Programs To Access System Resources

DIAGRAM OF DISK PLATTER

Accessing a raw disk involves the data, the disk drive, the track location(s), and the sector location(s) within the corresponding tracks.
However, at the application level, at programmer may prefer to specify a file and the location of updates, without worrying about the underlying physical complexity of the disk.
 3.2    COORDINATION
A simple of coordination is protection. An operating system needs to protect different application from each other and crashing the operating system.
Preventing applications from crashing each other is mainly achieved by making instances of applications run in different address spaces. Literally, an address space defines all memory address that an instance of application can touch.
Preventing applications from crashing the operating system is commonly achieved by having dual-mode operations. When the operating system is running (e.g., the CPU is running under the user-mode), an application can only access states within its own address space.
Note that if the operating system is dedicated to single application, dual- mode operations are not required.
3.3    TYPES OF OPERATING SYSTEM
a)    SINGLE AND MULTI-TASKING: A single-tasking system can only run one program at a time, while a multi-tasking operating system allows more than one program to be running in concurrency. This is achieved by time-sharing, dividing he available processor time between multiple processes which are each interrupted repeatedly in time-slices by a task scheduling subsystem of operating system. Multi-tasking may be characterized in pre-emptive and co-operative types. In pre-emptive multitasking, the operating system slices the CPU time and dedicates a slot to each of the programs. UNIX-like operating systems, e.g., Solaris, Linux, as well as AMIGAS operating system supports pre-emptive multi-tasking. Cooperative multitasking is achieved by relying on each process to provide time to the process in a defined manner. 16-bit version of Microsoft Windows used cooperative multitasking. 32-bit versions of both Windows NT and Win9x, used pre-emptive multi-tasking.
b)    SINGLE AND MULTI-USER: Single-user operating systems have no facilities to distinguish users, but may allow multiple to run in tandem. A multi-user operating system extends the basic concept of multi-tasking with facilities that identify processes and resources, such as disk space, belonging to multiple users, and the system permits multiple users to interact with the system at the same time. Time-sharing operating systems schedules tasks for efficient use of the system and may also include accounting software for cost allocation of processor time, mass storage, printing, and other resources to multiple users.