Skip to main content - controls low level software that controls specific hardware
- It is held in non-volatile memory devices such as ROM, EPRMO, or flash memory
- Firmware can be upgraded on consumer electronics devices like dvd players, refrigerators, TVs, music systems, etc.
Northbridge and Southbridge
- in computers, CPUs need a way to communicate with I/O devices like keyboards and mice
- in the past there were separate controller chips for each device type
- these got consolidated into two paired chips called the northbridge and the southbridge
BIOS
- The basic input/output services (BIOS) helps provide information about devices to the CPU
- Programs that help the CPU communicate with the devices are called services or device drivers
- Motherboard store keyboard, mouse controller, support programs on a ROM (read-only memory)
- Updating the BIOS firmware is called “flashing the BIOS”
UEFI
- All current systems are unified extensible firmware interface UEFI instead of BIOS
- UEFI supports booting to partitions larger than 2.2 TB and handles all boot loading duties
- UEFI firmware native 32/64 bit
- Portable to other chip types, not just 16-bit x86
- Apple computers have EFI and CMOS, but Apple designs their systems form the ground up as unified systems
CMOS
Power-On Self Test
- Computer turns on or reset, initiates power-on self test
- POST program does health check
- POST doesn’t actually do any diagnostics
Beep Codes
- POST errors are displayed on the screen as text
- Old computers has many beeps during POST
- Modern computers have two main beep codes
- One long beep then two or three short beeps (video card)
- single repeating beep (RAM)
- use a POST card to help troubleshoot the cards
Boot process
- Internal power supply turns on and initializes
- processors first starts up and ready
- the BIOS performs the power-on self test (POST)
- BIOS looks for the video card
- BIOS looks for other devices ROMs and BIOSs
- BIOS displays its startup screen
- BIOS does more tests on the system - memory count up, system inventory
- BIOS detects and configure plugand play devices
- BIOS will display a summary screen of the configuration
- BIOS begins the search for the drive to boot from
- BIOS looks for boot information to start the operating system boot process
- Code in the boot sector takes over from the BIOS