i know bios is a silicon chip, here is my question:
1. dose bios can execute codes, like copy some bytes from rom to ram;
2. how does bios address ram and rom, how does it know where ram and rom is;
3. when power on, why bios knows what to do, and how does it do it.
help!!!!!
thanks advance.
This is a head-banger :bgrin:
Sorry xiahan - just my sense of humor :biggrin:
BIOS - Basic Input Output System
Bios is essentially the startup code for the motherboard - to get it working.
When you power-up (or reset) your PC, the processor (CPU) has to start somewhere, as at this stage it is 'clueless'
The BIOS ... sets up a very 'basic' system for the next stage of the BOOT process
Times have changed, but generally the next stage is reading the CMOS which holds hardware configuration info and other details.
From this BIOS now starts loading boot information from hard disk, or by other means... then finally your Operating System (windoze or other)
BIOS is an executable in the most lowest level of the PC and is the realm of hardware and system programmers.
If you don't know the hardware like the back of your hand - do not touch the BIOS ;)
Ram/Rom
Every motherboard is designed by a manufacturer. In the design there are different types of chips which control different aspects of the computer.
Each of these chips have datasheets a gazillion pages long, describing how to correctly program them - This is what the manufacturers BIOS programmer does.
These chips are Memory management, communications, on-board video...ect.
Every manufacturers motherboard (mobo) is slightly different, but functionally the same through BIOS
BIOS is the mobo's hardware interface/connection for the Operating System (Windoze).
:t
hi K_F, i see my post again,really some kind of twisted,hah hah!
but the time i write the post i was just follow the way the sites on the Internet explaining it.
dose u mean the CMOS contains the specific info of the mobo whitch it atached ,so the cpu can has no knowledge of the hardware , it just execute instructions.
when an intel x86 processor starts up - or when it is reset - it begins executing at a fixed address
the BIOS ROM (or flash) is located at that address and contains code to get things going
beyond that, the primary function of BIOS is to provide a standardized interface to the disk operating system
that is to say that it provides a layer of isolation between the hardware and the OS
Quote1. dose bios can execute codes, like copy some bytes from rom to ram
the bios does execute code and does initialize RAM
Quote2. how does bios address ram and rom, how does it know where ram and rom is
the memory map for intel compatible PC's is more-or-less standardized
some of the standardization came from intel
some came from IBM
some comes from the different companies that have written BIOS's over time
Quote3. when power on, why bios knows what to do, and how does it do it
refer to the intel manuals
it starts out at a fixed address and executes the code at that address
as i recall, most of the registers are initially set to 0, except EDX and EIP
about the memory mapping,the BIOS ROM must have a address,to accelerate speed,the codes insides rom is copied to physical memory and then the addree of the BIOS ROM is redirect to the address in the physical memory,is that true,any docs will be preciated.
I have not checked any recent systems, but at one time there was a common BIOS option to "shadow" the system BIOS (and IIRC also the VGA BIOS) in memory, allowing the BIOS code to execute from there. I never investigated this, but I would guess that the address "redirection" was implemented by reprogramming the chipset address decoders. And I also recall an option to cache the BIOS, but I never investigated this either. In any case, with a PM OS that does not use the BIOS once it's up and running these options provide essentially no benefit, so they may have been eliminated in recent systems.
now i have a more clear view of the bios,thanks guys!
i think the shadow stuff basically copied the ROM into RAM and vectored the interrupts to appropriate addresses
a good section of the ROM is startup code, however
this is particularly true on newer systems, as the hardware requires a lot more initialization
you can get the intel manuals here...
http://www.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html (http://www.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html)
this website has a lot of BIOS-related information...
http://www.bioscentral.com/ (http://www.bioscentral.com/)
back in the day, Award and Phoenix were 2 companies that wrote generic BIOS
i understand they have now merged as 1 company and probably write for several manufacturers
AMI was another one that wrote BIOS
you can google those names and find more info
Hi,
I think MichaelW was correct about the shadowing of
the BIOS and VGA BIOS. The code was copied to RAM
and then remapped that RAM to the ROM address space.
