University of Pennsylvania
9/7/00
Insup Lee
Fall 00
CSE 380 1

University of Pennsylvania
• A piece of software that provides a convenient, efficient environment for the execution of user programs.
Users
Applications software
Systems software
Operating systems
Hardware
9/7/00 CSE 380 2

University of Pennsylvania
• Hides the details of how the hardware operates
• Provides an abstract model of the operation of hardware components
– generalize hardware behavior
– limit the flexibility in which hardware can be manipulated
• Computation model: processes, threads
• Resources: memory, disk, files, cpu, etc.
9/7/00 CSE 380 3

University of Pennsylvania
• User viewpoint -- provide user interface, command interpreter, directory structure, utility programs
(compilers, editors, filters)
• Program environment viewpoint -- enhance the bare machine higher-level I/O, structure files, notion of independent processes, improved store (size, protection)
• Efficiency viewpoint -- replace a human operator scheduling jobs, storing I/O (files), invoking necessary programs such as compiler
• Economic viewpoint -- allow concurrent uses and good scheduling of resources
So, the goals are to make the system convenient to use (via system calls) and to manage resources efficiently.
9/7/00 CSE 380 4

• Hardware upgrades
• New types of hardware
• New services
• Fixes
University of Pennsylvania
5 9/7/00 CSE 380

University of Pennsylvania
• 1940's -- First Computers
• 1950's -- Batch Processing
• 1960's -- Multiprogramming (timesharing)
• 1970's -- Minicomputers & Microprocessors
• Late 1970's, 1980's -- Networking, Distributed
Systems, Parallel Systems
• 1990's and Beyond -- PC’s, WWW, Mobile Systems
9/7/00 CSE 380 6

University of Pennsylvania
• Computer dedicated to one user/programmer at a time.
Program loaded manually by programmer, using console switches. Debugging using console lights.
• Advantages:
– Interactive (user gets immediate response)
• Disadvantages:
– Expensive machine idle most of time, because people are slow.
– Programming & debugging are tedious.
– Each program must include code to operate peripherals -error prone, device dependencies.
• Libraries of subroutines to drive peripherals are example of typical OS service.
9/7/00 CSE 380 7

University of Pennsylvania
• User/programmer submits a deck of cards that describes a job to be executed.
• Jobs submitted by various users are sequenced automatically by a resident monitor.
• Tape drives available for batching of input and spooling of output.
• Advantages:
– Computer system is kept busier.
• Disadvantages:
– No longer interactive; longer turnaround time.
– CPU is still idle for I/O-bound jobs.
• OS issues -- command processor (JCL), protection of resident monitor from user programs, loading of user programs after monitor.
9/7/00 CSE 380 8

University of Pennsylvania
• The advent of the I/O processor made simultaneous I/O and CPU processing possible.
• CPU is multiplexed (shared) among a number of jobs -- while one job waiting for I/O, another can use CPU.
• Advantages:
– Interactiveness is restored.
– CPU is kept busy.
• Disadvantages:
– Hardware and O.S. required become significantly more complex.
• Timesharing - switch CPU among jobs for pre-defined time interval
• Most O.S. issues arise from trying to support multiprogramming --
CPU scheduling, deadlock, protection, memory management, virtual memory, etc.
• CTSS (Compatible Time Sharing System), Multics
9/7/00 CSE 380 9

University of Pennsylvania
• Trend toward many small to mid-range personal computers, rather than a single mainframe.
• Early minicomputers and microprocessors were small, so there was some regression to earlier OS ideas.
– e.g. DOS on PC is still essentially a batch system similar to those used in 1960, with some modern OS ideas thrown in (e.g., hierarchical file system).
• This trend is changing rapidly because of powerful new microprocessors.
• Also, the user interface became more important.
• UNIX, DOS
9/7/00 CSE 380 10

University of Pennsylvania
• Powerful workstations (e.g., PDP, VAX, Sunstations, etc.)
• Local area networks (e.g., Ethernet, Token ring) and longdistance network (Arpanet)
• Networks organized with clients and servers
• Decentralization of computing requires more communication
(e.g., resource sharing)
• O.S. issues -- network communication protocols, data encryption, security, reliability, consistency of distributed data
• Real-Time Systems – timing constraints, deadlines, QoS
(90’s term)
9/7/00 CSE 380 11

University of Pennsylvania
• Parallel Computing (tera-flops)
• Powerful PCs, Multimedia computers
• High-speed, long-distance communication links to send large amounts of data, including graphical, audio and video
• World Wide Web
• Electronic notebooks using wireless communication technologies
• O.S. issues -- Large heterogeneous systems, mobile computing, etc.
9/7/00 CSE 380 12

University of Pennsylvania
• Processes: programs in execution
• Resources (e.g., files, memory, display)
– A process must request it from the OS
– The process is blocked until it is allocated
• System calls
• Shell -- command interpreter
9/7/00 CSE 380 13

University of Pennsylvania
• Program creation
• Program execution
• Access to I/O devices
• Controlled access to files
• Error detection and response
– hardware errors (e.g., memory error, device failures)
– software errors (e.g., overflow, out of memory boundary)
• Accounting
– collect usage statistics, monitor performance
9/7/00 CSE 380 14

University of Pennsylvania
• CPU scheduling: allocate computing time among several processes
• Memory management: allocate main memory among several processes
• Swapping: move processes and their data between main memory and secondary storage
• I/O device drivers: specialized code required to operate I/O devices
• File system: organize mass storage (disk) into files and directories
• Utilities: date/time, accounting, file copy, etc.
• Command interpreter: allow users to enter commands interactively
• System calls: allow user programs access to O.S. services
• Protection: keep processes from interfering with each other and system
• Communication & Resource sharing: allow users/processes to communicate (over networks) and share resources (e.g., laser printers, disks, etc.)
• Security: protect machines from intruders, worms and viruses
9/7/00 CSE 380 15

University of Pennsylvania
• Engineering factors:
– Performance/Efficiency -- CPU utilization, resource utilization (e.g. disks), response time
– Correctness/Reliability -- error-free (no software crashes)
– Maintainability -- modular construction, clearly defined interfaces, well-documented
– Small in size-- main memory and secondary storage valuable, larger means more error-prone, larger means takes longer to write
• Non-engineering factors:
– Commercial factors
– Standards and open systems
9/7/00 CSE 380 16

• Monolithic Systems
• Layered Systems
• Virtual Machines
• Client-Server Model
University of Pennsylvania
17 9/7/00 CSE 380