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Hi all
I hope I can get this cleared up, we had a bit of an argument last night at my A+ course. Unfortunately the teacher is less than...coherant shall we say.
What is BIOS and CMOS?
Are they classed as Hardware or Software?
What functions do they perform?
ROM and RAM...which is which and what do data do each store?
Thanks for any inputs.
Hong
A+ certifactaion is way overated.
Yes, some may agree but back to the original question...
What is BIOS?
What is CMOS?
They are classed as Firmware (a combination of Hardware and Software)
so basically they do the same thing, just that the Cmos uses less energy and that makes them attractive for Laptops?:(
I gotta get my head straight, I have so much info on BIOS and CMOS the last few days I am gettin into a right muddle...
Urgh.
Right. My understanding of this in the first place was:
The BIOS is the name of the ROM Chip that holds all the data about how to start the computer up, and perform POST, etc.
And the CMOS was a software located on the BIOS Chip that enabled a UI for one to change the BIOS settings, ie like time, date, other settings.
I'm pretty sure I am wrong on that.
Now, I have been led to believe BIOS and CMOS are two different chips.
HELP!
Hong
The BIOS is held in the CMOS chip and the CMOS chip receives power from the CMOS battery.
This could turn out to be a usefull thread for many people perhaps. You're not alone in you confusion hongman.
So in that case, is the CMOS chip nothing more than a container for the BIOS?Quote:
The BIOS is held in the CMOS chip and the CMOS chip receives power from the CMOS battery.
Thank you!! ;)Quote:
This could turn out to be a usefull thread for many people perhaps. You're not alone in you confusion hongman.
Hong
As far as I know, yes.Quote:
Originally posted by hongman
So in that case, is the CMOS chip nothing more than a container for the BIOS?
What is BIOS? (Mini-FAQ)
Quote:
To perform its tasks, the BIOS need to know various parameters (hardware configuration). These are permanently saved in a little piece (64 bytes) of CMOS RAM (short: CMOS). The CMOS power is supplied by a little battery, so its contents will not be lost after the PC is turned off. Therefore, there is a battery and a small RAM memory on board, which never (should...) lose its information. The memory was in earlier times a part of the clock chip, now it's part of such a highly Integrated Circuit (IC). CMOS is the name of a technology which needs very low power so the computer's battery is not too much in use.
Bios code [ Firmware not software] is retained on a CMOS [Complementary Metal Oxide Semiconductor] ram chipQuote:
And the CMOS was a software located on the BIOS Chip that enabled a UI for one to change the BIOS settings, ie like time, date, other settings.
EDIT:
BIOS as firmware
Quote:
BIOS is sometimes called firmware because it is an integral part of the system hardware. Before 1990 or so BIOSs were held on ROM chips that could not be altered. As their complexity and the need for updates grew, BIOS firmware is stored on EEPROM or flash memory devices that can be upgraded by the user. However, a failure in updating a BIOS can render a computer unusable. To avoid BIOS corruption, some new motherboards have a backup BIOS.
A computer system may contain several BIOS firmware chips. In addition to the boot BIOS, which contains code to access fundamental hardware components such as the keyboard or the floppy drive, plug-in adapter cards such as SCSI or USB hard disk adapters or video boards may include their own BIOS, complementing or replacing the system BIOS code for the given component.
Quote:
While the name BIOS is an acronym, it is also a play on the Greek word βιος (bios) life.
Thanks 10. That has made it a little clearer but I am going to have to read it a few times to grain it into my head... I have too much false info placed in my head.
Its like trying to unlearn an old habit...
So is the tutor doing this as a form of torture or do they actually not know the correct answer? :D
Both :mad: :(
You have hardware and you have software. Now how are you going to get them to work together. You have to have an interface function to accomplish this. In the case of the PCs we are talking about a function is fullfilled by the Basic Input/Output System whose acronym is BIOS. This is software stored on a ROM Chip on the Motherboard in this day and age. Now if the ROM chip is on the MOBO it will lose its info when the computer is powered down. So we have a Complimentery Metal Oxide Semiconductor which will store the info the Bios needs. It does this by depending on a CMOS battery to keep this small amount of memory powered up.