This was to speed things up for DOS programs and maybe
early versions of Windows (or the like).
Most protected mode operating systems do not use
the BIOS, except in a "compatibility" mode for problematic
systems. Presumably now an obsolete mode. For example,
OS/2 would normally use protected mode code to access
the hard drive, but some systems did not work and forced
the use of a BIOS based driver for the "hard drive". Usually
something emulating a hard drive, or an oddball really
old drive. Using the BIOS to access anything in a PM OS
is/was a horrible performance hit. And of no concern with
modern systems. Modern probably meaning later than
the 486.
HTH,
Steve N.
Basic Input Output System check hardware devices, in a process called POST (power on self test), like recognize ammount of memory, hard drivers and others devices...
The code (read code and/or data) inside bios are called firmware. So, bios offers a setup program to us configure devices on the motherboard.
The firmware offers too some interruptions, so, you can use bios code to reach some facilities while coding (using 'int' instruction).
When you wakeup you computer, bios get the control, check everything, if find some problems, it send a speaker sound (beeps), if not, it access the code on specific offset, on configured boot device, and that will wakeup the O.S.
The batery (cmos) hold your saved configuration, and if you like to reset that information, remove the batery and generate a short-circuit on specifc jumper (to discharge the capacitor).
Bios know a valid boot code by searching by a signature (55aah, or 0aa55h, I forgot), generaly on the first sector of that device.
One day, i was updating 5 same computer bios (same motherboard), and on the half of write process to bios, blackout ocurred. After, I was able to put computer on, but bios code does not work, appears to me like a standby mode. So, how can I update bios using an image inside floppy if I cannot access floppy?
So, I removed that chip (integrated circuit), put a good one (removed from other motherboard) on that motherboard, turn computer on, read their code to update, and before write, with much patience and carefully to not create a short-circuit, I removed the good bios chip, put the damaged (firmware) one, and after started the write process. I was able to restore the damaged bios code. This was my last choice, and worked.
So, if I was able to update that internally bios code, we can create functions too and insert in that bios, like let's supose, optimized strlen function, and access then using interruptions or probably other ways. Not the best place to put that function, but... . From ms-dos times, I remember one debug program that offers you an easy way to overwrite specific memory places (like video rom bios). In today days, I remember see some discussions on vmware board about bios code and testing.
Old bios have only a rom part, new ones offers you a writeable part.
hi, eiro!
you are very familiar with the motherboard, can you explain more about the phrase
Quote
So, I removed that chip (integrated circuit), put a good one (removed from other motherboard) on that motherboard, turn computer on, read their code to update, and before write, with much patience and carefully to not create a short-circuit, I removed the good bios chip, put the damaged (firmware) one, and after started the write process. I was able to restore the damaged bios code. This was my last choice, and worked.
seems like u removed the bios chip, and when u put on a good one, u
Quote
read their code to update
read whos code? the code inside rom?update what?
Quote
with much patience and carefully to not create a short-circuit, I removed the good bios chip,
you replace the bios chip while the computor is on?
Quote
I was able to restore the damaged bios code.
can firmware be damaged? if so, how can you restore?
sorry for so many qustion mark, :biggrin:
maybe my question is very silly, please forgive me.
heh, the BIOS/Firmware can always be damaged, when u do sth with it... so best practice, FIRST do a backup copy/dump, while being able to RESTORE it in case of an eventual failure, mate!
each firmware give all you need to update your bios.
Be sure to find the good , this could take a certain time (many differents CPU).
Dowload it,with it you have a prog who made a backup of your old bios.
To be sure not to do a mistake,run msconfig.
Look the tools in it,run them and you have the answer.
Hello Sir xiahan;
Inside your motherboard cd-rom, have some utilities, like drivers to specific O.S. and an image of your bios, and an utility to you be able to update bios code (the code is stored inside the chip, firmware).
So you can update the code inside that chip. When I was updating that code, occurred a fail on source suplly. So, bios code cannot take on, like when you turn on your computer and press "del" or "f1" key, the code inside that chip was corrupted, so no response.
