Operating System Overview
CS-550: Comparative Operating Systems
Operating System
• A program that controls the execution of application
programs
• An interface between applications and hardware
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Operating System Objectives
• Convenience
– Makes the computer more convenient to use
• Efficiency
– Allows computer system resources to be used in an efficient
manner
• Ability to evolve
– Permit effective development, testing, and introduction of
new system functions without interfering with service
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Layers of Computer System
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Services Provided by the Operating
System
• Program development
– Editors and debuggers
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•
•
•
•
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Program execution
Access to I/O devices
Controlled access to files
System access
Error detection and response
Accounting
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Operating System as Resource Manager
• Responsible for managing all computer resources
• Functions same way as ordinary computer software
– It is program that is executed
• Operating system relinquishes control of the processor
to execute other programs
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Kernel
• Portion of operating system that is in main memory
• Contains most-frequently used functions
• Also called the nucleus
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Operating Systems History
• Early 1950s:
– Systems: Univac I, II; IBM 701, 704 – large, very expensive
• Serial Processing
– No operating system
– Machines run from a console with display lights and toggle
switches, input device, and printer
– Common concerns:
• Idle time between jobs
• Setup: running a job included loading the compiler,
source program, saving compiled program, and loading
and linking
• Every programmer writes routines to control I/O devices
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First Generation: Simple Batch Systems
• Eastern Joint Computer Conference in 1953: informal
discussion of IBM users
• GM develops input/output system for IBM 701
– Common set of procedures for access to I/O devices
– Monitor concept: Resides in main memory and controls the
running programs; Batches jobs together; Program branches
back to monitor when finished; Monitor starts next job
• GM and North American Aviation jointly develop
supervisor program for IBM 704
• ‘Share’ Operating System (SOS) developed by IBM on
709 for Share user group
– Supervisory control, buffered I/O, symbolic assembly
language
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First Generation: Simple Batch Systems (Cont.)
• Fortran Monitor System (FMS) on IBM 709
– Based on GM/NAA OS, first OS to support high-level
language programming
• Real-Time and Transaction processing Systems
– SAGE real-time control system (IBM AN/FSQ7 military
system)
– SABRE airline reservation system (IBM for American
Airlines)
• Tape Operating Systems
– Card input and output temporarily stored on tape
– Commonly used procedures (compilers) kept on tape
– Examples: TOS/360 for first S/360, TOS for RCA Spectra 70
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First Generation: Simple Batch Systems (Cont.)
• Disk Operating Systems
– Direct access to large amounts of data
– Operating systems provided by computer manufacturer
– Components: resident loader, Job Control Language (JCL),
Input/Output Control System (IOCS)
– Examples: Admiral for Honeywell 1800, EXEC I for Univac
1107, Scope for Control Data 6000, Master Control Program
for Burroughs 5000, IBSYS for IBM 709 and 7090
• ATLAS
– Developed by Manchester Univ. and Ferranti
– First use of interrupts, extracode (precursor of system call
instruction), and one-level store (precursor of virtual
memory)
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First Generation: Batch Multiprogramming
• Batch processing: each job submitted as a ‘batch’ of
cards
• Batch serial: jobs processed one at a time, each one
finishing before new one accepted
• Batch multiprogramming: several programs execute in
interleaved manner and share CPU, memory, I./O
devices – when a program waits for I/O completion,
CPU given to other program
• SPOOLing (Simultaneous Peripheral Operation OnLine)
– Spooler program reads jobs from cards and tapes onto disk
and copies output from disk to printer
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First Generation: Batch Multiprogramming
• Master Control Program (MCP) for Burroughs 5000
pioneered multiprogramming
– Virtual memory
– Priorities
– High-level languages (Algol, Cobol) supported using
compilers
• IBM System/360 family (1964)
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–
–
–
–
–
Evolvable: same program runs on entire family
DOS/360: interim disk OS
PCP: early version of OS/360
OS/MFT: batch multiprogramming for small S/360s
OS/MVT: batch multiprogramming for large S/360s
JCL: Large and powerful Job Control Language
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Time-Sharing Systems
• Disadvantages of batch systems:
– No direct user-program interaction
– Long turnaround time
• Interactive computing
– User and system programs on disk
– JCL commands entered by user directly on terminal
• Time-sharing systems
– Multiple users simultaneously access the system through
terminals
– Processor’s time is shared among the multiple users
– Time slice (time quantum) limits the amount of time (CPU)
received by each job
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Time-Sharing Systems (Cont.)
