The Bios = BASIC IN OUT SYSTEM is the main code of of the Motherboard to start the computer after the power has been applied.
The Bios will be reset by the Real Time Clock or RTC and then it will test itself after that the first 256kb of RAM, will test the CPU and also IO (IN OUT) then also the VGA (Video Graphics Adapter) then it will test Keyboard Controller and many other things before it loads the BOOTSTRAP , which is a small program code ,this giving control to the Operating system .
There are many different BIOS's out on the marked and may the most well known are AWARD, AMI and PHOENIX .
The bios program is a small about 128 KB code which is compressed and which will be uncompressed as soon the computer has been started up, for Computers before of mid year 1999, after this many Motherboard and Bios Manufacturer changed to 256Kb BIOS's which will include features as knowing when a false CPU timing was applied the resetting itself to default settings. Then also there now it is possible to change the FSB FRONT SIDE BUS frequencncy from within the Bios same as Bus Core and CPU voltage and many other things.
To find out what kind of Motherboard is build in to the computer there are several ways to determine this. For AWARD BIOS's please click on this link then the 6th and 7th number will tell the manufacturer which can be looked up on several databases. Those Databases will be placed very soon on this website .
There are also several utilities to download form the bios manufacturers to determine the Bios.
Bios Post Codes
Description Turn off OEM (Original Equipment Manufacturer) specific cache ,shadow
1. Initialize EISA registers (EIAS BIOS only)
2. Initialize all the standard devices with default values .Standard devices include
-DMA (Direct Memory Access) controller
-Programmable Interrupt Controller
-Programmable Interval Timer
-RTC chip (Real Time clock)
3. Keyboard Controller self test
4. Enable Keyboard Interface
5. Verify CMOS's basic R/W functionality.
6. Auto-detection of onboard DRAM & Cache
7. Copy the Bios form ROM (READ ONLY MEMORY) into E0000 - FFFFF shadow
RAM, so that POST will go faster .
8. Test the first 256Kb DRAM
9. Initialize the first 32 interrupt vectors with corresponding Interrupt handlers
- Initialize INT No. from 33 - 120 with (Dummy spurious) Interrupt Handler
10. Issue CPUID instruction to identify CPU type
11. Early Power Management initialization
12. Verify if the RTC time is valid or not.
13. Detect dead (bad) Battery = CMOS backup when no power is supplied to
main board.
14. PnP (Plug & Play) initializations including (PnP BIOS's only)
-Assign CSN to PnP ISA card
-Create resource map form ESCD
15. Assign IO & Memory for PCI devices .(PCI BIOS only)
16. Initialization of the BIOS Data Area. (40:ON - 40:FF )
17. Program some early Chipset's value according to Setup.
18. Measure CPU Speed for display & decide the system clock speed.
19. Video initialization including Monochrome, CGA, EGA/VGA. If no display device
found , the System speaker will beep. One medium long and three short beeps
20. Test Video RAM. (If monochrome display is found)
21. Show Messages including
- AWARD Logo, Copyright string, BIOS data code & Part No.
- OEM specific sign on messages
- Energy Star Logo (Green BIOS only)
- CPU brand, type & speed.
- Test system BIOS Checksum22. DMA channel 0 test
23. DMA channel 1 test
24. Test Timer0 counter 2
25. Test interrupt mask bit for channel 1
26. Test interrupt mask bit for channel 2
27. If EISA NVM checksum is good, execute EISA unitization. (EISA BIOS only)
28. Detect Base Memory & Extended Memory Size
- Test Base Memory from 256K to 640K
- Test Extended memory from 1Mb to the top of Memory
- Display the Award Plug & Play BIOS extension message. (PnP BIOS only)
- program all Onboard Super I/O Chips, including COM ports, LPT ports, FDD
port.......... according to setup value settings.
29. Set Flag to allow users to enter CMOS Setup Utility.
30. Initialize Keyboard & PS2 Mouse
31. Try to turn on Level2 Cache
- Note: Some chipset may need to turn on L2 cache n this stage. But
usually, the cache is turned on later in POST 61h (HEX)
32. Program the rest of the Chipset's value according to Setup.
- If Auto configuration is enabled , program the chipset with pre-defined Values.
33. Initialize Floppy (FDD) Disk Drive Controller.
34. Initialize Hard Drive (HDD) Drive Controller.
35. Test if this is a PnP BIOS, initialize Serial & Parallel ports.
36. Initialize Math Coprocessor
37. If there is any Error detected (such as Video ,Keyboard etc....) show all the
error message on the Screen & Wait for the user to press F1 key.
38. If Password is needed, ask for Password ,clear Energy Star Logo.
39. Write all the CMOS values in the BIOS stack area back into CMOS
40. Initialize all ISA ROM's
41. Later PCI initializations. (PCI BIOS only)
- assign IRQ to PCI devices
- initialize all PCI ROM's
42. PnP Initialization .(PnP BIOS only)
- assign IO, Memory, IRQ & DMA to PnP ISA devices
- initialize all PnP ISA ROM's.
43. Program shadow RAM according to Setup settings.
44. Program Parity according to Setup settings.
45. Power Management Initialization.
- Enable/Disable Global PM (Power Management)
- APM interface initialization (Automatic Power Management)
46. If it is NOT a PnP BIOS, initialize serial & parallel ports. Then Initialize Time
Value in BIOS data area by translate the RTC time value into a timer tick value.
47. Setup Virus Protection. ( Boot Sector Protection) Functionality according to setup
48. Try to turn on Level2 cache.
- NOTE: if L2 cace is already turned on in POST 3D, this part will be skipped.
- Set the Boot up speed according to Setup setting.
- Last chance for Chipset initialization.
- Last chance for Power Management initialization.
- Show the System configuration table.
49. Setup daylight saving according to Setup value.
- Program the NUM Lock, Typematic rate & Typematic Speed according to
Setup Setting
- If there is any changes in the Hardware configuration , update ESCD
information
- clear Memory that has been used
- Boot System via INT19H (HEX)
50. System Booting. This means the BIOS already passed the control to the
Operating System.End Bios Description
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