruino/Raspberry stuff. All these devices will not be in USB3, I would say "never", because there is no economical reason. – Ale..chenski Aug 12 '16 at 20:03
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    @Ghainma: your reasoning is flawed. Use of USB2 interface for USB1.1 devices does not constitute waste of material resource for a system, since all LS/FS/HS devices operate over the same set of wires, while USB3 requires 3x more. BTW, not long time ago not every BIOS would have software means to support USB2 hardware, so only FS/LS devices would be available with system BIOS. Just like today not every BIOS/UEFI can properly support xHCI (USB3.0) controllers. – Ale..chenski Aug 12 '16 at 20:17
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    Why would you plug mouse and keyboard into a front panel USB? – gronostaj Aug 12 '16 at 21:19
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    @gronostaj: My mouse's wireless receiver is always on my front panel USB. Otherwise I have to dismantle my desk whenever I want to take my mouse somewhere.... seems pretty obvious. What else would front-panel ports be, aside from convenience and ease of access? – Lightness Races in Orbit Aug 14 '16 at 14:07
36

On newest motherboard, you often have USB2, USB3.0 and USB3.1

  • The required bandwidth for each is different:

    • USB 2.0 => 280 Mbit/s
    • USB 3.0 => 5 Gbit/s
    • USB 3.1 => 10 Gbit/s (for Gen 2)

    But in term of usage, we still have a lot of peripherals that still satisfies from the "slow" USB2. Most of the mouse and keyboards, still a lot of flash drives, some flash card readers etc.

    For the skylakes processors (latest at this date), the chipsets also have their limitations: http://www.tomshardware.com/news/intel-100-series-hsio-chipset,30210.html Source here.

    You can see that if all SATA/USB 3.0/ and GbE are used, the remaining number of PCI-E 3.0 lanes get quite low.

    You will also notice that no USB 3.1 are provided, they need to add a different chip for this functionality (probalby reducing the number of PCIe 3.0 lanes)

    There is a need for a compromise, it would be pointless to build a lot of usb 3.0 that can't all run at full specifications.

    Its better to make use of these cheep USB 2.0 that are available (14 on the high end and still 10 on the lower end) and consume nearly nothing, and increase the connectivity possibilities, than only the reduced number of USB 3 ports.

    Having the same number of USB 3.1 ports would probably need higher cost and impose them to share bandwidth. This means the only advantage would be that you don't have to look where you plug high speed devices.

  • In a comment, @Luaan also pointed out that power requirements are also increasing with the newer standards. The USB Power Delivery can go as high as 100W per USB, but few computer could provide 10 times this power.

  • And as @Patrick Bell and some other mentioned there can be some compatibility problem with the USB 3.0 and USB3.1, which makes safer to still have USB 2.0.

  • This is by far the most logical answer; especially mentioning USB 3.1. On most Skylane boards, there's simply a single 3.1-typeC port, most likely due to bandwidth limitations as stated. – djsumdog Aug 18 '16 at 20:46
  • I feel this answer is much more comprehensive and helpful than mine. Mind if I edit this into the bottom of my post at the top with due credits? – Patrick Bell Aug 19 '16 at 22:20
  • @PatrickBell So I would say a quick resume of the points you find interesting in my post and a link to it, so they can see it here. This way we have complementary posts instead of overlapping. – Togh Aug 20 '16 at 6:37
  • @Togh Sorry, I didn't explain very well. I just wanted to throw in an edit talking about some of your points. Edited my post! – Patrick Bell Aug 20 '16 at 18:45
17

I don't have any confirmed knowledge that this is the case, but I have always assumed that the reason they still include a couple 3.0 plugs is because USB 2.0 headers are so small compared to USB 3.0 it isn't much of a problem to just slap a couple on as extra.

For comparison, here is a picture of a 3.0 to 2.0 converter, note the size difference between the quite hefty USB 3.0 header (bottom) and the relatively tiny 2.0 header (top), which is actually two USB 2.0 headers side-by-side.
enter image description here
If you have ever built a computer with USB 3.0 plugs in the case the difference is quite obvious. Not only do 3.0 headers take up 3x-4x as much physical space, they also have to be a bit heavier and more robust. These size differences account not only for the headers themselves but for all the extra traces the USB 3.0 requires as well.

After all, as many others have mentioned, there are lots of things (mice, keyboards, etc.) that work fine on USB 2.0. The only things that really need the enhanced capability of USB 3.0 are storage devices, so it doesn't make much sense to take up all that space on the motherboard for more 3.0 connectors when there will probably be multiple devices that don't need them.