• Compatible Time-Sharing System (CTSS) developed in
early 60s by Project MAC at MIT on IBM 709, then
7094
• Dartmouth Time-Sharing System (DTSS)
– Dartmouth College with General Electric
– ‘Basic’ language developed for use on DTSS
• TOPS-10 developed by DEC for PDP-10
• TSS/360 developed by IBM for 360/67
– Virtual memory
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Time-Sharing Systems (Cont.)
• MULTICS developed by project MAC (MIT, Bell
Labs, GE) as successor of CTSS (1964)
– Hardware: modified GE635 (called GE645) with virtual
memory and protection support
– ‘Computing Utility’ concept
– Segmented virtual memory, linking and loading segments on
demand, files and segments treated the same
– ‘Rings of protection’
– Hierarchical file system
– Device independence
– I/O redirection
– Powerful user interface
– Written in a high-level language (PL/1)
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Abstract and Virtual Machines
• T.H.E. developed by Dijkstra at the Technological
Univ. in Eindhoven, Holland in late 1960s
– Major contributions to OS structuring and process
synchronization
– Structuring:
• Hierarchical structure made of layers
• Each layer, an abstract machine, i.e. apparent extension of
real machine
– Interacting processes (sharing common resources)
• Semaphores for process synchronization
• Deadlock solutions
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Abstract and Virtual Machines (Cont.)
• TENEX developed by Bolt, Beranek and Newman (BBN) for
the PDP-10 in early 1970s
– Time-sharing system with an abstract machine structure
• CP/CMS (Control Program/Conversational Monitor System)
developed by IBM Research in Cambridge, MA
– Virtual machine concept: apparent access to all machine features (virtual
memory, CPU, I/O devices)
– Hardware shared by several OSs (some being developed)
– Hardware:
• Modified S/360 model 40 (CP/40)
• Modified S/360 model 67 (CP/67)
– Product: VM/370 on S/370
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Minicomputer Operating Systems
• Mid-1950s: Burroughs E-101, Bendix G-15, Librascope LGP-30
– Machine language, no OS
• Early 1960s: CDC-160, IBM-1620
• Early 1970s: DEC OS-8 and TSS-8 for PDP-8
– Interrupts, DMA
• Disk Operating System for IBM 1800
• Oss named ‘keyboard monitor’ and ‘real-time monitor’
– Interactive interface for single user
– Run one program at a time
– Typical application: real-time control of lab. Operation
• DEC PDP-11 series
– OS (RT-11) simple single user
– RSTS time-sharing system
– RSX-11 real-time executive (multiprogramming, memory management,
file system, powerful command language)
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UNIX
• Early 1970s: Bell Labs winds down MULTICS participation,
Ken Thompson and Dennis Richie design a new OS
• Hardware: PDP-7 then PDP-11
• Key features
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Hierachical file system
I/O devices, special cases of files
Powerful command language: ‘Shell’
Redirection: input/output from/to any sourse/destination in a Shell
command
– Concurrent processes with inter-process communication
– Languages
• Assembly language initially (PL/I not available for PDP)
• Richie developed ‘C’ (BCPL  B  C)
• ‘C’ compiler for PDP-11 developed
• UNIX re-written in ‘C’
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Large Systems: Super-Minis and Main Frame Systems
• VAX/VMS for the VAX family from DEC
– Special instructions for OS support
– Extensive system services
– File management techniques
• UNIX implemented on the VAX
• OS/MVS (Multiple Virtual Storage)
– Upgrade of OS/MVT for time-sharing (S/370) based on the
Time-Sharing Option (TSO) developed for MVT
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Operating Systems for Micros
• Early OSs: MITS, IMSAI, Apple, Tandy, Heath
develop simple OSs (loaders, ‘Basic’ language)
running on Intel 8080, Zilog’s Z-80, Motorola’s 6800
• CP/M (Control Program for Microprocessors)
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Developed by Gary Killdall at Intel on 8008, then 8080
Single user OS
Simple interactive command interface
Basic I/O device management
Floppy disk based file system
Programming language for microprocessors (PL/M)
Killdall obtains rights to distribute CP/M, forms Digital
Research
– CP/M becomes dominant OS for micros
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Operating Systems for Micros (Cont.)
