OPERATING SYSTEMS BIT 1003 OUTLINE Introduction concepts review

OPERATING SYSTEMS BIT 1003

OUTLINE Introduction, concepts, review & historical perspective Processes � Synchronization � Scheduling � Deadlock Memory management, address translation, and virtual memory Operating system management of I/O File systems

WHY SHOULD I STUDY OPERATING SYSTEMS? Need to understand interaction between the hardware and applications � New applications, new hardware. . Need to understand basic principles in the design of computer systems � efficient resource management, security, flexibility Increasing need for specialized operating systems � e. g. embedded operating systems for devices - cell phones, sensors and controllers � real-time operating systems - aircraft control, multimedia services

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THE SERVICES OPERATING SYSTEMS PROVIDE INCLUDE: Management of I/O Management of memory Scheduling of user processes (start, interrupt, and stop) A secure and reliable environment for programs and users A convenient interface for users Networking services Messaging and synchronization services between processes Utility “system software” such as editors, loaders, help, etc.

OPERATING SYSTEM TIMELINE First generation: 1945 – 1955 � � Second generation: 1955 – 1965 � � Integrated circuits Multiprogramming Fourth generation: 1980 – present � � Transistors Batch systems Third generation: 1965 – 1980 � � Vacuum tubes Plug boards Large scale integration Personal computers Next generation: ? ? ? � � Systems connected by high-speed networks? Wide area resource management?

FIRST GENERATION: DIRECT INPUT Run one job at a time � Enter it into the computer (might require rewiring!) � Run it � Record the results Problem: lots of wasted computer time! � Computer was idle during first and last steps � Computers were very expensive! Goal: make better use of an expensive commodity: computer time

SECOND GENERATION: BATCH SYSTEMS Bring cards to 1401 Read cards onto input tape Put input tape on 7094 Perform the computation, writing results to output tape Put output tape on 1401, which prints output

THIRD GENERATION: MULTIPROGRAMMING Multiple jobs in memory � Job 3 Job 2 Memory partitions Job 1 Operating system Protected from one another Operating system protected from each job as well Resources (time, hardware) split between jobs Still not interactive User submits job � Computer runs it � User gets results minutes (hours, days) later �

TIMESHARING Multiprogramming allowed several jobs to be active at one time � Initially used for batch systems � Cheaper hardware terminals -> interactive use Computer use got much cheaper and easier � No more “priesthood” � Quick turnaround meant quick fixes for problems

TYPES OF MODERN OPERATING SYSTEMS Mainframe operating systems: MVS Server operating systems: Free. BSD, Solaris Multiprocessor operating systems: Cellular IRIX Personal computer operating systems: Windows, Unix Real-time operating systems: Vx. Works Embedded operating systems Smart card operating systems ÞSome operating systems can fit into more than one category

MANAGEMENT OF INPUT AND OUTPUT Outside world Video controller CPU Memory Hard drive controller USB controller Network controller Computer internals (inside the “box”)

ANATOMY OF A DEVICE REQUEST (INTERRUPT) 3 CPU 1 5 Interrupt controller 6 2 1: Interrupt Disk controller 4 Instructionn+1 Operating system 3: Return Interrupt handler 2: Process interrupt Left: sequence as seen by hardware Request sent to controller, then to disk � Disk responds, signals disk controller which tells interrupt controller � Interrupt controller notifies CPU � Right: interrupt handling (software point of view)

DIRECT MEMORY ACCESS A improvement in efficiency is possible when the I/O device is relatively fast, like a disk drive or a tape drive. The computer design may include one or more direct memory access (DMA) controllers (or channels). A DMA controller is a computer within the computer that specializes in I/O, and its purpose is to drastically reduce the number of interrupts that the OS must service.

MEMORY MANAGEMENT The operating system is responsible for assigning to processes memory in which to execute. Operating system is responsible for managing a whole array of memories in support of processes, principally main memory, cache memory, and disk memory.

STORAGE PYRAMID Capacity Better Access latency < 1 KB Registers 1 ns 1 MB Cache (SRAM) 2– 5 ns 256 MB Main memory (DRAM) 50 ns 40 GB Magnetic disk 5 ms > 1 TB Magnetic tape 50 sec Goal: really large memory with very low latency Latencies are smaller at the top of the hierarchy � Capacities are larger at the bottom of the hierarchy � Solution: move data between levels to create illusion of large memory with low latency Better

DISK DRIVE STRUCTURE Data stored on surfaces Up to two surfaces per platter � One or more platters per disk � Data in concentric tracks � Tracks broken into sectors � 256 B-1 KB per sector Cylinder: corresponding tracks on all surfaces Data read and written by heads Actuator moves heads � Heads move in unison head sector platter track cylinder surfaces � spindle actuator 17

MEMORY Address 0 x 2 ffff 0 x 2 b 000 0 x 27 fff 0 x 23000 Address User program and data 0 x 1 dfff Limit 0 x 2 ffff 0 x 2 d 000 User data 0 x 2 bfff 0 x 29000 User data 0 x 24 fff Base 0 x 23000 Limit 1 Base 1 0 x 1 dfff Operating system 0 User program Limit 2 Base 2 Operating system 0 Single base/limit pair: set for each process Two base/limit registers: one for program, one for data 18

OPERATING SYSTEMS CONCEPTS Processes (and trees of processes) Deadlock File systems & directory trees Pipes

PROCESSES Address space (memory) the program can use � State (registers, including program counter & stack pointer) � A B C D E Process: program in execution F G OS keeps track of all processes in a process table Processes can create other processes � � � Process tree tracks these relationships A is the root of the tree A created three child processes: B, C, and D C created two child processes: E and F D created one child process: G

DEADLOCK Potential deadlock Actual deadlock

HIERARCHICAL FILE SYSTEMS

INTERPROCESS COMMUNICATION Processes want to exchange information with each other Many ways to do this, including Network � Pipe (special file): A writes into pipe, and B reads from it � A B 23

EXERCISES 6. 1, 6. 2, 6. 4