Why OS?

To protect and to serve (from NYPD)

Operating System (kernel) is a software that converts hardware into a useful form for applications.
Middleware, Software Development Environment (compilers, loaders, editors, libraries, ...) are not OS!

History of OS

1G (1945 ~ 1955)

Vacuum tubes and plugboards

No programming/assembly languages!
Obviously no OS (coded with 0 or 1)

2G (1955 ~ 1965)

Transistors and mainframes

Batch systems - Submit program and run it (e.g. using cards) Can run only one job at a time

OS is always resident in memory and merely transfers a control (just a library).

Problem) CPU is underutilized due to the bottleneck in I/O (e.g. Card readers, tape drivers, line printers)

3G (1965 ~ 1980)

IC (Integrated Circuits), disk drives

Multiprogrammed systems - Program as jobs, CPU utilization increased!

Now looks like a real OS:

• Job scheduling
• Memory management
• CPU scheduling
• Concurrency
• Protection
• Spooling

Even better: Time sharing systems - Program as process, response time improved!

More OS features:

• Sophisticated CPU scheduling
• Virtual memory and swapping
• File system
• Synchronization
• IPC (Interprocess communication)
• Interactive shell
• More protection

4G (1980 ~)

Microprocessors (LSIs, VLSIs)

Era of personal computers!

Modern OS features:

• GUI (Graphical User Interface)
• Multimedia
• Internet & Web (Network stack)
• Mobile / Networked / Distributed
• Threads
• Virtualization

Multics

Multiplexed Information and Computing Service

First time-shared, multi-processor OS!
Very influential; Nearly every feature was made from Multics!

They claimed they would create an OS that combined all existing technology at the time, but it failed... (c.f. second-system effect)

• Hierarchical file system
  • ACL (Access Control List)
  • Hard / symbolic links
• Virtual memory (segmentation and paging)
• User-level command shell
• Dynamic linking, shared memory
• Implemented in high-level language (PL/I)
• Logical disk volumes
• Supports every programming languages at that time (e.g. Fortran, Lisp, C, Cobol, ...)

Unix

Bell labs was tired of slow development of Multics, so they quit and made Unix.

Motivation) Putting everything is impossible, only implement necessary features!

• Hierarchical file system
  • Special files: Everything is file (e.g. I/O, drivers, ...), we can use uniform I/O, naming, and protection
  • Removable file systems via mount/umount
  • i-node (metadata)
• Process control
  • e.g. fork, exec, wait, exit
  • Pipes for IPC
• Shells
  • Standard I/O and I/O redirection
  • Filters, shell scripts
• Signals

OS

• Virtualization: How to make each application believe it has each resource to itself?
• Concurrency: How to handle concurrent events correctly and efficiently?
• Persistence: How to make information survive power loss?

Application view

OS provides an abstract view of the underlying computer system.

Abstractions:

• CPU cores -> processes, threads
• Physical memory -> Virtual memory
• Storage -> Volumes, directories, files
• I/O devices -> Files

System view

OS manages various resources of a computer system.

Manages resources:

• CPU
• Memory
• I/O devices
• Queues
• Energy

by:

• Sharing (time, space, ...)
• Protection
• Fairness
• Efficiency

Implementation view

OS is highly-concurrent, event-driven software.

Two kinds of events:

• System calls (by software)
• Interrupts (by hardware)