• CP/M limitations
– Limited user interface, file, and device management
– No memory management, no multiprogramming
• SCP-DOS from Seattle Computer Products
– Running on Intel 8086 (16-bit)
– New features: memory management, timer management, interrupt
support, sophisticated file system
• MS-DOS: Upgraded SCP-DOS to run on several processors
(SCP-DOS acquired by Microsoft)
• PC-DOS: Version of MS-DOS selected by IBM to run on their
PC
• UNIX influence:
– MS-DOS Version 2.0: Command interface like ‘Shell’, hierarchical file
system
– Later versions of MS-DOS: Multiple users, multiple processes
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Major Achievements
• Processes
• Memory Management
• Information protection and security
• Scheduling and resource management
• System structure
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Processes
• Definitions for the term process
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A program in execution
An instance of a program running on a computer
The entity that can be assigned to and executed on a processor
A unit of activity characterized by a single sequential thread of execution,
a current state, and an associated set of system resources
• Process components
– An executable program
– Associated data needed by the program
– Execution context of the program or process state (e.g., contents of
various processor registers, priority of the process)
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Memory Management
• Process isolation
• Automatic allocation and management
• Support for modular programming
• Protection and access control
• Long-term storage
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Information Protection and Security
• Access control
– Regulating user access to the total system, subsystems, and
data
– Regulating process access to various resources
• Information flow control
– Regulating the flow of data within the system and its delivery
to users
• Certification
– Proving that access and flow control perform according to
specifications and that they enforce desired protection and
security policies
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Scheduling and Resource Management
• The operating system:
– Manages the various resources: main memory space, I/O devices, and
processors, and
– Schedules their use by the active processes
• The resource allocation and scheduling policy must consider:
– Fairness
• Give equal and fair access to all processes
– Differential responsiveness
• Discriminate between different classes of jobs with different service
requirements
– Efficiency
• Maximize throughput, minimize response time, and accommodate as
many users as possible
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System Structure
• The size and complexity of operating systems have significantly
increased in time to meet the needs of new features and complex
hardware:
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CTSS: 32,000 36-bit words of storage
OS/360: 1 million machine instructions
MULTICS: 20 million instructions
Windows NT 4.0: 16 million lines of code
Windows 2000: 32 million lines of code
• Methods for structuring operating system software
– Modular software
– Hierarchical structure: hierarchical layers and information abstraction
• View the system as a series of levels
• Each level performs a related subset of functions
• Each level relies on the next lower level to perform more primitive
functions
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Operating System Design Hierarchy
Level Name
Objects
Example Operations
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Shell
User programming Statements in shell language
environment
12
User processes
User processes
Quit, kill, suspend, resume
11
Directories
Directories
Create, destroy, attach, detach,
search, list
10
Devices
External devices:
printers, displays
and keyboards
Open, close, read, write
9
File system
Files
Create, destroy, open, close
read, write
8
Communications Pipes
Create, destroy, open. close,
read, write
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Operating System Design Hierarchy
Level Name
Objects
Example Operations
7
Virtual Memory
Segments, pages
Read, write, fetch
6
Local secondary
store
Blocks of data,
device channels
Read, write, allocate, free
5
Primitive processes Primitive process,
semaphores, ready
list
Suspend, resume, wait, signal
4
Interrupts
Interrupt-handling
programs
Invoke, mask, unmask, retry
3
Procedures
Procedures, call
stack, display
Mark stack, call, return
2
Instruction Set
Load, store, add, subtract
1
Electronic circuits
Evaluation stack,
microprogram
interpreter
Registers, gates,
buses, etc.
