[OT] Why does X need so much CPU power?

[Neal Lippman <nl@lippman.org>]

I'm just wondering if anyone has any info on why X seems to need so much
CPU power?

Way back when, probably around 1996 or 1997, I first tried to install
Linux. Back then, I tried distro's from Corel and Redhat. My system was
a Pentium 133 with 48 (and then 96) MB Ram. This system ran both Win 95
and Win NT 4.0 reasonably well, but when I made the switch and installed
Linux, any sort of desktop - eg Gnome or KDE, not a vanilla WM) was just
so slow as to be unusable. Eventually I gave up for a while and went
back to WinNT for some time.

For the past 3 years or so, my workstation has been exclusively Linux,
first Mandrake on a PIII-800, and for the last year, I've been hooked on
Debian on an Athlon XP 1700+, and on both of those systems performance
has been just fine, so I didn't really think about the troubles I
originally had, and when I did, I figured I must have done something
wrong on my first install attempts on the Pentium system.

A few months ago, I decided to put debian on my old Laptop, an IBM
Thinkpad 770ED (PII-266, 64MB Ram). Once again, with KDE running, the
desktop was so slow and unresponsive as to be really unusable (except in
an xterm window). This is a system that has run Win95, Win98, and WinNT
just fine over the years.

So, my question is: Why does X seem to need so much more CPU power than
windows - such that systems I have tried to use that worked fine with
various windows flavors just were unusable with KDE loaded? I assume the
problem isn't in Linux itself, since my old Pentium 133 was just fine
with X not running, and enough people have attested to the ability of
systems with Pentium processors running Linux without X being able to
handle massive firewall, router, web server duties, etc. Maybe the
problem is KDE and not X - but I had similar trouble with Gnome, so it
isn't just a KDE issue.

I'm just curious and wonder if anyone has any thoughts.

Thanks.
nl