The 1440 is a 1200x600 DPI printer at best. It's also monochrome. Do the math:
1200*600 (resolution per square inch) *8.5*14 (maximum paper size) / 8 (1-bit representation of pixel, since it's monochrome) / 1024 = 10.5 megs. Subtract a little since you can't do borderless and voila - you only need 10 mb onboard to print a page.
If you store truetype fonts onboard, or hold the last page in memory, you can run it up to 34 megs. I doubt it's smart enough to use more than 34 megs, but you can't max that out, since the printer doesn't do onboard postscript decoding.