System Programming Basics

Cha#2H.M.Bilal

Operating Systems

•An operating system is the software on a computer that manages the way different programs use its hardware, and regulates the ways that a user controls the computer.

• Operating systems are found on almost any device that contains a computer with multiple programs—from cellular phones and video game consoles to supercomputers and web servers.

•Some popular modern operating systems for personal computers include Microsoft Windows, Mac OS X, and Linux

Hardware Abstraction Layer

•A hardware abstraction layer (HAL) is an abstraction layer, implemented in software, between the physical hardware of a computer and the software that runs on that computer.

•Its function is to hide differences in hardware from most of the operating system kernel, so that most of the kernel-mode code does not need to be changed to run on systems with different hardware.

•On a PC, HAL can basically be considered to be the driver for the motherboard and allows instructions from higher level computer languages to communicate with lower level components, such as directly with hardware.

•The Windows NT operating system has a HAL in the kernel space, between hardware and kernel, drivers

•This allows portability of the Windows NT kernel-mode code to a variety of processors, with different memory management unit architectures, and a variety of systems with different I/O bus architectures