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When the first PC was introduced, the BIOS software containing all the device drivers for the entire system was collectively burned into one or more nonvolatile ROM chips and placed on the motherboard. In essence, the drivers were self contained, preloaded into memory, and accessible anytime the PC was powered on.Basic Input/Output Systems –also known as driver or drivers consists of low-level software that controls the system hardware and acts as an interface between the operating system and the hardware. BIOS are essentially the link between hardware and software in a system. The instant the PC is powered on, the BIOS might be mostly in ROM, but after XP is loaded, it resides entirely in RAM.BIOS functioned as a single entity even though programs were located in three different physical locations within the system.


Three Possible Sources of BIOS
  1. Motherboard ROM
  2. Adapter card ROM (such as that found on a video card) BYOB
  3. loaded into the RAM from disk (device drivers) or Websites
Four Major Functions in BIOS:
  1. POST –tests your computers processor, memory, chipset, video adapter, disk controllers, disk drives, keyboard, and other crucial components.
  2. Setup –the system configuration and setup program which enables you to configure the motherboard and chipset settings along with the date and time, passwords, disk drives, and other basic system settings.
  3. Bootstrap Loader –a routine that reads the first physical sector of various disk drives looking for a valid Master Boot Record (MBR).
  4. ROM (BIOS) –the collection of actual drivers used to act as a basic interface between the operating system and your hardware when the system is booted and running.
Read Only Memory contains a Power on Self Test (POST), a bootstrap loader, and a setup program. When the OS was loaded, the drivers were preloaded into the ROM to interact with the hardware.  ROM is the only Non-Volatile Memory.
Complementary Metal-Oxide Semiconductor otherwise called RTC/NVRAM (Real-Time Clock/Non-Volatile Random Access Memory)
Non-Volatile –requires very little power usually by a battery (lithium coin cell batteries can last up to 5 years).
BIOS setup settings are written to the storage area of RTC/NVRAM.
Adding new drivers to the motherboard ROM has been extremely difficult because ROM chips were difficult to change and limited space was available. Most of the 128KB of motherboard ROM was used for existing drivers, POST, BIOS setup, and bootstrap loader.
Two choices for installing new hardware:
  1. Adapter cards held onboard ROM containing the device drivers.
  2. In the early stage of loading, the OS startup file (IO.SYS) checked for a configuration file (CONFIG.SYS) that specified any additional drivers to load to support new hardware. In essence, these drivers were loaded from disk into RAM and linked into the BIOS so they could be called on when necessary.
ROM Shadowing –in virtually all systems the ROMs are shadowed, which means they are copied into DRAM chips at startup to allow faster access during normal operations. Performance gain is often slight, and can cause problems. It is wise to only shadow the motherboard. It’s only useful in 16-bit operating systems, and completely useless in Windows XP (32-bit drivers replace the 16-bit BIOS code in RAM).
ROM (Read Only Memory) Mask
  • Cast in –the binary data was integrated in the die which represents the actual silicon chip itself.
  • Nobody uses Mask ROMs anymore
PROM (Programmable Read Only Memory) Burned
  • OPT (One Time Programmable)
  • Technically, there programmed with binary 1s
  • Gang programmer –device used as a PROM burner
EPROM (Erasable Programmable Read Only Memory) UV-Erased
  • Clear quartz crystal window directly over the die
  • UV light erases the chip by causing a chemical reaction, restoring the chip (new)
  • Standard room light will degrade the chip
  • EPROM eraser –erases the EPROM chip
EEPROM / Flash ROM (Electrically Erasable Programmable Read Only Memory)
  • Electronically programmed or erased directly in the circuit board
  • Virtually all PCs and automobiles use EEPROMs since 1994 or 1996
  • Sometimes Flash ROM is write-protected, which you must disable before you upgrade, by means of a jumper or a switch.
  • Identified by a 28xxxx or 29xxxx part number
AMI (American Megatrends, Inc.) [keystroke = Delete]
Phoenix Technologies [keystroke = F2]
Award Software –bought by Phoenix Technologies in 1998; [keystroke = delete]
OEMs (Original Equipment Manufacturer) must be either AMI or Phoenix.
Although some OEMs make their own BIOS ROMs (Compaq, AT&T, and Acer)
Microid Research (MR) BIOS –markets upgrade BIOS for Pentium and 486 motherboards
Do not go to the BIOS manufacturer for an upgrade, Go to the motherboard manufacturer.
If systems dating from 1995 don’t have Flash ROM (replace it).
ROM chips –very slow with access times of 15ns
DRAM –access times of less than 10ns
Maintenance–specifies the processor speed and clears the setup passwords.
  • Speed locking
Main–allocates resources for hardware components.
  • Time/date
Advanced–specifies advanced features available through the chipset
  • Autodetect –detects drivers every time you boot up
  • PnP configuration –determines which system resources are available.
Security – specifies passwords and security features.
  • Supervisor password –to view or change all the setup options
  • User password –system is allowed to boot
  • Most systems have a jumper on the board to clear passwords
Power –specifies power management features
  • APM (Advanced Power Management) –done by the hardware
  • ACPI (Advanced Configuration and Power Interface) –done by the OS
    • ACPI with PnP is controlled with your OS.
    • ACPI error codes
      • Red screens –hardware or BIOS
      • Blue screens –software or obscure problem
Boot –specifies boot options and power supply controls.

Exit –saves or discards changes to the setup program options.

Windows 95, 98, and Me allowed the use of both 16-bit and 32-bit drivers, easing the transition to full 32-bit operation. Windows NT, 2000, or XP use 32-bit drivers that were designed to be loaded from disk to replace all the drivers in the motherboard ROM. 64-bit versions of Windows could not use 32-bit or 16-bit drivers.
Extended Memory is located in System RAM
PnP device must contain a PnP device ID.
Two machines with different processors, storage media, video display units, and so on can run the same OS and applications.
It did NOT matter where the driver was. As long as the routine existed at a Memory Address, it could be called.
Low-Level Routines (Device Drivers)
Assumed Hardware/Basic System Components
  • Keyboard
  • Floppy Drive
  • Hard Drive
  • Serial Port
  • Parallel Port
  • And more