  • 2
    The USB 3.0 header on the pictured adapter is also a dual-port type. – user2943160 Aug 13 '16 at 16:55
  • @user2943160 Are you sure? All the single port ones in my computer look like that. – PGmath Aug 13 '16 at 17:12
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    Yes. Notice in the image how all 8 pins (2x of power, ground, D+, D-) of the USB 2.0 connector are used. Standard pinout in Section 2 of www-ssl.intel.com/content/dam/doc/technical-specification/… – user2943160 Aug 13 '16 at 17:16
13

USB 2.0 ports can allow backwards compatibility with some devices. At my job, we had to use the USB 2.0 ports with some network cards we had because their drivers didn't support USB 3.0, and the WiFi connection would cut in and out when we had the card plugged into a USB 3.0 port.

  • 5
    You can always use a USB2 extender (short version), which does not have USB3.0 wires. In this way you can "convert" any USB3 port into USB2 port, which should solve all your driver problems. – Ale..chenski Aug 12 '16 at 21:53
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    @AliChen "should" in a world where the ideal, fully compatible implementation is the one manufacturers actually provide. Other answers show that, in reality, this is sadly often not the case. – underscore_d Aug 15 '16 at 11:06
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Not all motherboards have USB 3.0 port headers. While USB 3.0 is backwards-compatible from the peripheral's point of view - you can plug a USB 2.0 device into a USB 3.0 port and have it work, and you can plug a USB 3.0 device into a USB 2.0 port and have it work as a USB 2.0 device - but you can't connect a USB 3.0 port on the case to a USB 2.0 header on the motherboard because the connectors are different.

  • @JakeGould I didn't want to say USB 2.0 specifically, because as far as I know there are other USB 2.x versions that aren't 2.0. – Micheal Johnson Aug 12 '16 at 19:39
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    There is only one USB 2.0 and USB 3.0; no other versions. The only version that had another integration within it’s major version was USB 1.1 which was a bug-fix for USB 1.0. There might be a USB 3.1 but nothing has come out for that specific spec yet. – JakeGould Aug 12 '16 at 23:07
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Certain system architectures only have USB 2 controllers built-in, so USB 3 support has to be added with an additional controller. But why waste the otherwise unused USB 2 controller ports? Since everyone has plenty of peripherals that don't need USB 3 (like keyboards) they often use some of the USB 2 controller ports to fill out the port count.

  • 1
    I'd note that most cases only have 2 USBs on the front panel, and most MBs only have one USB header (for two USB ports), so you're not losing anything by having a 2+2 combo instead of (the most common) 2x USB or (the mostly useless) 4x USB. For very little extra expenditure, you have a case that can support both old and new motherboards well. – Luaan Aug 15 '16 at 8:46
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I think there are a couple of reasons.

Firstly USB 3.0 ports and the associated wiring are more expensive than USB 2.0 ones and frankly most devices don't need USB 3.0 speeds.

Secondly (unless you integrate a hub in the case) you need a connector on the motherboard for each pair of USB ports. Most motherboards only have one connector for front USB 3.0.

It’s possible to use an adaptor to connect a pair of USB 3.0 front ports to a USB 2.0 motherboard header but doing so creates user confusion as the PC ends up with ports that look like USB 3.0 but are really only USB 2.0.

8

USB 2 uses less bandwidth.

Understand that bandwidth is not just some sort of magical number. There is actual science behind it. Computers are real, physical things. Electricity does travel down the pathways that are designed for such electrical travel. Implementing this feature does take up some sort of space. I imagine there may be other requirements, like making sure that data can get processed sufficiently fast.

So, the ability to support a higher speed may require more resources. That advantage of USB 2 ports is that there may be some cases where you can fit

  • two USB 2.0 ports,
    • but not two USB 3 SuperSpeed ports.
Or maybe even cases where
  • one USB 2.0 port can be supported,
    • instead of zero USB 3 SuperSpeed ports.

When USB 3 was first released, many systems did not support the new standard at all. Those that did would typically only support 1 or 2 of these "SuperSpeed" ports. Eventually, technology is expected to improve and USB 3 ports will likely be considered less phenomenal. People will likely have explored possibilities for miniaturization and simplification. Someday, when even the USB 3 specification is considered old and slow (compared to newer technology), USB 2 ports will probably not even be worth bothering with.

At this time, though, having some extra USB 2 ports can be notably handier than the other likely alternative, which could mean not having any USB ports there instead.

