E2011: Theoretical fundamentals of computer science
Basic concepts about operating systems
Vlad Popovici, Ph.D.
Fac. of Science - RECETOX
Outline
1 Operatings systems
2 Kernel
3 Shell
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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 / 16
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
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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 / 16
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
CPU
batch 1
batch N
job 1
job 1
OS
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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 syste8 / 16
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
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OS Kernel - main functions
loading and managing less-critical OS components, such as device
drivers
managing exectution 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
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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
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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)
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Figure: Comparison of three different kernel types (from Wikipedia)
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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
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Shells
Vlad Popovici, Ph.D. (Fac. of Science - RECETOX)E2011: Theoretical fundamentals of computer science Basic concepts about operating syste15 / 16
Questions?
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