Topic 1 – What is an OS? 1 CS502 Spring 2006 What is an Operating System? Characteristics –Large, complex set of programs –Long-lived, evolutionary –Worked on by many people over many years Functions –Creates abstractions –Multiplexes concurrent activities –Manages resources –Mediates access to hardware devices –Provides a variety of services to users and applications Class Discussion

Topic 1 – What is an OS? 2 CS502 Spring 2006 What is an operating system? (cont’d) Abstractions:– –Implements processes & threads –Implements virtual memory & manages memory –Provides interprocess communication (IPC) –Implements file system. Manages persistent storage of information Controls I/O Implements networking & communications Definition — Same as judicial definition of pornography “I cannot define it, but I sure can recognize one when I see it!”

Topic 1 – What is an OS? 3 CS502 Spring 2006 What is an Operating System Hardware Interfaces – Registers, etc. OS Kernel Prog. ToolsServicesUI/Shell XYZ OfficeMedia PlayerBusiness Appl. CPUI/O Controllers Traditional OS Practical OS

Topic 1 – What is an OS? 4 CS502 Spring 2006 Major OS Issues structure: how is the OS organized? sharing: how are resources shared across users? naming: how are resources named (by users or programs)? security: how is the integrity of the OS and its resources ensured? protection: how is one user/program protected from another? performance: how do we make it all go fast? reliability: what happens if something goes wrong – hardware or software extensibility: can we add new features? communication: how do programs exchange information concurrency: how are parallel activities created and controlled? scale: what happens as demands or resources increase? persistence: how do you make data last longer than program executions? distribution: how do multiple computers interact with each other? accounting: how do we keep track of resource usage, and charge for it?

Topic 1 – What is an OS? 5 CS502 Spring 2006 Operating Systems Large, complex programs Typically –Long-lived –Frequently extended and updated –Worked on by a number of developers –Used and, maybe abused by a variety of users with varying expertise and expectations Essential to create an acceptable computing environment to create and execute other programs that achieve business or personal goals

Topic 1 – What is an OS? 6 CS502 Spring 2006 Kinds of operating systems Stand-alone machines – no OS Simple batch monitors Concurrent I/O and programs Time-sharing, multiple users, interactive Servers, non-stop systems, transaction processing PC’s, workstations Multiple processor systems Real-time systems Embedded systems

Topic 1 – What is an OS? 7 CS502 Spring 2006 Kinds of operating systems (1) Stand-alone machines – no OS Manually scheduled “jobs,” reset between jobs Early business computers –E.g., IBM 1401/1460 Early mini-computers –E.g., PDP1, PDP5, PDP8, etc. Simple batch monitors Simple “monitor routine” switches between jobs Input loaded onto tape off-line Output to tape is punched and/or printed off-line Typical university computing centers –IBM 7090, Univac, etc.

Topic 1 – What is an OS? 8 CS502 Spring 2006 Kinds of operating systems (2) Concurrent I/O and programs SPOOL-ing (Simultaneous Peripheral Operation On Line) –Allows direct input & output Multiple programs resident in memory at once –Keeps processor busy On-line file storage Some support for terminals, telecommunications Early business computers –E.g., IBM 7070, IBM 360 & 370 Scientific computing –E.g., Control Data 6600, IBM 360/91

Topic 1 – What is an OS? 9 CS502 Spring 2006 Kinds of operating systems (3) Time-sharing, multiple users, interactive Many concurrent users “logged on” Interactive editing and computing Self submission of batch jobs Protection among users, protection among jobs Fair allocation of resources All university computing centers since about 1970 –E.g., MULTICS, IBM 360/67, DEC PDP-10, PDP-20 Advanced minicomputers –DEC, Data General, Prime, etc. –Unix

Topic 1 – What is an OS? 10 CS502 Spring 2006 Kinds of operating systems (4) Servers, non-stop systems, transaction processing Banking, airline reservation Online databases Many very short “transactions” Tandem, Stratus, Sequoia Unix, Linux, Solaris, HP-UX Windows Server 2000, 2003 Oracle, SAP (?)

Topic 1 – What is an OS? 11 CS502 Spring 2006 Kinds of operating systems (5) PC’s, workstations CP/M, DOS, MS-DOS Apollo Domain Unix, Solaris, HP-UX Mac OS Windows 95, 98, Me Windows 2000, XP Linux Multiple processor systems Beowulf clusters Unix, Solaris, HP-UX, Linux

Topic 1 – What is an OS? 12 CS502 Spring 2006 Kinds of operating systems (6) Real-time systems SAGE (North American air defense) Process control (steel mills, refineries, etc.) Large and small; computers you never heard of VxWorks, etc. Embedded systems Auto ignition Cell phone, PDA Appliances …

Topic 1 – What is an OS? 13 CS502 Spring 2006 OS History – Unix & Linux Unix –Descendant of Multics –First “C” version in 1973 (DEC PDP-11) Timesharing for < 10 users on 32K Memory Many Unix versions at BTL – different goals Source code made available to Universities – BSD –Posix (start 1981) defines standard Unix system calls –AT&T licensing!

Topic 1 – What is an OS? 14 CS502 Spring 2006 OS History - Linux Open Source – Linux.org First Version 1991, Linus Torvalds, processor –v.01, limited devices, no networking, –with proper Unix process support! 1994, v1.0 –networking (Internet) –enhanced file system –many devices, dynamic kernel modules

Topic 1 – What is an OS? 15 CS502 Spring 2006 OS History - Linux 1996, v2.0 –multiple architectures, multiple processors –threads, memory management …. Gnome UI – introduced in 1999 Recent –V million lines of code –7-10 million users –Growth by 25%/year through 2003 –Growing use in business server market Note - Development convention –Odd numbered minor versions “development” –Even numbered minor versions “stable”

Topic 1 – What is an OS? 16 CS502 Spring 2006 OS History – Windows NT/2000/XP Key designer – David Cutler also designed VAX/VMS 1988, v1 - Win32 API – “microkernel” 1990, v3.1- Server and Workstation versions 1996, v4 –Win95 interface –Graphics to kernel –More NT licenses sold than all Unix combined –Microkernel de-emphasized

Topic 1 – What is an OS? 17 CS502 Spring 2006 OS History – Windows NT/2000/XP Windows 2000 – NT5.0 –Multi-user (with terminal services) –Professional - desktop –Server and Advanced Server - Client-server application servers –Datacenter Server - Up to 32 processors, 64 GB RAM Windows XP –Windows 2000 code base –Revised UI –EOL for DOS/Windows line

Topic 1 – What is an OS? 18 CS502 Spring 2006 OS History – Windows NT/2000/XP Microsoft has 80% to 90% of OS market Wintel – Windows + X86 WinNT 4.x is 12 million lines of code Win2000 is 18 million lines of code

Topic 1 – What is an OS? 19 CS502 Spring 2006 OS and Hardware OS mediates programs’ access to hardware –Computation – CPU –Storage – volatile (memory) and persistent (disk) –Networks – NIC, protocols –I/O devices – sound cards, keyboards, displays OS creates uniform abstractions –Processes –Files –Sockets –Streams