Clear, transfer, activate,
complement
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Characteristics of Modern Operating
Systems
• Microkernel Architecture
– Only a few essential functions are assigned to the kernel
(address space, inter-process communication, and basic
scheduling)
– Other OS services are provided by processes (servers) that
run in user mode
• Symmetric MultiProcessing (SMP)
– There are multiple processors
– These processors share same main memory and I/O facilities
and are interconnected by an internal connection scheme
– All processors can perform the same functions
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Characteristics of Modern Operating
Systems
• Multithreading: process is divided into threads that can
run concurrently
– Thread
• Dispatchable unit of work
• Includes processor context
• executes sequentially and is interruptable
– Process
• A collection of one or more threads and associated system
resources
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Characteristics of Modern Operating
Systems
• Distributed operating systems
– Provide the illusion of a single main memory and single
secondary memory space
– State of the art for distributed operating systems lags that of
uniprocessor and SMP operating systems
• Object-oriented design
– Facilitates adding modular extensions to a small kernel
– Enables programmers to customize an operating system
without disrupting system integrity
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Windows 2000 (W2K): Brief History
• MS-DOS and PC-DOS
– DOS 1.0 released in 1981 had 4,000 lines of assembly
source code, ran in 8Kbytes of memory on a 8086
– DOS 2.0 in 1983 ran on the IBM hard-disk based PC XT
with 24Kbytes of memory resident OS
• Support for hard disk
• Hierarchical directories
• UNIX-like features: I/O redirection and background
printing
– DOS 3.0 in 1984 ran on the PC AT (80286) with 36Kbytes
– DOS 3.1, also in 1984, provided support for PC networking
– DOS 3.3, in 1987 ran on IBM PS/2 with 46Kbytes
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Windows 2000 (W2K): Brief History
• Need for a new operating system
– MS-DOS/PC-DOS did not use the full capabilities of the
evolving processors: 80286, 80386, 80486 and then Pentium
(e.g., extended addressing, memory protection)
– To compete with Macintosh, in 1990 Microsoft developed a
graphical user interface (GUI), Windows 3.0, that had to run
on top of DOS
• Microsoft and IBM attempt to jointly develop a
common operating system; attempt fails; IBM develops
OS/2 (multitasking, multithreaded), Microsoft develops
Windows NT
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Windows 2000 (W2K): Brief History
• Windows NT
– NT 3.1 released in 1993
• 32-bit operating system with ability to support older DOS and
Windows applications, as well as provide OS/2 support
• Same GUI as Windows 3.1
– NT 3.x, several versions
– NT 4.0
• Same internal architecture as 3.x
• Same user interface as Windows 98
• Several graphics components moved to NT Executive (kernel mode)
• Windows 2000 (W2K)
– Same Executive and microkernel architecture as NT 4.0
– New services and functions in support of distributed processing
– W2K Professional vs. W2K Server
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Single-User and Multi-User Multitasking
• W2K (like OS/2 and MacOS) was design to exploit the
capabilities of 32-bit microprocessors to meet the
increasing needs of new applications
• Motivations for multitasking
– Applications have become more complex and interrelated
(e.g., use of a word processor, a drawing program, and a
spreadsheet application simultaneously for a document)
– Growth of client/server computing: system needs to support
user interaction concurrently with inter-processor
communication
• W2K Professional supports single-user multitasking,
while W2K Server supports multi-user multitasking
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Windows 2000 Architecture
• Modular structure for flexibility
• Executes on a variety of hardware platforms
• Supports application written for a variety of other operating
system
• Currently, W2K is only implemented on the Pentium/x86
platform
• Separates application-oriented software from operating system
software
– OS software includes the Executive, the microkernel, device drivers, and
the hardware abstraction layer and runs in kernel mode (access to system
data and to hardware)
– Application software runs in user mode and has limited access to user
data
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OS Organization
• Modified microkernel architecture
– Not a pure microkernel: Many system functions outside of
the microkernel run in kernel mode (reason: performance)
• Highly modular structure
– Each system function is managed by just one component of
the OS: the rest of the OS and all applications access that
component using a standard interface
– Key system data can only be accessed through the
appropriate function
– Any module can be removed, upgraded, or replaced without
rewriting the entire system
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OS Organization – Layered Structure
• Hardware Abstraction Layer (HAL): Maps between generic hardware
commands and responses and those unique to a specific platform
• Microkernel: Consists of the most used and most fundamental components of
the OS. Manages thread scheduling, process switching, exception and
interrupt handling, and multiprocessor synchronization. It does not run in
threads: not preemptable nor pageable
• Device Drivers: File system and hardware device drivers that translate user
I/O function calls into specific hardware device I/O requests
• I/O Manager: Dispatches requests to appropriate device drivers
• Object Manager: Creates, manages, and deletes Executive objects
• Security reference monitor: Enforces access-validation and audit-generation
rules
• Process/thread manager: Creates/deletes objects and tracks process and thread
objects
• Local Procedure Call (LPC) Facility: Enforces client/server relationship
between applications and executive subsystems within a single system
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OS Organization – Layered Structure Cont.)
