why is a bootloader required?

From: funkymunky (prehistorictoad2k_at_yahoo.com)
Date: 12/31/04 

Date: 30 Dec 2004 23:40:31 -0800

Hi,

Im new to the arm family and embedded systems in general,till now iv
worked a bit on the 89c51. Ive been puzzled by the following: why is a
bootloader required in controllers like the at91rm9200 im using right
now? how come no bootloader is required in a controller like the 89c51?
Iv read a bit on
the need for a bootloader in a PC..but why would it be required on a
controller?

Also, the atmel manual mentions that a default bootloader is provided
in controllers like the one im using..my project involves porting of
Linux to this controller..why,then, is a seperate bootloader reqd??
thanx in anticipation
Mayank