why isn't it ok? why????

Huh, I'm not sure they are comparable.

Didn't USB A and USB B use a master-slave relationship in which the ~~male~~ USB B would (generally) always be the slave, whereas USB C uses agreement and discussion to decide the master and slave roles regardless of connector gender.

Please do correct me if I'm wrong. Also, do we say "agent" now instead of "slave", or what is the new term?

I believe the common terms now are "domme" and "sub"
- I can't tell if this is real life or sarcasm....
  Did I really miss the memo on this one?
- I'm going to refer to myself as USB-B from now on
I think the biggest problem I see with A to A is: who's delivering power, and who's receiving it? Maybe if you use it only with the device it came with then it'll be fine, but if anyone tries to just hook up that cable to two random computers, it might actually cause a short circuit and fry something.
Whereas Type-C was explicitly made to handle such situations.
Or a shorter reason: Type-C cable is allowed by the spec while Type-A is not.
- Hrm. I have a keyboard that requires an A to A cable and I think it works with the cable any way around...
  Might be wrong.
- I've actually used this to my advantage. I bought some cheap speaker/light combos which basically made the lights dance to the music. The only power connector was a wire that comes straight out of the device and into an outlet. But it did have a USB port for loading music from a USB stick. So naturally I plugged one side of a USB A into the port and the other side into a power bank and it just straight up worked.
master/slave could be primary/secondary, primary/subordinate or principle/agent, so you're correct on that replacement.
I personally am a big fan of "Mantrap" becoming an "Access Control Vestibule" mostly because it's fun to say.
- I like controller/peripheral, which is the most descriptive in my opinion. That's what's commonly used for SPI.
- I've been using parent/child, I guess that's not always correct?
In the usb world its "host" and "device", not "master" and "slave".
But yes you are right
Both ends of a USB cable are generally male (unless you're talking about an extender). Generally the type B end (in mini, micro, or full configuration) would be the client though I have seen a couple of clients use Mini or Micro A.
Yeah we’ve been going by primary-secondary where I am for the just 6 to 7 years now but I don’t think a universally agreed replacement for the terms exists yet.
Mechanics are still trying to figure that out with the "master cylinder" and "slave cylinder"
Type C sounds like a healthy relationship.
- I have a healthy relationship with my Master uwu
I think reusing server/client naming for USB connectivity instead of master/slave would fit it

USB-A male to USB-A male is not in any USB standard (not entirely true, but compliant cables are very rare and don’t connect voltage), and if you plug it into a device it’s not meant for, the behavior is entirely unspecified. It will probably do nothing. But it might fry your USB controller that is not expecting to receive voltage.

USB-C to USB-C is in the spec, and if you plug in two host devices, they won’t hurt each other. You can actually charge a host device over USB-C, unlike USB-A.

That’s why it isn’t ok. It’s not the same thing, it’s not in the standard, and it can even be dangerous (to the device).

I think the argument that A-A should be in the spec.
But usb-c is just so much better all around.

A to B made more sense in a world where devices cannot serve as both roles via negotiation. My android phone when I got it utilized a data transfer method of plugging my iPhone charge port into my Android charge port, then the Android initiated the connection as a host device.

The true crime is not that the cable is bidirectional, the true crime is that there is little to no proper distinction and error checking between USB, Thunderbolt, and DisplayPort modes and are simply carried on the same connector. I have no issues with the port supporting tunneled connections - that is in fact how docking stations work - just the minimal labeling we get in modern devices.

I'd be fine with a type-A to type-A cable if both devices had a reasonable chance at operating as both the initiator and target - but that type of behavior starts with USB-OTG and continues in type-C.

USB-A requires three attempts to connect, C only one.

Six since it has A at both ends.
- 3 for A, 5 for B.
I absolutely have some Type C cables that only work one way because there's no enforced standards and the manufacturer will wire them however is cheap, throw on another company's logo, and sell it to Amazom.
- Don't buy electronics through amazon. This is precisely why.
- I have never seen this.
  There is absolutely a certification process, but playing legal whack-a-mole with fly-by-night counterfeiters is difficult.
  \ This is why buying reputable brands from reputable sellers is important.
  But even then, I remember years ago I read an article about major retailers selling counterfeit brand name SD cards that didn't meet the labeled performance specifications and had very poor QC. Turns out that gray market sellers were buying batches of the real product that failed QC and just reselling them as though they were fine, and they ended up making their way back into the distribution network.
  \ In the end the conclusion was that we're all kind of fucked until retailers start being way more strict about their supply chains, which they are disincentivized to do, because the current system gives them plausible deniability on things like child labor.
- Gross. I haven't run into that.
I have a switch controller that requires two plug ins to work

The USB spec requires one master and one slave device, which is usually decided by which type of connector each side has. USB OTG can bypass that restriction, but I've only ever seen it done with micro USB or type C.

