- This stands for basic input output system
- When a computer is first switched on it looks to the BIOS to get it up and running and so the processors program counter points to the BIOS memory
- The BIOS will usually first check that the computer is functional, memory is now installed and accessible, the processor is working, this is called is power on off self test (POST)
- once it is finished it can use a boot loader program to load the operating system kennel into memory.
- BIOS usually stored on flash memory so it can be updated which allows settings like the boot order disks to be changed and saved by the user.
Virtual Machines
- It is possible to write a program that has the same functionality as a physical computer, this is called virtual machines
- A common virtual machine is run operation with another operating system, this might be because a program is needed that will not run on the host operating system or it might be because it offers a convenient way to test a program being developed on multiple platforms.
- virtual machines are just programs and data that have advantages over physical machines, they can be backed up and duplicated and more than one can be at one time on a physical machine. It is for these reasons that many organisations are vitalising their network infrastructure, making their server a group of machines running from a cluster of physical machines.
Process Virtualisation
- Another common use of virtual machine is for interpreting intermediate code. When programs are compiled to a machine that code will only run on processors with the same instruction set
- An alternative is to use an interpreter, but this is slow and means that the source code is freely available.
- Intermediate code offers a compromise between the two approaches.
- A compiler is needed to convert the source into something called a byte code.
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