  • 6
    Don't forget the driving current. USB 2 uses up to 100 mA for low-power and 500 mA for high power, while USB 3 uses up to 150 mA for low-power and 900 mA for high power, with another 1.5 A or 3.0 A mode. Needless to say, those kinds of currents require a bit different design approach, and are a bit more expensive. – Luaan Aug 15 '16 at 8:51
  • @Luaan : The way I'm seeing this, you just provided actual hard numbers that demonstrate the concept I mentioned (particularly in my second paragraph). Thank you. – TOOGAM Aug 16 '16 at 2:26
7

In addition to device and/or driver incompatibility an advantage of USB 2.0 is avoiding the electromagnetic interference at high frequencies caused by USB 3.0 super-speed signaling. Intel has a white paper on the effects of USB 3.0 EMI on wireless mice using the 2.4GHz ISM band to communicate back to their receiver. The separate USB 2.0 ports on a computer case would improve the physical separation of the low-powered ISM receiver from the USB 3.0 interference source.

  • I had issues with my Logitech wireless keyboard and mouse and spent months looking for a solution. The fact that USB 3.0 is allowed despite the known issue with WiFi devices is simply absurd. By the way, if the USB 2 port is next to the USB 3 you'll still have problems. I had to use an extension cable to have the receiver as far as possible from the USB 3 ports. – algiogia Aug 15 '16 at 15:16
  • @algiogia: Your keyboard and mouse are not "WiFi devices". Have you heard any reports of WiFi (IEEE 802.11b/g/n) devices having problems due to USB 3.0 proximity? – Ben Voigt Aug 15 '16 at 15:49
  • @BenVoigt sorry Ben, I meant wireless. But yes, I've heard of some routers with integrated USB 3 port having interference problems. In any case, there is plenty of devices using the 2.4GHz band (bluetooth, cordless phones, WiFi...) – algiogia Aug 15 '16 at 16:05
  • If anything, WiFi performance will be somewhat degraded by USB 3 EMI. With the low power RF devices (mice/keyboards/bluetooth) the performance can be degraded so much by the broadband noise that communication completely fails. – user2943160 Aug 15 '16 at 23:52
4
  • More USB 3.0 add-on controllers will take bandwidth away from other parts of the system. Add too many and something will need to give out, such as running your GPU with half it's normal bandwidth or lowering internal expansion.
  • Legacy, modern Windows 8 or 8.1 tend to be happy to work on USB 3.0 out of the box (especially with the built in Intel or AMD ports) but Windows 7, various Linux distributions or tools that run outside of Windows won't always work.

It's cheaper to build a 2.0 than a 3.0.

Most devices aren't going to be able to use the speed -- mouse and keyboard, which are the two most common USB devices, won't benefit from the speed.

And, just to add this as an additional info:

Actual data throughput is usually much less than the maximum advertised USB specification.

Actual throughput in practice is typically up to 35 - 40MB/sec for USB 2.0 and may exceed 400MB/sec for USB 3.0.

Bottom line: Don't expect actual SuperSpeed data rates approaching 400MB/sec anytime soon.

EDIT

also, one silly addition

The USB 3.0 drivers must be installed before the USB 3.0 ports can be used unlike 2.0 ports.

3

Seriously ? Because a lot of good hardware was sold with USB2 support that, while possibly obsolete will be in use for another 15-20 years. There is a demand for it, it is a feature, and it will sell the box.

It is very common for older motherboards to be re-homed in new cases.

"Compatible" does not mean "Compliant". This is a weasel word.

3

USB 3.0 is electrically and mechanically different. While it is backwards compatible, motherboard manufacturers have to design for users that don't have USB 3.0 jacks on the case as well as those that do, so almost all motherboards today still have both 2.0 and 3.0 connectors to support a wide variety of old and new cases.

Users who want to maximize the number of available USB ports will choose a case that supports both, and they accept that some with be 2.0 and some 3.0.

While adaptors do exist that allow a 2.0 jack to be used on a 3.0 motherboard connector, this represents an additional expense, and the majority of customers are happy populating only the USB 3.0 ports from their motherboard, ignoring the 2.0 ports altogether.

So these cases that support both are intended for those users who want the maximum number of motherboard supported USB connectors, while still accepting that the majority of motherboards have a mix of types.

In another several years you will likely see fewer USB 2.0 ports on motherboards, just a few for backwards compatibility (driver issues with bootable media, mostly), and everything else will be USB 3.0. Cases will follow suit. Until then, you're going to see this somewhat odd mixture.

