E2011: Theoretical fundamentals of computer science
Basic concepts about operating systems
Vlad Popovici, Ph.D.
Fac. of Science - RECETOX
Outline
1 Operating systems
2 Kernel
3 Shell
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste2 / 20
Physics: electrons
Transistors, diodes -
devices
Analog circuits:
amplifiers, filters
Logic: adders,
memory
Digital circuits: gates
Microarchitecture:
data paths,
controllers
Architecture:
instructions,
registers
Operating system:
device drivers,
kernels
Application software:
programs
Abstraction
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste3 / 20
Operating systems
Why?
acts as an interface between user/applications and hardware
resource manager: manages I/O and peripherals
provide a virtual perspective on the underlying hardware
manage programs
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Main roles of the OS:
resource sharing:
▶ allocate resources for all
activities; separate the
resources between activities
▶ isolation of activties
▶ communication between
processes/activities
virtualization
provide standard services:
process management, file
systems, network services, etc
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste5 / 20
OS over time
early OS: set of routines for common procedures; single-user OS
multi-user OS: → batch processing → multi-tasking → virtual
machines
time-sharing OS: interactive use
modern OS: usually a kernel+GUI; desktop-level (MacOS, Linux,
Windows, etc); smart appliances (Android, iOS, Symbian, etc);
server-level: GUI is optional (UNIX-based OSes, etc); etc
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste6 / 20
Batch OS
intially, a system in which
jobs are run sequentially
a job monitor supervises
execution and manages the
job queue
modern OSes have their own
job scheduler(s) allowing for
non-interactive, eventually
synchronized, execution of
jobs
Job 1
Job J
OS
Batch 1
Batch N
CPU
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste7 / 20
Example of batch OS
IBM’s
OS/360
developed in the 1960s
designed for mainframes
goal was to maximize
hardware utilization
introduces job control
language (JCL)
Examples:
start a job: job name, accounting
information, params
//MYJOB JOB (ACCOUNT),’MY JOB
NAME’,CLASS=A,MSGCLASS=X
specify program to execute within job
//STEP1 EXEC PGM=MYPROGRAM
conditional execution
//STEP2 EXEC
PGM=ANOTHERPGM,COND=(0,LT,STEP1)
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste8 / 20
Multitasking
”concurrent” exectution of processes (tasks)
does not imply parallel execution
multiprogramming OSes: allow context switching between processes
cooperative multitasking: processes voluntarily ceed time to OS/other
process: ealry Windows and MacOS
preemptive multitasking: OS decides to switch between executing
tasks
real time systems
multi-threaded systems
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste9 / 20
Example of multitasking OS
UNIX
developed in the 1970s
at Bell Labs
implements preemptive
multitasking
time-sharing: CPU time
dived among multiple
processes
process management
system calls for process
control: fork, exec,
kill, etc
Examples:
work with files: ls, cp, mv, rm
traverse filesystem hierarchy: cd, pwd
control access: chmod, chown
control processes: ps, kill
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste10 / 20
Another classification of modern OSes
1 Desktop OSes: for personal computers, user-friendly, wide range of
applications; ex: Windows, macOS, Linux
2 Mobile OSes: for touch interfaces and mobile devices; ex: Android,
iOS, HarmonyOS.
3 Server OSes: manage and optimize network resources, security, and
multi-user services; ex: Windows Server, Linux
4 Embedded OSes: for specific hardware and applications; ex:
FreeRTOS, Embedded Linux, VxWorks, QNX.
5 Real-Time OSes: when immediate response to inputs is critical; ex:
RTLinux, FreeRTOS, QNX, LynxOS.
6 Mainframe OSes: for high-volume processing; ex: IBM z/OS,
Unisys OS 2200, HP NonStop OS.
7 Distributed OSes: coordinates multiple computers ex: Apache
Hadoop (for data processing clusters), Google’s Kubernetes OS (for
container management), Plan 9 from Bell Labs.
8 Network OSes: used for managing networked computers; ex: Novell
NetWare, Cisco IOS, Windows Server with Active Directory.
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste11 / 20
OS Kernel
kernel: the core of the OS that provides services to all other
components of OS
talks directly to hardware
usual start-up sequence: power-on → BIOS (Basic I/O System) →
kernel loaded into a protected memory space
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste12 / 20
OS Kernel - main functions
loading and managing less-critical OS components, such as device
drivers
managing execution threads and various processes spawned by
running applications
scheduling applications
memory management
managing and optimizing hardware resources and dependencies
managing and accessing I/O devices (keyboards, mice, disk drives,
USB ports, network adapters and display,...)
handling device and application system calls using various
mechanisms such as hardware interrupts or device drivers
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste13 / 20
CPU modes to support kernel:
kernel mode: code has unrestricted access to hardware; it is loaded in
protected memory space and operates with highest privileges
user mode: applications run with lower privileges; access to resources
is made via system calls to kernel
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste14 / 20
Types of kernels:
microkernel: delegates user services and processes in different address
space; uses message-passing for communication; more flexibility and
security (e.g. QNX - UNIX-based, real-time)
monolithic: implements services in the same address space (e.g. most
of UNIX-based kernels, Windows 9x)
hybrid: tries to combine both (e.g. Windows 10, 11)
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste15 / 20
Figure: Comparison of three different kernel types (from Wikipedia)
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste16 / 20
Shells
a program that allows users and programs to interact with OS services
two modes: command line interface (CLI) and graphical user interface
(GUI)
CLI it has a specific language allowing the on line or scripted
interaction with OS
examples of CLI: Windows’ Power Shell or UNIX’s bash, tcsh, etc
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste17 / 20
Shells
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste18 / 20
Questions?
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste19 / 20
Explorations
go to https://copy.sh/v86/ and instantiate some machines with
Windows, DOS, and Linux and try to find your way around
alternatively, try https://www.pcjs.org/ for a more diverse
selection of OSes (and other older programs)
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste20 / 20