computer learning
1. Understanding Operating Systems
- A set of programs that monitor and regulate the use of computer resources
(Processor, main memory, file I / O devices, etc.).
- Bridging / liaison between the user (user program) with computer hardware.
2. Computer Operating System Functions
- As an Extended Machine (Virtual Machine)
a. Hiding the complexity of programming the hardware of the programmer or user.
b. Facility presents an easier and simpler to use the hardware.
- As a Resource Manager
a. Organize and make efficient use of computer resources (computer resources)
b. Its main task: to monitor the use of all resources; applying the rules (policy);
allocate the resources requested; take back (deallocation) resource
3. Computer Operating System Concepts
- Process
a. The process is a program that is being executed.
b. The process consists of: Executable programs; data and stack; Program counter; etc.
c. In timesharing system periodically rotating the operating system execution processes
available, usually based on a portion of CPU time.
d. When a process is suspended, then the process must be restarted
in the same state with the state when he was stopped.
• All information relating to the process must be saved. Generally
information is stored in the process table (array or linked list), one table for
each process.
• A process consists of: address space (core image) and attributes / information in the table
process
e. The main system call in the regulation process is associated with the manufacture and
dismissal of a process.
Example:
• Command interpreter or shell will read commands that the user typed in
terminals, and make the process run the command.
• If completed, then the process will run a system call to stop
himself.
f. A process able to create other processes called child process.
g. Operating systems can communicate with a process using the signal.
h. Signal can also be used for inter-process communication.
i. In multiprogramming systems, each process has a user identification (uid) derived
uid of the process owner.
- Files
Consisting of: pathname; Working directory: rwx (read, write, execute) code protection bits; File
descriptor / handle; Special files (block & character); Standard input; Standard output; Standard
error; Pipe
- System Calls
a. A set of "extended instructions" which is an interface between programs with
operating system.
b.System calls to create, to delete and use the objects governed by
operating system, among other things: the processes and files.
c. Library procedure put the system call parameters at a particular place and
provide instruction trap to start the operating system
d. Trap instruction: when received by the operating system, the system checks whether the parameter
is valid or not
e. Return the form of trap: the operating system returns control to the library procedure
f. Examples of mechanisms of system calls:
In a C program, system call to READ
count = read (file, buffer, nbytes)
