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BIOS and CMOS

BIOS and CMOS. Adding personality to your PC. We Need to Talk!. The CPU needs some method to talk to the devices to tell them what to do The devices need some way to send data to, and receive data from the CPU We need to expand our logical model from the CPU chapter. RAM. Northbridge. CPU.

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BIOS and CMOS

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  1. BIOS and CMOS Adding personality to your PC

  2. We Need to Talk! • The CPU needs some method to talk to the devices to tell them what to do • The devices need some way to send data to, and receive data from the CPU • We need to expand our logical model from the CPU chapter

  3. RAM Northbridge CPU Address Bus EDB

  4. RAM Northbridge CPU Address Bus EDB Southbridge keyboard Video Card Hard Disk Drive

  5. Chipset Address Bus Northbridge RAM CPU EDB Chipset Southbridge Keyboard Controller Video Card Hard Disk Drive

  6. 845 Chipset

  7. 925 Chipset

  8. Keyboard • How we communicate with the keyboard

  9. Problems • Different motherboards have different keyboard controllers • We need specific code to talk to the controller • We need a place to store this specific programming and the programming for other devices (optical drive, floppy, etc.)

  10. Solution • Use a ROM chip • Does not “forget” when power is removed, like RAM does • Specific to motherboard and devices on it • Read only, code does not change • Can hold lots of programs, like a “chapter book” • Called “firmware”

  11. IBM’s BIOS BIO BIOS Patent “fence” around BIOS

  12. Making a ROM chip • We “burn” the code into the chip: 1 0

  13. System ROM • Holds all the support programming for basic devices • Is given a specific address space, or range of memory addresses for its code

  14. The First Megabyte 1 MB • Upper Memory • Conventional Memory (384 KB) 640 KB Address 0

  15. CPU Mouse Keyboard Video card RAM Network card Sound Card Floppy drive Hard Disk drive Zip drive USB ports CD-ROM drive Basic Hardware

  16. Basic Hardware • CPU • Mouse • Keyboard • Video card • RAM • Network card • Sound Card • Floppy drive • Hard Disk drive • Zip drive • USB ports • CD-ROM drive

  17. Stored Information • Stores access/write code for keyboard • Stores access/write code for system speaker • Stores access/write code for other chips (functions) on motherboard • Does not change (more on this in a moment)

  18. CMOS • Complimentary Metal Oxide Semiconductor – how it was made • Stores specific information about your system: • Amount of RAM present • Type of hard disk drive • Date and Time • Needs battery power to “remember” when power is off

  19. Chipset Address Bus Northbridge RAM CPU EDB Chipset Southbridge BIOS And CMOS Keyboard Controller Video Card Mouse 20

  20. BIOS • All devices need BIOS code to interoperate with CPU. Some is stored directly in System BIOS chip, most is stored elsewhere. • One of the functions of BIOS is to provide the CMOS Setup Utility, or Setup, which allows us to change CMOS data.

  21. BIOS information CMOS information

  22. CMOS or Setup • Option to use this program is early in the boot cycle – long before system loads Operating System • Different key(s) to enter different Setups • You should only get to Setup on purpose • Program stored in BIOS, but only edits data in CMOS • First CMOS was set of switches!

  23. Who makes BIOS? • Award Software • Phoenix Technologies • AMI – American Megatrends Inc. • They write BIOS with lots of options; motherboard maker picks sections to be used • Long gone are IBM’s patents on BIOS Same parent company

  24. Setup • Lots of screens and subscreens • You don’t need to know about all settings on all screens • Motherboard book is mildly helpful on some options • You should know generally where things can be found

  25. Date and Time and … • Usually on the first screen, or first menu choice • Lets you set Date, Time, floppy present (will autodetect it), memory count, hard drive(s) present (again, autodetected)

  26. Here is where you set the boot order

  27. When adding a modem, you might want to turn both of these off.

  28. Old CMOS • Stored the hard drive “geometry” which was NOT found on the drive’s label • Old systems had a nasty habit of loosing CMOS data and requiring a trip to the repair shop to get fixed • I spent many an hour hacking drive geometry values by trial and error 15

  29. New CMOS • Did you notice the “High Performance” option? • Did you see the “Setup Defaults” option? • BIOS can “talk” to hard disk drive and get all the information it needs. • About the worst that happens today is the need to reset date and time.

  30. Chip Evolution • EPROM – Erasable Programmable ROM; used ultra-violet light (sunlight) to erase • EEPROM – Electrically Erasable – what we use today • Flash ROM – another name for EEPROM • NVRAM – Non-volatile RAM. Really not so, still needs battery power

  31. The Three-In-One • We have BIOS that stores code and access program to CMOS • We have CMOS that stores changeable information about our system • We have RTC (Real Time Clock) that keeps track of date and time • All three are now rolled into one chip

  32. Easy way to spot this chip is by the shinny label

  33. About that Battery • Should last 5 to 10 years • You can find them at Savon even • If your system forgets date and/or time, it’s time to replace the battery • Beware the evil ESD!

  34. More Battery • Sometimes we WANT to reset CMOS: • A forgotten password • Too aggressive overclocking • Incorrect low-level settings on some screen • Either move the jumper, or pull the battery • Do either for about 10 seconds • If you are to pull battery, make sure you unplug system too

  35. 10

  36. More BIOS • Option ROM – put a BIOS chip on the card/device • Video is most common for this • SCSI cards • Network cards have socket, chip is extra

  37. Software Solutions • Device Drivers – very flexible, but must wait until OS starts loading. • CONFIG.SYS – DOS utility program, runs before DOS really gets going • SYSTEM.INI – Introduced with Win 1 to 3, another text file. Win 9x won’t boot without it; XP will • The Registry – Introduced with Win 95. Binary database of information

  38. Software Help • Control Panel – Graphical “window” to the Registry • Device Manager – Another graphical path to the Registry • REGISTRY EDITOR(s): • REGEDIT • REGEDT32

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