[Q] Some questions about Android Recovery Mode topic

Recently I was studying android recovery mode, and I have some questions. Anyone knows the answer? Thanks very much.
1. Can recovery flash bootloader?
From this link====>http://forum.xda-developers.com/show....php?t=2321310, I think it can do that. But I'm not sure.
2. Can recovery flash recovery partition itself?
I think it can not do this. Not confirm that.
3. We know in update.zip, boot.img is corresponding boot partition, but why system is a folder, not system.img? There is a system partition also.
4. While OTA upgrade system, why the update package downloaded under /cache path? Can we change it to sdcard?
5. Most important, what exactly update-script do things under recovery mode? How the command executed?

BTW, there are other questions, but not related to Recovery Mode.
1. How can I see the flash partitions? I know to use the command cat /proc/mtd, but as Samsung, it use emmc flash, while I type that command, no results printed. How to see?
2. About userdata partition, we know that when first run android OS, system will copy files from /system to /data, but does it do it every time that we turn on the phone or just do it once after the first booting after we update our system?