A. Real-time operating system
Real time Operating system is data processing
system in which time interval required to process and response the inputs is so
small that it controls the environment.
operating system has well defined, fixed time constraints otherwise system will
industrial control system, robots , weapons system , Air traffic control
two types of real time operating system
Hard real-time system:
Hard real-time system guarantee that critical task complete
Soft real-time system:
Soft real-time system are less restrictive.
GNU is a free software which is also called
“GNU’s not UNIX” because its design is very similar to UNIX, but have no unix
The combination of GNU software and linux
kernel is commonly known as linux.
C. Peer-to-Peer computing
Peer-to-Peer is another model of distributed
system which are connected with eachother via Internet. .P2P does not
distinguish between client and server. A node can act as both client or server.
Each peer in P2P network is equal to other peers. There is no center administrator
or any privileged peers. Computer or devices share the workload in the network.
Every resource is shared between peers . The shared resources can be processor
usage, disk storage space or network bandwidth.
Interrupt is sending an
event signal to CPU by any hardware or software mechanisms. Key point is
interrupts are asynchronous with respect to current process, typically indicate
that some device needs service.
Interrupt mainly can be
of three types
E. Solid-State disk
A solid state drive is a
high-performance plug-and-play storage device that contains no moving parts.
SSD components include either DRAM or EEPROM memory boards, a memory bus
boards, a CPU and a battery card.
Because they contain
there own CPUs to manage data storage, they are a lot faster than conventional
rotating hard-disk; therefore they produce highest possible I/O rates.
F. Shell script
A shell script is a text file that contains a
sequence of commands for a UNIX-based operating system. A shell script allow us
to program commands in chains and have the system execute them as a scripted
event, just like batch files. Each shell script is saved with .sh file extension. A shell Script can
provide a convenient variation of a system command where special environment
settings, command options, or post-processing apply automatically. But in a way
that allows the new script to still act as a fully normal unix command .
G. System calls
System calls are programming interface to the
services provided by the OS. Application developers often do not have direct
access to the system call, but can access through an application interface(API).
There are 5
different categories of system calls
H. fork() and exec()
fork() starts a new process which is a copy of
the one that calls it, while exec() replaces the current process image with
and child processes executed simultaneously in case of fork(), while controls
never return to the original program unless there is an exec() error.
I. System programs
System programs provide a convenient
environment for program development and execution. Some of them are simply user
interface to system calls; others are considerably more complex.
program can be divided in seven parts:
Programming language support
Program loading and execution
A microkernel is a minimalistic kernel
designed to be as small as possible. It contains only the basic code needed to
communicate with hardware and loading and operating system. Microkernels
generally contain less than 10,000 lines of code. They are able to maintain
small size by loading most system process in user mode rather than the kernel
Dtrace can be used to get a global overview of
a running system, such as the amount of memory, CPU time, file system and
network resources used by the active processes. It also provide much more
fine-grained information such as log of the arguments with which a specific
function is being called, or a list of the processes accessing a specific file.