1. Introduction to Computers
BIOS

2. BIOS
BIOS stands for basic input/output system. It is a firmware component that communicates between the hardware and operating system
Newer systems (and Macs) will have UEFI (Unified Extensible Firmware Interface) instead
When discussing BIOS we also usually include CMOS and EEPROM
CMOS (Complementary metal-oxide semiconductor) contains customizable data about your hardware (hard drive type and configuration, RAM type and configuration, boot device order, etc) This is considered legacy hardware
EEPROM (Electrically erasable programmable read only memory) has replaced CMOS, since it is non-volatile and doesn’t rely on a CMOS battery to retain information. The CMOS battery however still has its uses
Although they are legacy systems, the term BIOS and CMOS are used for BIOS/UEFI and CMOS/EEPROM interchangeably

3. UEFI vs Legacy Bios
UEFI offered a good deal of updates and improvements to BIOS
Offers faster, more efficient startup
Supports drives over 2.2 terabytes
Supports 64-bit firmware devices
Compatible with both BIOS and UEFI hardware
Tends to have a better user interface
Has security features to prevent malware attacks during boot

4. CMOS
BIOS is hard-wired read-only memory. It cannot be re-written, except by flashing the bios. It cannot be changed to accommodate changes in hardware, we need something that can be modified
CMOS is editable, and allows us to store values that are changeable when we upgrade our computer’s hardware: RAM amounts and configuration, hard drive storage space and access speed, etc
CMOS also keeps the computer clock updated
CMOS used to need a battery to keep data, but now the CMOS battery just keeps the system clock running

5. Device Types
Non-Configurable - These are devices that don’t have features that can be changed, or are unlikely to be replaced. For example the keyboard or system speakers. These can be handled by BIOS alone
Configurable - These are devices that have features that are changeable, but have to be in the system. These are devices like hard drives or RAM. The amount of RAM or storage can be upgraded and changes from system to system. These setting would be stored in CMOS
Custom - These are devices that may not be in the system; like network cards and video cards. Each will have different parameters and features. These require a different solution since we are unable to make BIOS or CMOS chips that will accommodate every possibility

6. Custom Devices
OPROM - Option ROM. This is firmware on the device designed to act as BIOS/CMOS for the device
Device Driver - This is a software solution loaded up by the operating system. This gives the benefit of easier updating, but it cannot be loaded and used during boot up
OPROM can also contain basic firmware drivers to bridge this gap and allow a basic firmware to be used before the software driver kicks in

7. PC Boot Process (POST)
Starting the system from off until the operating system can take over is perhaps the primary job for the BIOS. Here are the steps it takes
CPU start up
The CPU is the first device that gets powered up
It is hard-coded to look at one specific memory address on startup
This memory address will have a pointer to the BIOS
POST
The first task of the BIOS is POST - Power-on Self-test
POST first checks the BIOS for corruption
Second, it looks for a video card (installed or integrated) in order to display the rest of the process
Post then checks for other installed add-in cards
The final job of POST is to check to see if all of the devices necessary for running at a basic level like RAM and a keyboard

8. PC Boot Process (After POST)
Identify System Devices
BIOS uses its EEPROM and device-supplied information to identify system hardware. This is also where plug and play devices are allocated system resources
Identify Boot Drive
BIOS then searches for a boot device based on the boot order specified in CMOS
A boot device is a storage device with an operating system (or installer) loaded on it
Control of the system is then passed onto the boot loader
Load Operating System
The boot loader locates and loads the kernel of the operating system while configuring it for the hardware installed

9. Editing BIOS
To edit your BIOS settings we have to interrupt the boot sequence
This will usually involve pressing DEL, INS, or a function key like F1, F2 or F12, but it is completely dependent on the BIOS manufacturer
We will usually edit the BIOS to:
Change the POST time
Change the boot sequence
Enable/disable motherboard devices
Add a password to the BIOS to prevent unauthorized access
Each editor program will be different, so it is useful to be able to poke around an editor and explore it

10. System Diagnosis
BIOS not only provides us with basic information and editing capabilities, but they usually also provide diagnostic tools
Typically you can test your devices at a basic level, but then take time to run a more thorough test
For example, when you test your RAM, it can either run a basic test to see if it is responding correctly and able to read/write, or it can read and write individually to each bit to test them

11. Flashing BIOS
Manufacturers will sometimes release an updated BIOS. This could be to add new features or to patch a security vulnerability
The method to update the BIOS will change based on manufacturer, but in general we will need to go to the motherboard manufacturer’s website, download an application and run it or download the update directly to a CD or flashdrive to boot from
Either way the most important part: DO NOT INTERRUPT THIS PROCESS