I actually have one of the USB A cables above from an old android tablet that had 2 full USB A ports on the side.
One was always a slave/device port while the other actually had a physical switch to change from Host to Device.
That used to be my mobile media tablet. I could cast wirelessly or steam directly from the mini HDMI port. Such an awesome device for how cheap it was.

I guess the usb spec makes you sick then.

With the the first one you can fry your gear, while stuff that takes the second one does auto negotiation.

I realy don't want a cable i plug both ends in wrong and have to turn them a couple of times

Well, if you have asymmetric cables, there's always one clearly-defined host and the other one is the slave.

it works like sex: with usb-c, both devices more or less kinda have ti "negotiate" who's dom and who's sub. that takes extra negotiation effort and makes the protocol more complicated. and therefore more expensive imo.

Just a small nitpick, but sub or dom doesn't care about gender or sex, its top or bottom you mean in your example :)
- bottom dom sounds interesting 🤔
more expensive imo.
actually the same pins (well one of them , though since the connector is rotationally symmetric you need two anyway) are used for USB Power Delivery and to negotiate what speed regime to operate in .
furthermore , USB On the go , which was introduced in USB 2.0 , offers the same functionality for USB Micro and USB Mini

I've never seen a USB-A to A cable in the wild, except recently, where I finally unpacked my SATA/IDE USB adapter from Ugreen.

They used to be moderately common in the before times, like 2.5 inch IDE HDD times.
For added horror those often where Y cables, too.
My USB KVM switch uses them
They are commonly used with USB keystone connectors. For some reason most of them have A connectors on both sides.
Most cheap usb switchers will use them on the computer-switch side. I have a few models that I was testing out so I have a small pile of these. They’re great for cutting in half and using as a small usb power supply cable to breadboard projects, along with the horde of 5w Apple chargers I have in a bin.
I've had old Ugreen devices with a similar setup. Notably a KVM that fried my keyboard bc they failed to follow USB spec.
A-to-A cables are, in general, a hardware design smell. It's best to avoid devices that don't care enough to follow the spec.

In the long, long ago, we used to use USB-A to A cables to transfer customers' Mac OS X user profiles when they would buy a new Mac. Also worked with Target Disk Mode, way back when.

I only remember doing this with FireWire. Which model supported target disk mode over USB-A?
- Ha, old man brain glitching there. The A to A cable we used for file migration, but we had to stick an A to C adapter on one end to use TDM on some machines (had to be USB 3 rated, I think). It was around 2016, if I remember correctly? It honestly didn't come up that often.
Apple didn't use FireWire for that?
- They did, but the first run of MacBooks we got that didn't have Firewire would let you use USB. But we needed an A to C adapter to make that work.

The joke is that A to A doesn't make sense.
Yeah just guessing if the cable supports the right usb-c protocol. The port is great. The protocol is horrible you have like 10 different versions of the same protocol. And you have to pray that your cable supports the right one you need.
The joke is that USB-A shouldn’t be paired with another USB-A. It should be using a USB-B on the other end. USB-A to USB-A could potentially be damaging, as both devices will expect to be providing power. USB-B denotes that a device is “receiving” USB, not “sending” it.
USB-C is an absolute shit-show. Half a dozen types of identical looking cables all with different performance and compatability. They can be power only, USB-2 only, USB 3, 3.1, 5gb, 10gb. Some can carry 5A, others only 3A. Some may support thunderbolt. Cable sellers and manufacturers can/will claim anything.
For people selling USB-C devices it's a massive support problem. It looks like the device is defective, but someone may just have swapped out the cable for their phone charger cable and there's no way of telling.
It is a fact that USB-C is superior.
The floating tang in the center of the USB-C receiver is a classic "planned obsolescence" design feature. Its built to fail and force you to buy a new device.
- Source on this?

What's a common thing that would require the use of USB A on both ends?

The only place i ever saw it was on those cooling padas for laptops
it was common amongst digital cameras in the early 2000's.
and maybe you could somehow link up two computers as well...? tho that could have been some specialized cables
- They make A-to-A cables with a bit of file transfer software integrated into the cord. Useful for transferring big files between two PCs without setting up a network.
nothing worthwhile, as it's not allowed (for a good reason)

Who are these people?

What if I put a C-to-A Adapter on both ends? Is that okay?

C to A adapters are sick and illegal
I still have some
- Why would that be illegal? Shouldn't there be some way to plug an older flash drive or console cable into a laptop that doesn't have a type A port? (Ahem, Mac)
Yea but it's inefficient. USB-A has a significantly lower transfer rate than USB-C so it'll bottleneck

actually they would be correct :

USB began as a protocol where one side (USB-A) takes the leading role and the other (USB-B) the following role . this was mandated by hardware with differently shaped plugs and ports . this made sense for the time as USB was ment to connect computers to peripherals .

however some devices don't fit this binary that well : one might want to connect their phone to their computer to pull data off it , but they also might want to connect a keyboard to it , with the small form factor not allowing for both a USB-A and USB-B port. the solution was USB On-The-Go : USB Mini-A/B/AB and USB Micro-A/B/AB connectors have an additional pin which allows both modes of operations

with USB-C , aside from adding more pins and making the connector rotationally symmetric , a very similar yet differently named feature was included , since USB-C - USB-C connections were planed for

so yeah USB-A to USB-A connections are explicitly not allowed , for a similar reason as you only see CEE 7 (fine , or the objectively worse NEMA) plugs on both ends of a cable only in joke made cables . USB-C has additional hardware to support both sides using USB-C which USB-A , neither in the original or 3.0 revision , has .