When you are updating bios code, the program ("afudos" to asus, forgot others) ask to you if you like to save the image inside bios as an file, and I saved it to floppy. When the program asked me to press a key to write the saved image (floppy) inside bios, I removed bios chip with computer on, put a fault on that place, and pressed a key to start writing the code to that chip. You can see this process like clonning a floppy disk, you need remove the original one and put other disk to write the image on that.
Some programs today permit you to update bios code while inside windows, but I have done that while inside ms-dos.
If I do not have other same bios chip to that motherboard, so the solution is remove that chip and give that with image to an eletronic person, he probably have a writer (flashrom,eprom,..) to restore the code inside that chip.
I'm not updated with new technologies; I have read that you can export/import and share your overclock settings with others, mouse support inside bios setup, games inside bios, ... . My last reading was about uefi that is new to me.
hi,mineiro,the good bios's code is shadowed into ram so it can run without bios chip present on the motherboard, and based on the same point, the bios code can be updated is possible.
yes Sir xiahan, the code was copied from bios chip to ram memory, but, I do not think that copying the ram contents back to bios will work 100%, I have read that some bios uncompress code to ram, instead of just copy their contents to ram.
After the code is stored on ram, the rom code is disabled, and ram code is used in their places.
what used to be a bios "rom" is more than likely a "flash memory"
a type of rom that is re-writable
i have never heard of it being "uncompressed" into ram
it is likely that much of the bios code is excluded when running from memory, however
there is a lot of device init and "post" (power-on self test) code that is not required after boot has completed
Quote from: dedndave on October 16, 2012, 10:27:56 AM
what used to be a bios "rom" is more than likely a "flash memory"
a type of rom that is re-writable
i have never heard of it being "uncompressed" into ram
it is likely that much of the bios code is excluded when running from memory, however
there is a lot of device init and "post" (power-on self test) code that is not required after boot has completed
In bios settings when it mentions "Shadow BIOS ROM" it is referring to certain ROM content being loaded into memory for faster access. In many bios configurations you can turn this on or off, for both the system and video bios. Not everything in the bios is shadowed this way.
i see those options less on newer machines
they might have been popular options in the days of win95 and win98
but the newer OS's probably work better without them
in fact, i seem to recall reading that they don't work with newer OS's
Dave,
Quotein fact, i seem to recall reading that they don't work with newer OS's
do you mean that the new OS use some methods to bypass the bios interrupt routine, like the OS not use the int 13 to visit hard drive,but use some workarounds.
i can't really answer that
i have an old machine that i haven't fired up for a long time :P
it's a 225 MHz P3
it has the options in BIOS setup to shadow either BIOS or video ROM
but, as i recall, it is better if you do not use those options
and let the OS handle it - which, i am guessing, takes care of it
it's likely that much of the original code for, say, INT 10h, is handled by the OS
it may buffer things like the character sets
and let the video ROM handle a few functions like mode changes
then - the OS code takes care of most of the rest of INT 10h services
Quote from: xiahan on October 18, 2012, 03:03:32 AM
do you mean that the new OS use some methods to bypass the bios interrupt routine, like the OS not use the int 13 to visit hard drive,but use some workarounds.
The BIOS was designed to support real mode operating systems, so virtually everything it provided consisted of real-mode code. For an OS that runs in protected mode using the real-mode BIOS I/O services and hardware interrupt handling would be cumbersome and inefficient, at best. So the decision was made to take full control of the system after the BIOS had booted the OS, bypassing the BIOS completely.
Newer operating systems may us interrupts at some underlying level, but the subset of the bios code still in use is not the same subset that was being shadowed to begin with. So it makes perfect sense today to turn it off and use something like DosBox for older apps. The only thing shadowed, above the base 640k of memory, was basic real mode device drivers. This could also include legacy USB support. Unless you have a fairly narrow set of requirements to use some legacy devices shadowing is not generally useful today.
all right, guys, now the bios code make more sense to me.