OPERATING SYSTEMS! Flashcards
Late 1940s
No OS, programmer was the user.
Programs were in binary, switches on machines.
One switch represented a bit.
Output was lights.
1950s
Use of punch cards to encode programs, which computers read.
Fed programs to machine, and they returned output.
Late 1960s and 1970s
Broken computer programs into smaller chunks, which could fit into the available memory at any one time.
80s and 90s
80s - Networking and communication.
90s - Move to open systems. OS designed for particular hardware.
e.g. MS-DOS
What is an OS?
Operating System is a program.
It is written, compiled, tested and debugged.
Software that makes hardware more useful and more user-friendly.
What does an OS do?
Environment to do work.
Helps user develop and run programs.
Starting and stopping Programs, and sharing the CPU between them.
OS Managing Memory:
which parts of memory that are in use and the ones that are free.
provides mechanisms by which programs can ask for more memory or give back memory they no longer need
OS Input and output
covers up the differences between alternative makes and models of devices
overlaps input and output with processing
Other things an OS does.
- File systems / organisation
- Protection
- one memory, one CPU : protect programs interference
- Networking
- covers up the differences between machines
- Error handling and recovery
Operating systems services
Set of functions provided by an operating system to enable a user to request service from it.
What is Kernel?
- Central component of OS
- Interface between hardware components and software applications
- Makes the software to interact with the hardware to get a specific task done.
- Decides the amount of resources (RAM, GPU,… ) to be used by every application.
Kernel continuted
- It decides on what programs to be executed and on what order.
has separate space on memory so it functions independently.
acts as a central authority which guides memory and keeps eye on all the hardware and software data flow.
System call:
Every process which starts on a system, demands the resources from kernel.
User Mode:
CPU can only execute a subset of its instructions – the more common ones, like add, subtract, load and store, etc. If a program is executed in user mode, it does not have access to memory, hardware and such resources .
Kernel Mode:
CPU can execute all of its instructions, including extra privileged instructions.If a program is executed in Kernel mode, it has direct access to memory, hardware and such resources .