If your computer is off and you turn it on the CMOS memory which is holding the date, time, and system set up parameters will transfer info to the Bios allowing it to check your hardware and if all is well, the BIOS then has finished its job and gives control of your computer to your operating system software.
There is more if anyone wants to jump in. This is the basic start on all pcs.
Hope this helps abit in understanding the concepts. :) :)
Ok, so are the BIOS and CMOS collectively known as Firmware, or are they both classed as Firmware on their own of one hardware, one software thus collectively Firmware?
Hope that makes sense...:confused:
Hong
From Upgrading and Repairing PC's by Scott Mueller:
Quote:
BIOS and CMOS RAM
Some people confuse BIOS with the CMOS RAM in a system. This confusion is aided by the fact that the Setup program
in the BIOS is used to set and store the configuration settings in the CMOS RAM. They are, in fact, two totally separate
components.
The BIOS on the motherboard is stored in a fixed ROM chip. Also on the motherboard is a chip called the RTC/NVRAM
chip, which stands for real-time clock/nonvolatile memory. This is actually a digital clock chip with a few extra bytes of
memory thrown in.
The first one ever used in a PC was the Motorola MC146818 chip, which had 64 bytes of storage, of which 10 bytes
were dedicated to the clock function. Although it is called nonvolatile, it is actually volatile, meaning that without power,
the time/date settings and the data in the RAM portion will, in fact, be erased. It is called nonvolatile because it is
designed using complementary metal-oxide semiconductor (CMOS) technology, which results in a chip that runs on very
little power. A battery in the system, rather than the AC wall current, provides that power. This is also why most people
incorrectly call this chip the CMOS RAM chip; although not technically accurate, that is easier to say than the
RTC/NVRAM chip. Most RTC/NVRAM chips run on as little as one microamp (millionth of an amp), so they use very little
battery power to run. Most last five years before the lithium battery runs out and the information stored gets erased. Some
systems use a Dallas Semiconductor RTC/NVRAM chip (such as the DS12885 and DS12887) that also contain the
battery.
When you enter your BIOS Setup, configure your hard disk parameters or other BIOS Setup settings and save them, these
settings are written to the storage area in the RTC/NVRAM (otherwise called CMOS RAM) chip. Every time your system
boots up, it reads the parameters stored in the CMOS RAM chip to determine how the system should be configured. A
relationship exists between the BIOS and CMOS RAM, but they are two distinctly different parts of the system.
ROM... Read Only Memory ... works like a CDR, once you write it, there you go. Non-volatile, no power requirements to hold it's data.
RAM... Random Access Memory ... this is the read/write stuff we all want more of! Data is accessed in a random manner, can grab any portion of memory unconditionally. Volatile, needs power... once the power's gone so is any information stored on it.
CMOS... The chip that holds your BIOS information. Generally hardwired to your motherboard, but can be of the removable variety.
BIOS... Basic I/O information. Low level instructions used in the boot process.
POST... Power On Self Test. Uses the BIOS program to check that all is good, makes sure your motherboard is talking properly.
Firmware is actually a combination of a ROM chip and software that is written onto it. It does not change unless done so externally by you the user.
To go one step further on BIOS. BIOS is another word for device drivers.
And one more step. The BIOS on your Rom Chip is just one part of overall BIOS. Normally this can be broken into four parts; hardware, Rom Bios and device drivers, operating system, and any application program.
Each PC unless of the same make and series can be abit different in their hardware so the BIOS will have to be adjusted which when all is said and done allows an operating system to work with different manufacturers PCs. The application program once the operating system is up is a straight thru interface usually.
My suggestion to you, Hong, is to get each piece of the puzzle firmly in place and then just add to it.
