I have encountered several problems during these two weeks. Please help me!

I have encountered several problems during these two weeks. Please help me! -- Linux general technology-Linux technology and application information. For details, refer to the following section. Question 1. my motherboard has two sata interfaces, one optical drive and one hard drive. The hard drive is sda. What I want to ask is if I want to swap the hard drive lines with the optical drive lines, is the number corresponding to the hard disk sdc ??

Question 2. we know that the hard disk MBR can only contain information of four partitions (three primary partitions and one extended partition) due to limited space ), you can divide the extended partition into multiple logical partitions. My question is, why does the MBR space have limited space to load information about four partitions, and there is so much space to load information about logical partitions at the beginning of the extended partition? What are their principles?

Question 3: My linux version is ubuntu9.04 and the logout command is exit. However, after I enter exit under the root permission, the system only closes the current terminal window. What is the problem ??

Question 4: The book says that/etc/filesystems has a file system supported by linux, but I don't have this file in linux. What is the problem? Where did I go ??

Question 5: What is the major code of the hard disk ??

Question 6. we know that the Mount Start Menu is/etc/fstab. What is the difference between the menu and the former in/etc/mtab )?

Question 7: The following is an example of creating a virtual memory space:
Dd if =/dev/zero of =/temp/swap bs = 4 k count = 16382
Mkswap/temp/swap
Swapon/temp/swap
My question is: what is the meaning of each part of the file created in this way? Please explain it in detail. Thank you !!!!!!!!

Question 8: will the system prompt you to enter the password when you use sudo? Is this the root password?

Question 9.what are the similarities and differences between gzip compression and bzip2 ??

Question 10: when you use the locate command to search files, you must call a database to query information. The book says that/usr/bin/updatedb can be queried and changed. How can I operate ubuntu9.04,
I did not see any information.

Please give me some advice. I am very grateful !.