|The CMOS data is a small part of the BIOS data , but it's not all of it.|
The BIOS chip is a combo chip, not just the CMOS part - it has both non-volatile and volatile data. There is non-volatile data, the majority of the data, that does not need power to retain it, in the (e.g. 4 mbyte) EEPROM part of the chip (Electrically Erasable Programmable Read Only Memory) and volatile data in the tiny (e.g. 64 byte) CMOS part of the chip that requires at least a minimal voltage and a minimal current from a battery, rechargeable or not rechargeable, to retain at least the current Time and Date, and any other User set settings that are not defaults, when the computer is not running or when all other power to the mboard has been removed..
When you clear the CMOS, e.g. by moving a jumper then moving it back on a desktop mboard, or when you remove the battery for a short time then re-install it, you are only clearing the data for the current Time and Date, and any User set settings that are not defaults.
Some of what you see in the bios Setup is determined automatically by the bios for particular ram and cpu the mboard has installed in it and the drives connected to it every time you boot the computer - it does not require a battery and the user can't change the settings of most of that data.
The first thing the BIOS does is check the information stored in a tiny (64 bytes) amount of RAM located on a complementary metal oxide semiconductor (CMOS) chip. The CMOS Setup provides detailed information particular to your system and can be altered as your system changes. The BIOS uses this information to modify or supplement its default programming as needed.
Most of what you see in Setup is on the EEPROM part of the bios chip. Most of the data on the EEPROM part of the chip is not visible in Setup at all.
The EEPROM part of the chip is what you change data on when you flash the bios to a different version, although a small part of that data is for the Boot Block portion, which is not normally changed when you update or downgrade the bios version.
In the case of modern laptops and netbooks (about a dozen years old or newer) , they have a second chip that user data is stored on, including the password info, that cannot be cleared by removing the power to the chip. Clearing the CMOS or removing the CMOS battery then re-installing it does NOT clear the user data on that second chip.