CMOS vs. BIOS

[marscheese]

Just wondering what the difference was between the two...can't seem to get a very good explanation from anyone. SO, I thought it might be a good move to turn to you guys.

Thanks ahead of time.

[blade]

For us computer users the bios is where we set the motherboard settings. Ram timings, v-core, etc..

We reset the Cmos when we need to set the bios to default settings after trying some extreme oc'ing. Or other troubles. That's about the only time we ever manually use cmos. It's when our system cannot boot, so we need to reset the cmos which in turn resets the bios.

This may not be what you're looking for but others may can give you a more technical answer, but heres the definition of cmos:

<i>CMOS (complementary metal-oxide semiconductor) is the semiconductor technology used in the transistors that are manufactured into most of today's computer microchips. Semiconductors are made of silicon and germanium, materials which "sort of" conduct electricity, but not enthusiastically. Areas of these materials that are "doped" by adding impurities become full-scale conductors of either extra electrons with a negative charge (N-type transistors) or of positive charge carriers (P-type transistors). In CMOS technology, both kinds of transistors are used in a complementary way to form a current gate that forms an effective means of electrical control. CMOS transistors use almost no power when not needed. As the current direction changes more rapidly, however, the transistors become hot. This characteristic tends to limit the speed at which microprocessors can operate. </i>

From http://whatis.techtarget.com/definition ... 60,00.html


Definition of Bios:

<i>BIOS (basic input/output system) is the program a personal computer's microprocessor uses to get the computer system started after you turn it on. It also manages data flow between the computer's operating system and attached devices such as the hard disk, video adapter, keyboard, mouse, and printer.
BIOS is an integral part of your computer and comes with it when you bring it home. (In contrast, the operating system can either be preinstalled by the manufacturer or vendor or installed by the user.) BIOS is a program that is made accessible to the microprocessor on an eraseable programmable read-only memory (EPROM) chip. When you turn on your computer, the microprocessor passes control to the BIOS program, which is always located at the same place on EPROM.

When BIOS boots up (starts up) your computer, it first determines whether all of the attachments are in place and operational and then it loads the operating system (or key parts of it) into your computer's random access memory (RAM) from your hard disk or diskette drive.

With BIOS, your operating system and its applications are freed from having to understand exact details (such as hardware addresses) about the attached input/output devices. When device details change, only the BIOS program needs to be changed. Sometimes this change can be made during your system setup. In any case, neither your operating system or any applications you use need to be changed.

Although BIOS is theoretically always the intermediary between the microprocessor and I/O device control information and data flow, in some cases, BIOS can arrange for data to flow directly to memory from devices (such as video cards) that require faster data flow to be effective. </i>

From http://searchwin2000.techtarget.com/sDe ... 14,00.html

[FlyingPenguin]

As simple as I can make it:

BIOS: Is the program that runs when you first power on the computer BEFORE it starts loading anything else (like the OS). It's a very small program that tells the computer how to run the POST checks, detect devices and assuing IRQs, and how to communicate with the hard drives. It includes a very simple loader program (called a bootstrap in the old days) to load the boot files off the hard drive, which then take over and loads the OS.

BIOS is called "Firmware". It's not stored in RAM, it's stored in ROM (Read only memory). The BIOS chip is the ROM where the BIOS is stored.

CMOS: CMOS is a type of RAM that the BIOS program uses to store volatile information (like the time and date, the settings from the BIOS menu, etc). CMOS ram has the unique ability to retain it's memory using VERY little current. CMOS uses so little current to retain it's memory that the small 3 volt lithium battery on the motherboard contains enough current to sustain that memory for years.

When you remove the CMOS battery (or short the CMOS reset jumper) you remove power from the CMOS memory which wipes the memory - clearing all the BIOS settings.

[marscheese]

alright, what Flying Penguin said makes a lot of sense to me, and sounds a little like what I've been hearing...BUT, why when you go into CMOS (by hitting delete when you're computer is starting up), does it say that you're in the CMOS setup? It sounds (by Flying Penguins definition) that BIOS loads everything before POST, and that the CMOS stores BIOS's information...so if CMOS stores information, why is it able to modify it also? Shouldn't this be BIOS's job?

[FlyingPenguin]

BIOS is the program that controls the most basic functions of the computer (BIOS = Basic Input/Output System)

CMOS is the memory that stores variables used by BIOS (the settings for all the items that you can set in the BIOS menu are stored in CMOS like whether the printer port is enabled, etc).

BIOS itself contains the program that runs the BIOS setup menu.

A lot of times you'll see the BIOS Setup menu referred to as the CMOS setup menu. Means the same thing.

CMOS does't modify anything - CMOS is just a type of memory (like DRAM, SRAM, etc). BIOS is the program that's running when you're in the BIOS setup menu and it stores all the BIOS settings in CMOS.