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Ipac Usb Vs, Ps/2
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SunnyDU:
You may be missing my greater point.  I could care less whether PS/2 ports are obsolete or not regardless of how Webster defines the word.  My interpretation of the prediction was that the mass market would not be using the PS/2 port anymore and that this prediction was very relevant to main topic/question originally posed 10 years ago.

My statement was more calling attention to the irrelevance of the ubiquity of the PS/2 port in relation to the topic/question.

I'll side bar for a second though and disagree that simplicity is the reason it's still around.  The reason is lives and will continue to live in specialized markets is entrenchment.  The market doesn't care about simple, the market cares about making money.  As long as there's a market for it and the cost continues to be justified, PS/2s will still be available.

I'll finish by repeating my question. Is there are still differing opinions and/or facts on the performance of each given today's technology and what should now be provable historical evidence of performance metrics of each technology (PS/2 versus USB).  Please continue to assume that the system this is running on is a dedicated arcade cabinet with no other USB relevant devices connected.
AndyWarne:
We will be dropping PS/2 support on the I-PAC range in a couple of months. The only reason we have kept it going is owing to a false belief that PS/2 is better than USB. Its not. PS/2 is obsolete, end of story and from a purely technical point of view we should have dropped PS/2 support years ago.

The DOS argument doesnt stand up because if you are using DOS on a modern motherboard the PS/2 issue is the last of your worries, DOS is terrible on modern hardware both in terms of I/O and video performance.

Motherboard manufacturers have propped up PS/2 support by tacking it on as an afterthought onto the ACPI power control subsystem and its implementation is poor and has been for years. Windows support of it is also poor. The PS/2 interface has not been maintained as any kind of standard for years since IBM disowned it and incompatibilities are rife.

I was involved a couple of years ago with a project for a bank data entry center which used PS/2 keyboards. They replaced all the PCs with Dells which were the last ones to have PS/2. The keyboard performance was so bad that they had to junk them all and replace them with new USB ones.

USB out-performs PS/2 by a huge margin and nobody should be using PS/2 for gaming on modern OSes or hardware.
RandyT:
PS/2 is a true serial interface, with regard to individual keypress events, while USB keyboard devices are not.  USB input events are packetized, and not necessarily acted upon by the system in any specific order if received within the same packet.  The only reason this doesn't matter with keyboards is the fact that it is extremely unlikely that a person typing at a simple keyboard will be typing fast enough to cause multiple input events to occur within the same packet.  This is not the case where keyboard technology is used as a gaming controller, and multiple events can be occurring across several users, nearly simultaneously.  When this occurs in the case of fighting games, when one player executes a move a tiny fraction of a second before the other, there is no guarantee that the player who actually executed the move first, will actually be given priority.  In devices where multiple keyboard devices are reported by the same physical device, this can become worse if that player's input happens to be relegated to a different keyboard device than the one being reported next.  This is, of course, dependent upon the implementation, but users have no knowledge of these kinds of things to know exactly what workarounds are in use to get past simultaneous keypress limitations.  It can be done well, or not well at all.  This is not the case with PS/2.

For bank data entry and Point of sale, PS/2 was the norm for just these reasons.  The devices used were often piggy-backed onto the keyboard data stream, which meant that to the system it was attached to, it appeared as though the user had actually typed the data, albeit very quickly, and the data order would always be correct. 

For arcade gaming, the PS/2 protocol works perfectly.  It is way more than fast enough for the 60hz polling cycles of arcade games, and it is extremely reliable.  In fact so reliable, in cases where users have issues with using USB on some of the dual-compatible devices, the first suggestion is to use the PS/2 capability if present on their system.  When that advice is followed, their issues seem to go away.  That alone tends to speak volumes in support of using it, if one can.

As for it being an "afterthought", I find it odd that one would think a special two color connector to indicate either mouse or keyboard compatibility, and appropriate connection to support both without interference, was an afterthought.  It seems pretty well thought out and implemented to me. 

BTW, Dells are the oddball when is comes to keyboard issues.  Every time I have heard of an issue with a keyboard, the name Dell always seems to pop up.  Not with all of their systems, mind you, but they dropped the ball with some of them, even to the point where they were very picky about even regular keyboards working, when it did not carry their brand name.
SunnyDU:

--- Quote from: RandyT on September 22, 2014, 01:49:29 pm ---When this occurs in the case of fighting games, when one player executes a move a tiny fraction of a second before the other, there is no guarantee that the player who actually executed the move first, will actually be given priority.

--- End quote ---

Wouldn't that depend on how the encoder handles the buffering? Couldn't the encoder guarantee order prior to sending by not "packetizing"?

Either way, seems like both sides of the statement could be provable with some asynchronous testing and metrics for out of order hits or something similar.
AndyWarne:

USB wins in fighting games owing to the need for detecting complex moves involving simultaneously pressed keys whereas PS/2 is a slower serial interface.

In spite of the PS/2 interface being simple at the hardware level, the data still has to get through all this lot: http://msdn.microsoft.com/en-us/library/windows/hardware/jj128267(v=vs.85).aspx

At the end of the day the game is the limiting factor in determining whether very closely-spaced keypresses happened at the same time or not, and would have trouble with either interface. USB is certainly not an issue in this respect as the packet rate is faster than the poll rate of the game. The original hardware would poll the input bus receivers at a certain rate and read all pressed keys at the same time. This is closer to USB in which all pressed keys are sent in one go.

I am not going to debate this any more because this debate has gone on longer than it should already. Much like the PS/2 interface itself :)
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