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USB keyboards and cpu?

post #1 of 2
Thread Starter 
Do USB keyboards really use up more cpu cycles than ps2 ones? This is not about a difference in practice, does it or not?
post #2 of 2
It does because when a keyboard is connected to the USB port, the keyboard is being polled so that when a keypress is sensed, an interrupt request is sent so that your keypress registers just as you expect it to. So when you press a key, it goes "I just sensed a keystroke! Send an interrupt request immediately!"

But when a keyboard is connected through PS/2 (even through a USB to PS/2 adapter, if the keyboard works through one of those), it's not being polled at all. Instead, every single keystroke sends an interrupt request.

So polling consumes CPU cycles, constantly monitoring the keyboard for any keystrokes. It's nothing to shake a stick at, but it's still happening. Plus, it's possible for a USB keyboard to be slightly interrupted by other devices connected to one of the other USB ports. But when it's connected to the PS/2 port, it's perfectly isolated and it gets all the attention it wants every single time it wants it.

Fortunately, it doesn't make a noticeable difference on a system like yours or mine, so it's not really a valid concern. But for purists, it's almost fun to prefer that the keyboard is connected to the PS/2 port. That way, the only thing that's being polled is the mouse, and that's actually preferred for superior mouse performance.

But ultimately, the main benefit these days is N Key Rollover with mechanical keyboards that specifically offer it. But even that's slowly changing.
Edited by TwoCables - 3/10/11 at 10:16pm
It's a computer!
(19 items)
 
  
CPUMotherboardGraphicsRAM
i5-2500K @ 4.5GHz (1.368-1.384V fixed voltage) ASUS P8P67 EVO B3 (UEFI ver. 1850) GTX 780 ASUS DirectCU II (1228 / 6300, 1.180V) G.SKILL Ripjaws X 8GB (2 x 4GB) 1866MHz, CL9 
Hard DriveHard DriveHard DriveOptical Drive
250 GB Samsung 840 EVO (C:\) 250 GB Samsung 840 EVO (D:\) 150 GB WD VelociRaptor Samsung SH-S243N 24x DVD Burner 
Optical DriveCoolingOSMonitor
Samsung SH-S203N 20X DVD Burner Thermaltake Frio Win 7 Home Premium x64 SP1 Retail AOC G2460PG (24" 1920 x 1080 144Hz G-SYNC) 
KeyboardPowerCaseMouse
Filco Majestouch 104-key Cherry MX Blues w/NKRO Corsair HX650 (Bronze, ordered on 12-12-2009) CM 690 Intellimouse Optical (1.1A) 1000Hz polling rate 
Mouse PadAudioAudio
Basic, but premium round X-Fi Titanium HD Klipsch ProMedia 2.1 (with 16 AWG Monster Cable... 
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It's a computer!
(19 items)
 
  
CPUMotherboardGraphicsRAM
i5-2500K @ 4.5GHz (1.368-1.384V fixed voltage) ASUS P8P67 EVO B3 (UEFI ver. 1850) GTX 780 ASUS DirectCU II (1228 / 6300, 1.180V) G.SKILL Ripjaws X 8GB (2 x 4GB) 1866MHz, CL9 
Hard DriveHard DriveHard DriveOptical Drive
250 GB Samsung 840 EVO (C:\) 250 GB Samsung 840 EVO (D:\) 150 GB WD VelociRaptor Samsung SH-S243N 24x DVD Burner 
Optical DriveCoolingOSMonitor
Samsung SH-S203N 20X DVD Burner Thermaltake Frio Win 7 Home Premium x64 SP1 Retail AOC G2460PG (24" 1920 x 1080 144Hz G-SYNC) 
KeyboardPowerCaseMouse
Filco Majestouch 104-key Cherry MX Blues w/NKRO Corsair HX650 (Bronze, ordered on 12-12-2009) CM 690 Intellimouse Optical (1.1A) 1000Hz polling rate 
Mouse PadAudioAudio
Basic, but premium round X-Fi Titanium HD Klipsch ProMedia 2.1 (with 16 AWG Monster Cable... 
  hide details  
Reply
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