[Q] Location of bootloader (and code for Samsung download mode)

Hi guys,

Could anyone explain to me where the bootloader is located on a typical Android device? Does it recide on the SD card or is there a special storage area for it? I'm not talking about the boot image partition, but the actual bootloader (fastboot mode) and the code for the Samsung Download modes. Typically this would be located in the beginning of the harddrive on a PC but I don't think this is the case with Android. :)

I hope you Android gurus out there could enlighten me!

Thanks!