December 1, 2013

Difference and Relationship between BIOS and CMOS

Because of the tight relationship between BIOS and CMOS, they are recognized as the same program at most of time, just their name are different. Actually, they are different two things which are related with each other. So what is BIOS, CMOS? And what are the difference and relationship between BIOS and CMOS?

One: Concept Difference between BIOS and CMOS 

CMOS is Complementary Metal Oxide Semiconductor. Because of its characteristics of the read and write, CMOS is used to save data about computer parameters set in BIOS program on motherboard. So its main function is save data.

BIOS is one EPROM or EEPROM chip on computer motherboard. BIOS Setup program is stored in it, which saves important system information and system parameter.  

Actually, BIOS is Basic Input-Output system in microcomputer, whose content is integrated in a chip on microcomputer motherboard. The most important input and output program of microcomputer, system information setup, POST and bootstrap program are saved there.  

Two: Main Function Difference between BIOS and CMOS 

CMOS main function:

1. Quick Power On Self - Test
When computer is starting, motherboard will take a series check and test on systems and peripheral devices. If you set it Enabled, computer startup speed will improve.

2. Boot Up Floppy - Seek
When computer is starting, BIOS will check whether Floppy is available. If you choose Enabled, when BIOS find no floppy, it will prompt you that is wrong.

3. Boot Up NumLock – Status
Generally, the small keyboard in the right side of big keyboard is used as number keys default. If it is necessary, you can set it OFF, and small keyboard would become direction keys.

4. Security Option
There are two options between Security Option, if you set it as “Setup”, no password is needed to login computer, but password is needed to enter CMOS, which is set before. And only supervisor password could change parameters for CMOS. If you set it as “System”, you will need computer logon password, and only supervisor password could modify CMOS.

How to set password in CMOS?
Two kinds of password settings are provided in CMOS for user, Supervisor/User Password). Follow the below:
  1. Choose Supervisor Password on main interface, press Enter and “Enter Password:” appears.
  2. The length of password could not be longer than 8 characters. When you finish typing it, press Enter.
  3. Confirm Password now. Type password you just input and press Enter to make sure.
Tips: When you set Security Option as “System”, you can type one of Supervisor password or User password to access Windows computer. And please remember back to main interface and press F10 and Enter to save these changes.

BIOS main function

1. BIOS Interrupt Service Program
It is a programmable interface between software and hardware in microcomputer system. It makes application software functions appropriate link up to microcomputer hardware. The management on floppy, disk, CD-ROM, keyboard, displayer is based on BIOS system interrupt service program. And computer operator could call this program directly by accessing break point, such as INT5 and INT13 etc.

2. BIOS System Setup Program
This program is used to set parameters for CMOSRAM. Just press boot key when you start computer and you will enter this program. And this process to set parameters for CMOS is also called BIOS settings.

3. Electricity Self-Inspection Programs on the POST
When microcomputer is connected with power, POST will check equipment inside system. Once there is problem in check process, system prompt message will pops up for computer user.

4. BIOS System Bootstrap Program
After system POST completes, ROMBIOS will search for soft and hard disk drive, CD-ROM, Network Server according to setup sequence saved in CMOS settings. Read operational system boot record and give control privilege to boot record. Boot record will let system boot successfully.

Relationship between BIOS and CMOS

From the above introduction, you can see BIOS and CMOS is inseparable. We have to set up CMOS through BIOS setup program, and BIOS information is stored in CMOS. So at most of time, we usually called CMOS setting as BIOS setting. Both of them are settings on computer hard ware. And setting parameters are saved in CMOS chip. 

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