Hey we need some more members inputs into this discussion. If I make a mistake it needs to be corrected. And for those of you others that have a question on some part of this jump on in. The fastest way to learn is ask questions and the next which was hard for me in the beginning was to read/listen, because if that is not done there will be no learning and understanding in your minds.
This is a good thread Hong started. Much can come from it for everyone. :)
Thanks Greengoose.
I think this is a widely debated subject, a lot of people (inc me) think they know what it is, but when asked they actually struggle to give a straight and definate answer. This has been the case of all the people I have asked (non-Vdr).
Ok, to summarize:
BIOS (Basic Input Output System): Is a ROM (Read Only Memory) chip (thats the hardware part) that holds the hardware parameter's (thats the software part of it) needed for the system to start up, and POST (Power On Self Test).
Can anyone confirm#?
I believe you've got it. But as I said that is only part of it.
If DrMDJ comes in on the Train we might see some more discourse in addition to what has already been said. :D :D
And then we have "lurkers". What say you, silent experts?
There's some still sleeping on the other side of the world.
Always wait at least 24 hours for replies because of the time zones.
Thanks, looks like that bit has sunk in.
Yes, I'll wait for replies.
Then, when this has all been cleared up this thread is getting printed and laminated and framed and....hung on my wall!!! ;)
Anyone care to tackle CMOS, in the manner I did above? I dont feel up to it yet, but if anyone does post please, dont assume ANYTHING!
It takes just one thing to not make sense, and the whole lot gets jumbled up.
Thanks to all
Hong
The more I read that, the less correct it becomes. :DQuote:
BIOS (Basic Input Output System): Is a ROM (Read Only Memory) chip (thats the hardware part) that holds the hardware parameter's (thats the software part of it) needed for the system to start up, and POST (Power On Self Test).
BIOS is the collection of routines (software) that enables the hardware to initialize (which includes POSTing) and be able to communicate with the operating system. BIOS isolates the fundamental nature of the hardware from the operating system by providing a consistent set of routines that, while they may vary internally from one computer to the next, require and return a uniform set of values and perform identical end-result operations. While the BIOS has to know how to interpret the bits returned by the interface chips, the operating system is able to ask "tell me what key was pressed".
The BIOS of an IBM compatible personal computer is held in a non-volatile form of memory (EEPROM -- electronically erasable/programmable read only memory), with more readily changeable parameters held in a battery-backed form of memory (CMOS RAM). BIOS is considered firmware because of its relationship to the overall system. While today it is alterable by the end user, the BIOS routines were originally in ROM memory formed into readable bytes at the time the silicon chip was manufactured -- it was software held firmly -- firmware.
BIOS sits between the hardware and the operating system, the operating system sits between the BIOS and the application program, the application program sits between the operating system and the user. "the leg bone's connected to the, knee bone..."
Think of EEPROM as a CD-RW, where the bytes written to it can be deliberately changed, but then doesn't require anything external in order to retain those byte values.
CMOS was originally just an acronym for one way to create semiconductors. It has been bastardized by mis-use to now also mean the data values stored for use by the BIOS routines, or the location of that data.
And don't get too tied up in the physical properties of all of this, because that changes with time. You can actually have everything, including the microprocessor, on a single silicon chip. There's nothing special about how it's done on your typical personal computer, they are just basic building blocks.
And that's my two cents worth. :cool:
Thanks Prouton, obviously my explanation was very basic :p
As I have been saying all today, the more I read the more confused I am getting.
I need to wake up tomorrow with a fresh mind, and then read everythng over again, then I'll grasp it. :rolleyes: :D
However saying that, you explanation of the BIOS is very detailed, exactly what I was looking for. After all, if I have to re-teach myself this I may as well know the intricates, not just the surface ay ;)
I cannot stress how much I appreciate your responses, means a great deal to me (and my passing the A+ of course!)
Hong
Ah, I see this thread has picked up some steam since I last saw it this morning. :D I'll just throw a quick couple of cents in...
