They go through to different circuitry. Look, you could say, why have any standard connector at all when all you have to do is hook up some jumper cables? After all, all you have to do is make sure you never, ever, wire anything up wrong or to something it should not connect to.
So…you have exactly the same four wires in USB-A and USB-B. The difference is the plug shape and wire arrangement.
But we need USB-B to make sure things go right because why?
Same wires. Why can’t manufacturers manage to cope with USB-A?
You’re asking why manufacturers 30 years ago couldn’t cope with it, right? Because, now you have what you’re looking for – USB-C, same at both ends.
I imagine it was a lot cheaper to make either host or peripheral units, rather than having every device being able to negotiate its status and power needs, back then.
I beg to differ. There’s one beside me right now. I checked a bunch of new printers, and while most have Wi-Fi connectivity, every one also had USB. What nobody uses any more is the huge Centronics-type parallel printer cables, or RS-232 serial cables.
Yes, I was going to say, that plug-and-play technology is USB-C (and I have heard occasional stories of it glitching out!), so you may as well ask why they bothered with USB-A/B at all when they could have simply invented USB-C in the first place.
I’m wondering why old Bell telephones ever used the big four-prong plugs, or even the smaller RJ-11 connectors, when they could have used USB-C.
They absolutely still use stuff like that, just not on your laptop. RS-232 and RS-485 and stuff, anyway.
My friends, too. But our friends are probably more technically inclined than the general population.
Oh, sure, they could. But then, instead of needing a really common cord that you probably already have and could certainly buy from any computer or office supply store, you’d need a really rare and unusual cord that almost nobody has. How would this be an improvement?
I went digging through my box-of-random-crap where most of my cables go and while A-A is not there I do not have A-B either. Seems I have every other possible combo but not those. And I have a LOT of cables (thinking I need to get rid of some now I look at it).
A-B may be much more common but still…not common enough that I have a half dozen in my box of stuff that seems to have every other kind of cable collected over 25 years.
@Whack-a-Mole I made the claim that standard B is “more robust”. I suggested a way to assess it yourself. Did you try that? Do you have some other reason to call my claim “ridiculous”?
As an aside, I didn’t know about USB 3.0 Standard‑B.
Yes…I mentioned that printers are almost never moved. Ever. They are bulky and generally heavy. Not a thing you just move around on a whim.
Also, in my early career, I was IT support and was the guy to move a printer if it needed moving in a very big company. I can tell you moving printers almost never happened.
A “robust” printer connector was never, ever, on our minds. Ever.
The choice of a printer connector was not whether it was “robust.” Although, to be fair, back then they were parallel connectors and screwed in so different time.
I have quite a cable collection. I have about 10 USB-B cables, 8 mini-Bs, 12 micro-Bs, and 6 Cs (actually more Cs than that because several are in use around the house). All with A on the other end of course. I don’t have any A-to-A cables, and I’ve never seen one in over 40 years of working professionally with computer hardware. If I bought a device that used an A-to-A and didn’t provide it, I’d be royally pissed.
A few months ago I finally convinced myself that it was ok to trash my box of VGA cables. I still have a couple of dozen RCA cables even though I haven’t used one in years.
It’s not to handle printers being moved around; that was not my claim. The fact that printers are connected once and forgotten about means that users can accept, actually want, a more mechanically robust connection than something like a phone or watch.
Mini-B, Micro-B, and C all fit loosely and wiggle. They have a tendency to come loose and stress the PCB they are mounted on. Printers are physical accessories that rattle and shake, and having a mechanically robust connection is important. They are often located in awkward areas where re-fitting a disconnected cable is annoying.
A-to-A is a non-starter as discussed at length already.
Um, I doubt you bought it from them. Their motive was absolutely not to extract a little extra money from you.
That’s fine, if you prefer a cable, they gave you that option. I’m just saying that it’s silly for them to convert to the latest greatest cable when the one they are using is physically superior for this use case, and very few of their customers even care.
And the two ends of a standard electrical power cord are “the same”, but standard cables have two different ends for reasons that have been mentioned several times in this thread. It’s just two different ends, to force people to use cables in a way that’s a lot less likely to destroy their stuff.
Well, USB-C cables are rather fragile. Surely you’ve had one or two crap out on you already. If not, I’m sure several of us can testify to that. (raises hand.) And while it’s nice to have a tiny cable on a phone, a printer is a giant piece of hardware. There is more than enough room for the USB-B outlet, which isn’t really all that large. And the cables are still cheap and widely available.
https://www.amazon.com/clp/sr?clpRedir=Y&k=usb+a+to+b&channelId=500
https://www.crutchfield.com/shopsearch/usb_cable.html?fa=1#&nvpair=AG_Connector%20Type|FFUSB_Type_B
Which is evidence of how robust the connection they have is. Because if it weren’t robust, it would have to be on your mind.
In addition to moving them, and the devices themselves vibrating, people tripping over cords is a thing that happens sometimes, too.
They appear to still be used for specialized applications. And it’s not just about laptops – none of my desktop computers have any of those connectors, either. I seem to recall that a home-built computer my son and I built decades ago came with an optional RS-232 card (I think as part of the motherboard kit) that you could install or not, as you saw fit. We did not.
My newest desktop computer has no such ports at all, but is absolutely festooned with USB 2 and USB 3 ports front and back. One of which is used for an HP Laserjet printer. Another couple for keyboard and mouse.
I am still not sure why. USB-A → USB-B is the same thing. Just a different plug shape. Same wires. Same ability to suicide. Why is this special?
The -A and -B connectors of legacy USB cables are different because, as has been explained multiple times, the protocols are asymmetric. The computer (host) end is actively supplying power and is also in control of initiating and controlling communication with the passive device at the other end. In classical terms, it’s a master/slave architecture, not a symmetrical one. Not necessarily a printer – all of my USB 2 external drives and HDD docking stations have the square-shaped connector. USB 3 devices have their own special connectors.
If you had a symmetrical cable, you could connect two passive devices together but nothing would work. Or you could connect two host systems together and nothing would work, either, but you might damage one or both of the USB controllers.
As has been explained multiple times, USB-A carries power.
If you had everything using USB-A connectors, peripherals would need to have the power lines “crossed-over” internally. That would be fine, but then you would have idiots trying to connect two USB-A “Master” devices together, with possibly explosive results. The solution was to have a different connector for peripherals and masters.