Hi A funny little question that bothers me is how does the computer know when the ink is about to run out on a printer? Does the printer have a sensor on the inktank or does the computer just take note of everything that is printed and which colours is used etc and estimate when it will run low based on how many times you have printed? My printer is Canon i450 Cheers for any input

Excellent question Vince!!!

My HP inktanks should have a sensor (with build in print heads it shouldn't be a problem!) and I've also seen a black one on a friends HP printer that even showed it on the outside of the tank! The Epson printers I know don't have a sensor on the tank (no contacts) so it has to be something else. Maybe the pressure of the remaining ink ???

Epson printers have what they call a "smartchip" on each cartridge that constantly measures ink quantity and gives you a graph as the ink is consumed. Epson also has a lot of bad-will earned, because ONLY Epson carts have this chip and when it registers empty the chip shuts down. So, you cannot refill, and you cannot use a generic-only Epson. AND you only get 50 sheets from each black cartridge, AND each cart of black costs-get this-$34 (include tax). That translates to $0.70 per sheet of text printed. Color carts are smaller, so actually cost same/higher. Don't get Epson!

Hmmm from what Im reading here the canon printers must do a simalar thing but there is no contacts on the carts for data transfer so im thinking that the computer must keep a table of how many drops of each colour is used and calculate it on that, as manufactures would know exactly how many drops are in the tanks to begin with, Cause if I open my lid and close it ,y printer drivers ask me if I replaced any tanks while the lid was open.

Hi Everybody. Canon printers have an optical sensor. I think that means when light shines through a certain area of the cartridge, the printer indicates low ink. This is from a review of one of their inkjets. "The printer uses a simple, optical ink level sensor that gives accurate feedback without the cost of 'intelligent' cartridges. The result? No more wasted print jobs. No more wasted ink! High quality, vivid prints." Take care, Linda