But if the implication is that the OS goes through or uses the bios (bios routines) to talk to the hardware then that depends on the OS. With modern/current OSes once the very earliest phases of the the OS initiation process have been gone through, from that point on communication with the hardware by and large completely bypasses the bios (bios routines). The communication is directly between the OS (even app in some cases) and the hardware.Quote:
BIOS sits between the hardware and the operating system
The role of the bios has been reduced greatly. In today's systems it's primary role is simply that of a kickstarter for the system and OS.
Keep it going folks:)
Fact is that doing away with the BIOS/CMOS as we know it today is fast approaching. But until it gets here, the BIOS once the computer is booted up, has basically nothing to do until you boot the system the next time. And the newer the OS and computer the less tie there is.
So once the startup routine is passed to the OS, that is about it.
Hope you don't mind me quoting Bigelow's :D
In general the BIOS contains three sections the power on self test [POST],the CMOS set up routine and the system services routine.The particular section of the BIOS code that is executed depends on the computers state and its activities at any given moment.
POST: Performs a low level diagnostic and reliability test of the main processing components including ROM programs and system RAM.It tests the CPU,initialises the motherboards chip set ,checks the 128 bytes [or more ] of CMOS for system configuration data and set up an index of interrupt vectors for the CPU from 0000h to 02FFh.POST then sets up a BIOS stack area from 0300h to 03FFh,loads the BIOS data area [BDA] in low memory 0400h,detects any optional equipment [adaptor]BIOS RAMs] in the system,and proceeds to boot the OS from an available disk.
CMOS Setup routine:The hardware configuration for a system is held in a small amount of very low power CMOS RAM .........
At boot time the POST gathers information about the systems hardware and compares it with the settings in the CMOS RAM.If the hardware matches the system is deemed to be operational and the boot process continues.Otherwise the boot process halts and the system set-up error appears.
System services routingAlso reffered to as BIOS services are a set of individual functions that form the layer between the hardware and the OS...................
Services are called through a use of interrupts .An interrupt basically causes a CPU to stop whatever it was working on and sends program control to another address in memory that starts a subroutine designed to specifically deal with that particular interrupt.When the interrupt handling routine is complete the CPUs state is restored and control is returned to where it left off............
Interrupts can be produced by three main sources:the CPU,a hardware condition and a software condition.
American mega trends[AMI] bios sequence:
1/Disable NMI [non maskable interuppt line] to CPU a failure suggests a problem with CMOS RAM
2/Power on delay : resets the soft and hard reset bits
3/Initialize chip set
4/Reset determination: reads reset bits in keyboard controller
5/BIOS ROM checksum: adding a factory pre-set value should equal 00h or show as defective.
6/Keyboard test
7/CMOS Shut-down check:
8/Controller disable: disables DMA and IRQ controller chips.
9/Disable video
10/Detect memory
11/PIT [programmable Interuppt timer]test
12/Check memory refresh
13/Check low address line
14/Check low 64KB RAM
15/Initialize support chips
16/Load INT [vector table
17/Check the keyboard controller
18/Video test
19/Load the BDA into conventional memory
20/Test memory below 1MB
21/Check DMA registers
22/Check the keyboard
23/Perform high level tests
24/Load OS.
BIOS PatcherQuote:
WHAT IS "BIOS Patcher"?
BIOS Patcher is a kind of software that can find and fix errors in your system BIOS (only AWARD BIOS for now) and also it can add or open new features, i.e. some features that your BIOS has but they are closed by manufacturer of your motherboard.
Thank you for the responses, its good to see them.
How much of the A+ is tested on BIOS/CMOS?
And that area of memory - the first 64KB... is it KiloBytes of just Bytes? I have head people using the two interchangeably and just want to triple check. ;)
104456, that adds a bit more to the depth of the subject. The bios setup steps shows just what a PC goes through to make sure everythung is in order so control can be handed off to the operating system. And it is within those steps that various error messages can pop up on the monitor. Lots of places for error messages.
