I have been wondering about single touch/multi touch technology for a bit recently. I was wondering if it is hardware or a software limitation. I have heard that android is currently single touch but that the software will be updated so that it will become multitouch, and I was wondering if this will change the G1.

But what I have really been thinking about is the n800 and if it is software then the touching on the screen is essentially acting as a cursor or mouse input? Or is it a hardware limitation? If its a software limitation is it something that could be fixed or would be part of the propriety software that users do not have access too?
I have a feeling these are probably silly questions but I believe they are worth asking.

its both, altho primarily hardware, as it need to be able to register and report multiple coordinates.

the software then need to take these coordinates and make use of them...

Google for 'how to make a cheap multi touch device' or something like this. You can make this with a simple webcam and cheap materials.

It still depends on the hardware though. I don't remember exactly why anymore, but I remember not every touch screen is the same under the hood. What I remember is that it can be magnetic, but also that it can use a camera in the back to register touch.

Ofcourse, the software also has to understand multiple touchings and provide a framework (API) to use the input. This is the most complex part. See also Wikipedia entry.

There are basically two wide spread technologies for touch screens. One works by the electical resitance of thin plastic layers on top of the screen. This is what the tablets use. It's precise, but cannot detect multiple touches (as is just measures one resistance per direction).

The other type works by measuring electrical capacity from below the lcd screen and can detect multiple touches. But its resolution is limited and its thus mainly used on devices that use this for a finger touch screen where accuracy to the pixel is not required. The iphone uses this.

Also the latter one is more robust as the sensitive part does not consist of a thin layer on top of the screen.

People have however tried to emulate multi touch with resistive screens ... with limited success ...

Or, you can have both (called dual digitizer).

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tso's post underneath this one is talking about your standard Wacom tablet.

They are very accurate, can detect things like pen tilt and distance from surface, pressure, etc. Also, they are very expensive.

there is also the option of having a "active" stylus, that either via a static charge or battery interacts with a sensor in the display/surface.

I know there was some experimentation with this in liqbase that was quite impressive, but I don't know how far along lcuk got in implementing it practically or what sorts of problems arose from it...

21 finger gestures, anyone?

Ummm, 10 fingers, 10 toes, and a tongue?

This is a nice history of multitouch.

http://www.billbuxton.com/multitouchOverview.html

IIRC, according to Nokia, multitouch is defined as where the touch screen is contacted at a first point and the contact moves to a second point where it is released and so most HW is capable of multitouch according to this definition. This would mean the first handheld communications device with multitouch was invented by Nokia (not iPhone) in 2004.