What uses most power in Ebook-reader aps.?

I've had this pocket calculator to 10 to 20 years:
marked "2 penlight..for over 22,00 hours of continuous use,
  -- auto shut off".

It's use for a few minutes, about 10 times a year.
I replace the AAs approx after 2 years.
I think it's got a [originally Fairchild of '70] F8 u-proc. inside.

Q.  It must be [partially] live all the time, to read the on-key,
or can a single CMOS gate acheive this ?

Q. In general what takes the most power in a Ebook-reader
which could display approx. 80 * 20 text chars ?

Q what technology display uses the least power for this 
pixel count ?

== TIA.

problems@gmail schreef:
> I've had this pocket calculator to 10 to 20 years:
> marked "2 penlight..for over 22,00 hours of continuous use,
>   -- auto shut off".
> 
> It's use for a few minutes, about 10 times a year.
> I replace the AAs approx after 2 years.
> I think it's got a [originally Fairchild of '70] F8 u-proc. inside.

My 20 year old Sharp calculator still runs on its original 2 coin cells...

> Q.  It must be [partially] live all the time, to read the on-key,
> or can a single CMOS gate acheive this ?

The circuit doesn't have to be active (scanning the keyboard), one could 
devise a circuit that doesn't use any power until the "on" key is pressed

> Q. In general what takes the most power in a Ebook-reader
> which could display approx. 80 * 20 text chars ?

I guess that depends on the e-book reader, how many times you change 
pages...etc.

> Q what technology display uses the least power for this 
> pixel count ?

ePaper or eInkt only use power when the contents are changed. Also 
quality wise these display technologies are impressive, it is very much 
like reading text from real paper. Unfortunately changing the contents 
is rather slow (about half a second).