quartz/content/notes/13-OS-intro.md

title	aliases	tags	sr-due	sr-interval	sr-ease
13-OS-intro		cosc204 lecture	2022-11-23	22	230

why learn OS

• security
• optimisation
• wierd bugs
• "crown of programming"
• understand hardware better
• embedded sys and IoT
• co-design of hardware and software

what is an OS

• a program (also called OS kernel) loaded onto RAM first when pc is turned on
• OS kernel (in kernel space) has highest privilege and can access any hardware directly
• user programs (in user space) cannot acces hardware unless permitted otherwise by the OS kernel via service request (sys call)

a program (OS kernel) that manages the different aspects of the opereration of the machine and runs with the highest privilege in a protected domain

manages: - processes - data storage - ram, file systems - io devices - network - ui - security and protection

kernel vs user space

• cpu can check space of software via flag in status word
• when interrupt or sys call occurs, the flag is ser to kernel space
• kernel
  • protected space where software can access hardware
  • OS kernel is run in kernel space
• user
  • other software is run in user space
  • non privilege space where softwar cannot access hardware
  • unless permitted by kernel

process management

a process is a program in execution

• a program is not a process

process management involves

• creating and deleting processes
• scheduling processes
• suspending and resuming processes
• process synchronisation
• process communication
• deadlock handling

storage manangement

storage:

• primary (RAM)
• secondary (hard drive)
• tertiary (floppy disks, tapes, cd, etc)

storage manangement involves:

• Allocating and deallocating storage
• Keeping track of storage in use and free storage
• Transferring data between primary and secondary storage

Defn: the file system is the mechanism by which the user accesses/manipulates sotred data in secndary storage like hard disk

io device managment

• A computer system can include a very wide range of I/O devices: keyboards, mice, printers, hard disks, CD-roms, etc etc etc.

I/O device management includes tasks like:

• tracking the status of each device
• allocating devices to particular processes
• deallocating devices
• scheduling tasks for individual devices (e.g. disk scheduling)
• these functions are built into modules called device drivers; each device needs one device driver to manage the hardware and serve the requests from user applications via the OS kernel.

UI

Defn: the shell is the program through which the user interactins with the operating system

two types:

• icon based point and click
• keyboard commands e.g., UNIX
  • harder to learn but more powerful and flexible

history

• No OS
• batch systems
• spooling
• time sharing
• real time