USB optical-cordless mouse = slower computer?

dauss · June 5th, 2003, 03:53 PM

Someone correct me if I'm wrong, but I remember reading that a PS/2 is faster for a mouse than USB. Something how fast it refreshes, and USB can't keep up. Unless they make a USB 2.0 mouse, which would be pointless.

Peter M · June 5th, 2003, 07:16 PM

That's a myth. In fact, PS/2 is the much worse connection - you're on an 8-bit ISA device designed in 1977 that doesn't even do DMA.

Herein lies the reason for the adjustable refresh rates - the PS/2 port is way too slow for smooth mouse movement unless you sacrifice lots of system load. The adjustable drivers give you a choice.

On USB, you don't need the choice since we're on a bus mastering PCI device here - and that's plenty of bandwidth to allow smooth mouse movement without holding anyone else up.

So at the end of the day, the "advantage" of PS/2 port mice turns out to be a miserable kludge to keep them halfway workable.

dauss · June 5th, 2003, 10:01 PM

I found this at Tom's Hardware.
"While we are on the subject, compared to PS2, USB is a step backward for the mouse, because PS2 can handle twice as many exchanges per second. That said, quite frankly, and even though the sticklers will criticize, the speed of exchange in USB is quite adequate for a mouse. To make their cordless system even more efficient, Logitech have ensured that the data prepared for the PC is as short as possible between capture by the sensor and sending. This means there will never be a bottleneck of data, so no data will be lost. And in use, this definite improvement is really noticeable. You won't detect any lag in relation to a wired model. We got our fragger pro to play and he corroborated: "This mouse deserves the label 'Approved by hardcore gamers.'""

http://www4.tomshardware.com/consume...110/index.html

ArcticFox · June 6th, 2003, 02:09 AM

What they said isn't true. Try using a usb mouse with a PS/2 adapter, then switch to USB. Much smoother, unless your overclocking your PS/2 port's rate, the USB will be much better. It just uses more CPU cycles, though.

Peter M · June 6th, 2003, 05:12 AM

Tom's Hardware are guessing. And guessing all wrong. The legacy keyboard/mouse controller is the oldest and slowest piece of hardware in the entire PC.

ArcticFox · June 11th, 2003, 01:39 AM

Affirmative.

radio1_mike · June 11th, 2003, 08:00 AM

Would not be the first time for Tom's.

DanU · June 11th, 2003, 04:34 PM

Yup, sometimes Tom's articles are way off.

PS/2 mice default to a 40Hz refresh rate. That's why they don't seem as smooth as USB mice. You can easily correct this with 3rd party software like "PS2Rate".

USB mice refresh at IIRC 125Hz.

I much prefer USB mice. They don't take up a dedicated IRQ and you can "hot plug" them. You can also have multiple USB mice plugged in if you so desire.

In regards to "stealing" CPU cycles, I haven't noticed any slowdown when using it on my ancient K6-2+ 450 system.

Peter M · June 11th, 2003, 05:05 PM

Once again ...

Mice don't refresh. You move it, it prepares a data packet.
On the PS/2 controller, it triggers an interrupt, the CPU must come and retrieve the packet data through painstaking I/O cycles to the legacy kbd/ms controller.
On USB, the USB controller fetches the packet, places it into system RAM through bus master operation and THEN triggers an interrupt to the CPU.

Then the packet is in RAM, and the CPU can then proceed to do something with it - move the cursor, process a click, whatever.

It's event driven, not polled at a certain frequency.

All that can be adjusted (on PS/2) is how often the mouse may send a packet. More packets mean less motion delta per packet, smoother looking cursor movement, less risk of a "jerk" effect when moving the mouse fast and far. Less packets mean less system load.

On USB this is not needed since fetching the packets does not require any CPU action at all. (Handling them still does, of course.)

chunbaouk · October 3rd, 2003, 09:44 AM

can you help me? i did have a standard ps2 mouse on windows xp which is fine, moniter refresh at 85hz, mouse on standard sample rate settings with standard xp driver, however i just bought a cordless mouse (non optical) and now the rate of sample across the screen has gone down again to windows 98 style, if i unplug it and put the corded mouse back in, back to smooth again, is there any kindof file i can get that filters the movent so that it is smooth with the packard bell cordless mouse? or a patch?