SDRAM and NAND Flash

Dear SIr,
 
I am new in this subject and concept.
i am looking for sequence of booting linux on s3c2440,
 for example what ‘s task of SDRAM? what ‘task of NAND Falsh?
 
what is different between SDRAM and NAND falsh ? NAND flash is like HDD and
SDRAM like RAM in PIC ?? what information save on NAND falsh and what
information save on SDRAM ?
 
please help me 

thanks

NAND is flash and SDRAM is RAM.
Difference of flash and RAM...(All data are gone in RAM after shut off )
(But data in flash does not die after shutting the device off, that's what
i know)

 flash include data for booting, but the data must be loaded into RAM to
boot. So, after initializing RAM, CPU send kernel into RAM to proceed. (I
dont know why exactly, but it's the way that all coputers do.)