3
  • Motherboard chipsets can't handle USB 3.0 for all the ports, so if you want only USB 3.0, you'll have only a few of them. This is where USB 2.0 comes into picture.
  • USB 3.0 has 9 internal pins, and uses parallel connection instead of USB 2.0's serial connection. So it's more expensive to manufacture than USB 2.0, and non-storage peripherals (like keyboard, mouse, speakers, don't 5 Gbps bandwidth at all)

USB 2.0 pin-out:

USB 2.0 pin-out

USB 3.0 pin-out:

USB 3.0 pin-out

Notice the USB 3.0 pin-out: Pins 1-4 carry the same signals as USB 2.0 and are physically equal to USB 2.0 in terms of physical location... This is why USB 3.0 is backward-compatible with USB 2.0, although it's originally meant for high-speed storage (as indicated by the 5 extra pins on the other side, in the USB 3.0 pin-out)

  • And finally, older motherboards, their connectors, and their chipsets, don't support USB 3.0 at all! Agreed, you can use USB 3.0 - USB 2.0 adapter, but if you're going to use it at USB 2.0 speeds anyway (with the 5 extra pins idling) you are better off using USB 2.0 natively!

EDIT- Some keyboards do use USB 3.0 jacks, but only because such keyboards are equipped with a USB pass-through mechanism - there are USB 3.0 ports on the keyboard itself, so you don't need to reach your computer case, every time you want to plug in your phone or a flash-drive.

2

I have a very good board, it has 4 USB 3.1 ports in the front, 8 3.1 ports in the back, 2 USB 2.0 ports in the front, and 2 USB 2.0 ports in the back.

The documentation that came with the board suggest two important uses for the 2.0 ports, and their inclusion.

  1. Old devices and Old drivers. If a device is old enough then it may not work in USB3.1 ports. Mostly because that device "sucks" and didn't follow the specs, but also because maybe it was created while the spec was being adopted.

  2. Voltage and Amperage differences. USB 2.0 has different maximum amperage profile. On some devices this can make a large difference.

The document then suggests some things for using different ports. For example.

USB 3.1 ports should be used for

  • Charging a phone or tablet
  • high speed data devices like harddrives
  • network adapters
  • audio stuff

USB 2.0 ports should be used for - Keyboards and mice - slow data like SD cards and thumb drives - Bluetooth adapters. - Really old devices (USB 1)

It also mentions that you should try to plug "always" devices (like audio) and "sometimes" devices (like keyboard) into different controllers. And, that high data devices should not share the same controller when possible.

1

Not really an expert on USB but I've had some micro-controllers not work over USB 3 whereas they work fine over USB 2 (in this instance its connecting them to a COM port for debugging and pushing code onto them)

1

This is actually a more complex issue than one might think. I can recall asking several Hewlett Packard design engineers why their Windows servers still had floppy disk drives in 2006.

Note that Apple has the luxury of being able to drag their customers into the present whether the customers are willing or not. Vendors who sell Windows computers cannot do that.

Part of the reason Windows computers have decades old legacy features is because Microsoft found (by accident) that they could beat IBM competitively by offering support for obsolete technology. In the 1990s there was a huge demand for support of obsolete technology that IBM ignored to its detriment.

This problem has persisted to the present and there seems to be no solution - except perhaps to buy Apple products. Note that Apple is apparently about to eliminate the legacy audio port on its iPhones. The negative response to this is incomprehensibly overwhelming. Note that this is insanely obsolete technology.

I have discussed this problem with many highly intelligent individuals working for Intel, IBM, HP, Dell, etc. Generally system designers feel trapped by this issue but know of no solution.

0

Some software will not recognize 3rd party USB 3 drivers in Windows 7. This will be the case even if the drivers are fully functioning.

For example, I have a 2013 motherboard which was top of the line for desktop systems at the time I got it. I run Windows 7 on it with the manufacturer's drivers installed.

The USB 3 devices plugged into USB 3 ports are recognized and function correctly. But when I run VMWare Worstation 11 on it, it does not see USB 2 or USB 3 devices plugged into USB 3 ports. The same devices are recognized by VMWare workstation on a Win 8 laptop when plugged into USB 3 ports. And the same devices are recognized by WMWare WS 11 when plugged into USB 2 ports. If the motherboard did not have USB 2 ports, I would not be able to pass through to the guest OS any USB devices at all.

VMWare did start supporting USB 3 devices under Win 7 starting with WS 12, but it came out only in 2015. But I haven't tried it. And I don't know if it will support the particular 3rd party USB 3 drivers which I have.

From a developer perspective, I have to mention that USB 3 ports are functionally very different (it's not just a difference in speed) from USB2. So the decision not to provide generic kernel-mode USB 3 drivers in Win 7 may have more to do with how the USB driver framework was designed in Win 7 vs Win 8. If the whole framework would need to be overhauled in order to support the drivers, then MS was probably justified in asking that a later version of the OS would be used.

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