With USB-C isn't there still a slave-master dynamic that is now negotiated via software rather than hardware?
- a slave-master dynamic
  please don't use that term, every time i see it i immediately verge on orgasming. you've already made me ruin 2 undergarments today. i have a serious bdsm kink and this is not funny.
- it seems like it , but I have no idea !
  edit : to clarify , I believe it does , using the CC1 & CC2 pins which are also used for other things , but I don't know anything about USB protocol side , I should learn about it haha

It's about the winding and not about the USB version, right?

I have an external 3.5“ HDD enclosure that has a USB-A port to connect the usb cable to. I have no idea who thought that was a good idea. The difference in price to a B connector can’t be that significant…

I have a similar PATA enclosure. I thought it was cursed until I got to reuse the A-A cable to upload FlashFloppy custom firmware to Gotek floppy emulators without wiring up a USB-serial adaptor.
You underestimate what price difference is significant in some cases. If it is even a tenth of a cent cheaper, it is decided.
- I know, but it shouldn’t matter. Also, it feels like the amount the A port is cheaper an A to A cable would be more expensive

I'm not sure what the point is here. C is symmetrical and has absolutely no downsides, so yes, it's objectively better.

I am a stupid end user. But I've never found an instance where I needed male to male cords.

In general? Off the top of my head I remember these male to male cables.
Ethernet cables
telephone cables when they were a thing
audio cables of different varieties
optical cables
coaxial cables when they were a thing
You've never used HDMI?
- My usb-b monitor stands alone
Chargers are now female. So you need m2m to charge your phone

My WH1080 weather station has a USB-A connector on the device side, I assume for the convenience of the slimmer profile.

That's the only natural occurrence of that cable I've ever seen.

The other one was a custom board printed in 2001 at the electronics class, where I was some kind of precursor by powering it with a USB cable rather than a bulky lab power supply. As I did salvage the connector it was a A-A abomination but they had that cable at the supermarket for some reason ¯(ツ)_/¯

If you go buy one of those laser engravers off of eBay, for some reason their data in ports are USB-A, and they come with USB A to A cables. My understanding is you can both plug it into a PC and run it kind of like a printer, click Print and the machine jumps to life, or plug in a USB key with tool path profiles on it to use standalone. Why not have a USB-B port for device mode and a USB-A port for host mode is beyond me, I don't live in Shenzhen.
It is expected to be rare, since A to A cables are out of spec.

I read the Wikipedia a little and apparently A to A cables can damage your devices, and the ones that do exist are for specific purposes and should only be used in those specific scenarios, and often they are more than just cables and have some computational stuff inside them

I actually found an A to A cable in my Big Box of Cables I Might Need One Day™ when trying to flash my Gotek floppy emulator with FlashFloppy firmware.

Why?
- For the glory of Satan, of course!
- Hub switches, for one. Power is another (usb a is easier to solder on by hand, as well as cheaper)

We peaked at USB mini B.

As it being disgusting or great?
- Objectively disgusting. How can one connector be so chunky while still being asymmetric?

I actually have a double sided male A cable. I was shocked when I got it but I have this laptop cooler that has two A ports on it, presumably to allow a pass through but I'm always nervous that I'll plug it in and fry something.

Cut it in half and avoid the spec violating abomination.
You'd probably be able to remove the cooler's non-compliant a-port and just solder the cable directly.
Then at least it'll be less of an abomination.

I actually thought this was about rolling up cables: circling on the top and over-under at the bottom

If I remember correctly you can't do data copy with A to A. I maybe wrong but I'm to lazy to look up.

I bought a charging pad once that had a USB c connector but none of the 40 USB power adapters I have have one so I returned it. IDK wtf they were thinking. Just make the wall end an A connector like everyone else has been doing for a decade.

USB-C can deliver more power which is why they've been appearing more and more on charging bricks.
- I had to look up, USB PD does work with a USB A port.
  That being said, I personally want to get to a single type of cable so any I get can be spares for anything I have, so I like USB c to be all around.
  That ALSO being said, I doubt I will ever get to all USB C.
  Side note, USB PD is awesome because I know it can do up to 240w. (Last I knew.) That is 48v at 5a, so I am not sure what they can do to squeeze out more wattage.
- C-C carries more power than A-C?