I had not thought much about bios disappearing Train. What and how is it going to be replaced?
KiloBytes but modern bios chips can be in the 2MB range.Quote:
Originally posted by hongman
And that area of memory - the first 64KB... is it KiloBytes of just Bytes?
The BIOS Chip
Quote:
The capacity of BIOS chips is measured in Megabits (Mb). Most BIOS chips these days are 2Mb (256KB) in size. These higher capacity chips allow the manufacturer to offer more features than is possible with the smaller 1Mb chips.
Thank you for clearing that one up!!
I'm curious as well now that Greengoose mentions it...how will there be a future without BIOS's?
One thing I think needs to be made clear here. The bios and cmos memory area being talked about here in these definitions and such refer to the main or overall "system" bios and cmos (or nvram if you like) memory. As has been noted elsewhere, there can be (and are) other bioses in one's computer. And since "CMOS" is a particular process used to make semiconductors/ICs, the CMOS type memory used by (in conjunction with, as a storage place of certain information/settings for) the system bios is not the only place you'll find CMOS technology or memory in one's computer. Anyway...
Before I forget let me throw in one point here... The system bios (any bios for that matter) is code/instructions. The system bios, the bios chip, has no instruction execution capability of its own. It requires the/a cpu to execute the code it contains. So at initial power on the the cpu must be initialized successfully before any bios operations can take place. Without a functioning (at least to some extent) CPU the bios is just little more than a chip with cpu instructions sitting in it.
A couple changes/additions to the Bigelow info...
The inital initialization of the CPU and chipset is done prior to the POST (prior to the bios code even beginning). This has to be the case (again, since the bios is just code).
What Bigelow describes as the "P.O.S.T." function is quite overstated. That true POST sequence is a very quick and fairly basic inventory and test of certain hardware. Bigelow seems to have lumped all initialization and inventoring type functions performed by the bios under the POST category, when in fact the POST (sequence) is just one (the initial) part of a process that extends after the true POST has been done. It would be more accurate if Bigelow had called the function/heading "System Initialization" rather than "POST". The POST is part of the sequence of things done by the bios under that category of system initialization. But most of the things that happen from the time the bios code first starts executing until it finishes its job are not part of the POST though. Ya might say I'm being picky here, but...
And while I'm being picky (;)) let me pick on one other thing. The bios routines do not "proceeds to boot the OS from an available disk". The bios code "begins" (or tries to) the process of booting an OS. What the bios code actually does is go sequentially through the list of boot devices (that the user has specified, and which are stored in the cmos data area) one by one checking to see if there is viable boot code in the proper place, and then loading and passing execution control to the code in this boot record. In the case of, say, a hard drive this would be code in the Master Boot Record of the drive. And in the case of a hard drive this code would not be operating system boot code, but meerly code that would in turn try to locate, load and start execution of the actual OS boot code (in the partition/volume boot record). Like I said, I'm being picky but...
And finally, on the stuff about the bios sitting between the hardware and OS or other software... Not to beat a dead horse but again, with currrent/today's systems the role of the bios after it has initiated the boot process has been tremendously reduced. Once the system is running (so to speak) the bios routines are much less used or relied on, and largely out of the loop (and not in control).
OK, enough for now. Again, good thread!
It's not that there won't be bioses per se. But what will be (and has been) happening is that the code and functions performed by the code in the "system bios" will be offloaded. Instead of being centralized on one chip, it will be distributed more and more to other hardware components (chips, devices). For instance, instead of having the system bios handle all video related needs, you offload the code and functions to video card itself. Or, you resonsibility and handling of i/o operations between a disk drive and the OS and offload these to the OS code and hardware/firmware on the device. Just two quick examples.Quote:
how will there be a future without BIOS's?
There are actually valid reasons and benefits why the "system bios" can not and should not remain the "master and commander" it once was. Given the increasing demands, complexities and capabilities of the technology (hardware and software) it has become and is becoming less and less efficient and even practical to have the system bios be and do what it once did.
