operating system

1.5
Modern OS are interrupt driven. Events are almost signaled by the occurrence of an interrupt or a trap, which caused either by an error or by a specific request from a user program that an OS service be performed .Dual-mode Operation allows OS to protect itself and other system components whereas Multimode Operation increasingly CPUs support multi-mode operations.
System call provides the means for a user program to ask OS to perform OS tasks on the user program’s behalf. When a system callis executed, it is treated by H/W as a S/W interrupt.
Timer protects CPU resource from getting stuck by a user program. To ensure OS maintains control over the CPU, a timer can be set to interrupt the computer after a specified period. Use it to prevent a user program from running too long.
1.6
A process is a program in execution. It is a unit of work in the system.
A program by itself is not a process. It is a passive entity, like the contents of a file stored on disk, whereas a process is an active entity.
1.7
To improve CPU utilization and responsive time, general-purpose computers must keep several programs in memory, creating a need for memory management.
1.8
OS provides a uniform, logical view of information storage.
Caching is an important principle, performed at many levels in a computer and an information in use copied from slower to faster storage temporarily. There are Hardware cache and Software-controlled cache.
Cache Coherency in Multiprocessor Environment. Must make sure that an update to the value of A in one cache is immediately reflected in all other caches where A resides.
1.9
Protection refers to any mechanism for controlling the access of processes or users to the resources defined by a computer system.
Security is to defend a system from internal and external attacks.
1.10
Kernel Data Structures is the fundamental data structures used in OS.
1.11
Computing Environments
Traditional Computing
Mobile Computing
Distributed Systems
Client-Server Computing
Peer-to-Peer Computing
Virtualization
Cloud Computing
Real-Time Embedded Systems
1.12
Operating systems made available in source-code format rather than just binary closed-source