Introduction to Computers BIOS

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

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

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

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

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

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

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

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

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

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