Wow.
I was wondering when you were going to make your mark on this thread ;)
Ok so the BIOS Chip holds code for system initialization, that the CPU will execute, and the CMOS holds other settings to do with booting, like boot sequence, motherboard devices, etc.
Is that correct, in a less-in-depth sense? I need to grasp this bit before I can concentrate on the individual roles of everything else.
DR, so accoring to what you were saying, the CPU actually initializes itself (to run the BIOS code)? I was under the understanding that the BIOS initialized the CPU, but then again what do I know :p
Thanks ppl
HOng
PS After this thread I best be an expert on this!!:D
Interesting............so is this code not part of the operating system per se be it an initiation code to get the OS running or is it an entity unto itself i.e a bootstrap if so where does it originate from ?Quote:
In the case of, say, a hard drive this would be code in the Master Boot Record of the drive. And in the case of a hard drive this code would not be operating system boot code, but meerly code that would in turn try to locate, load and start execution of the actual OS boot code (in the partition/volume boot record)
No. What actually happens is that when power to the system is turned on, the power supply comes up and does some self tests (and makes sure power levels are up to snuff). During this time the motherboard chipset has sent a signal to the cpu to put it in a reset state (on, but kind of in a holding pattern so to speak). Then when the PS is satisfied things are ok with it it sends a sinal (what's called the Power Good Signal) to the CPU that tells it to got ahead. Then at this point the CPU goes out to a predefined and specific memory location (as per convention) on the BIOS' rom and fetches it's first instruction to execute (which is nothing more than an instruction that causes a jump/branch to another memory location where the true beginning of the bios startup code is). And things progress from there.Quote:
the CPU actually initializes itself (to run the BIOS code)?
Yes, the CMOS holds settings, some hardware configuration info (not all) and the system time/date. The bios (chip) does hold the code for system initialization (speaking broadly, and which includes the POST functions, startup screen functions, etc, etc) and inventorying a lot of the hardware, plus:Quote:
Ok so the BIOS Chip holds code for system initialization, that the CPU will execute, and the CMOS holds other settings to do with booting, like boot sequence, motherboard devices, etc
- The code used to provide the interface to update the cmos settings.
- The various low level routines/functions (system services as referred to in 104456's post) that others have referred to, and which can but may or may not be used by the OS, programs, etc.
And it can and often does contain code that:
- Enables a bad system bios flash to be recovered from (often referred to as "boot block" code.
- Enables a system bios system bios flash to be initiated.
Thanks DR.
Feels like I am finally getting somewhere now. Under the generalisation i posted earlier, I can now use that to build upon the more 'complicated' things mentioned in this thread.
Thank you all!!
Hong
104456,
"Bootstrap" code is probably a decent description. Again, in the case of a hard drive (things differ with other bootable devices), the code in the MBR, the code the bios loads and kicks off, is not specific to an OS per se. It is generic, and functions to then find and load OS boot code in another boot record in a partition. Now of course it "could be" anything viable ya wanted to put in there.
When one is using, say, a disk overlay, the disk overlay puts its code in to the MBR (so it can hook in to things right off the bat). Same with something like third party "boot loaders".
When you do, say, and FDISK /MBR what it is doing is putting a generic set of boot code in the MBR (that then goes off and does what's described when run). It is not specific to say Win95 or WinME or WinXP. Their specific boot code is loaded in to partition boot sectors/records (in the base case in the active primary partition). In the case of something like Win9x/ME (even dos) the SYS command is one way to update this code and put in place an OS boot record. The MBR code kicks off this boot code.
Through this thread I have noticed a few bits and pieces, one of which is mentioned above. My question is, why does it have to fetch one bit of code which then justs points it into another bit of code? Point being, why doesnt it just go straight to the 'true' beginning?Quote:
fetches it's first instruction to execute (which is nothing more than an instruction that causes a jump/branch to another memory location where the true beginning of the bios startup code is)