• Virtual memory manager: Maps virtual addresses in process’s address space
to physical pages in memory
• Cache manager: Improves performance of file-based I/O (read from cache,
defer write)
• Windows/graphics modules: Creates the windows-oriented screen interface
and manages the graphics devices
• User processes:
– Special system support processes: Services not included in W2K (e.g.,
logon process)
– Server processes: Other W2K services (e.g., event logger)
– Environment subsystems: Supported subsystems are Win32, Posix, and
OS/2
– User applications: Can be of five types Win32, Posix, OS/2, Windows 3.1
or MS-DOS
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Client/Server Model
• Operation:
– A client (e.g., application program or another OS module) requests a
service by sending a message
– Message routed through the Executive to appropriate server
– Server performs requested operation and returns results or status with
another message
– Message routed through Executive back to client
• Advantages of client/server architecture:
–
–
–
–
Simplifies the Executive: possible to construct a variety of APIs
Improves reliability: clients cannot not directly access hardware
Provides a uniform means fro applications to communicate via LPC
Provides base for distributed computing
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Threads and SMP
• W2K features that support threads and SMP:
– OS routines can run on any available processor and different
routines can execute simultaneously on different processors
– Multiple threads of execution within a single process may
execute on different processors simultaneously
– Server processes may use multiple threads to process
requests from many clients simultaneously
– W2K provides mechanisms for sharing data and resources
between processes and flexible interprocess communication
capabilities
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UNIX
• Brief history (cont.)
– First widely available version outside Bell Labs was Version 6, in 1976
– Version 7, released in in 1978, is the ancestor of modern UNIX systems
– Most important non-AT&T development done at U. of C. at Berkeley,
called UNIX BSD, running first on PDP, then VAX
– In 1982, Bell Labs combined several AT&T versions into a system
marketed as UNIX System III
– A number of new features were developed to produce UNIX System V
– Traditional UNIX systems: System V Release 3 (SVR3), 4.3BSD
• Traditional UNIX system characteristics:
– Hardware is surrounded by the operating-system called kernel
– UNIX comes with a number of user services and interfaces (I.e., shell,
other interface software, and the components of the C compiler)
– Runs on a single processor and has limited protection capabilities
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UNIX
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Modern UNIX Systems
• System V Release 4 (SVR4)
– Developed jointly by AT&T and Sun Microsystems, combined features
from SVR3, 4.3BSD, Microsoft Xenix System V, and SunOS
– New features: real-time processing support, process scheduling classes,
dynamically allocated data structures, virtual memory management,
virtual file system, and a preemptive kernel
– Runs on machines ranging from 32-bit microprocessors up to
supercomputers
• Solaris 2.x
– Sun’s SVR4-based UNIX release
– Provides a number of advanced features: fully preemptable, multithreaded
kernel, full support for SMP, and an object-oriented interface to file
systems
– Is is the most widely used and most successful commercial UNIX
implementation
• 4.4BSD
• Linux
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Modern UNIX Systems (Cont.)
• 4.4BSD
– Berkeley Software Distribution (BSD) series of UNIX
releases has played a key role in the development of OS
theory
– Most enhancements to UNIX first appeared in BSD versions
– 4.xBSD is widely used in academic installations and has
served as the basis of a number of commercial UNIX
products
– 4.4BSD is the final version of BSD to be released by
Berkeley and includes a new virtual memory system and
changes in the kernel structure
• Linux
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Modern UNIX Systems (Cont.)
• Linux
– Started as a UNIX variant for the IBM PC architecture written by Linus
Torvalds and posted on Internet in 1991
– A large number of collaborators contributed to the development of Linux
under the control of Torvalds
– Linux is free and the source code is available under the auspices of the
Free Software Foundation (FSF)
– Today, Linux is a full-featured UNIX system running on a variety of
platforms
– Linux key advantages:
• Modular structure: kernel organized as a collection of loadable
modules; a module can be loaded and linked into the kernel while the
kernel is in memory and executing
• With source code available, vendors can tweak applications and
utilities to meet specific requirements
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