Inches vs. Pixels in Photoshop vs. InDesign

Question

I'm confused.
I told InDesign to make my page size 600 pixels by 800 pixels. I then changed the ruler to show inches. It showed the page size as 8.333" x 11.111".
Then I told Photoshop to create a canvas size 600 pixels by 800 pixels. When I changed the ruler to show inches it told me the page size was 2" x 2.667".
Why the difference? And if I want to create something that is 600 pixels by 800 pixels, which do I believe? I am creating an epub and want a cover that is 600px x 800px - I can create in either INDD or Photoshop, but don't feel confident that it will be the proper size.
BTW, I'm using CS5 for both products.
Thx for your help,
Sandy

Answer 1

The reason you would set the file resolution to anything other than your monitor's resolution is that in the long ago bye bye, before the interwebs, but after stone tools, there was something called PRINT. It was a poor, analogue medium that required participation of the consumer, what you might now call interfacing. For instance, the user would have to HOLD the printed object and move it toward and away from his face. Instead of clicking, the user would have to employ his opposable thumb and and a finger to grab a PAGE and turn it to the next one.
Images were PRINTED in PRINT and  were composed of HALFTONE DOTS. How many DOTS PER INCH could determine how many shades of gray could be represented, and gray could have color substituted. Overlaying 4 of these grids of colored dots could create a crude color image. It turns out that in the way back, at the peak of this archaic technology, a grid might be able to put 170 Dots Per Inch, or more, on a PAGE. While still crude in modern terms, this pleased the people of that day.
As the light of digital technology dawned, old tech and new overlapped a bit. So, for a while, it became a standard, out of laziness mostly, that 300 PIXELS PER INCH was the sweet spot to create most HALFTONE GRIDS. If a "Graphic Designer" wanted a pretty picture with sharp lines printed in a "magazine" with a HALFTONE GRID at 150 Dots Per Inch, making a Raster Image of 300 pixels per inch worked just fine. So for many of us Neandethals still allowed to live in this modern age, many of us hold on to comfortable old things from Days-Of-Yore, such as knowing exactly what resolution works optimally for which dot pitch so our work that gets PRINTED works well. We still enjoy complaining to a PRINTER (a person with ink in their blood) about the CYAN plate drifting out of registration over the course of a print run. Then we go off the Renaisance Faire.
Craig