Operating Systems: History, Hardware

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Operating SystemsHistory, Hardware Concepts

• Ch 1.4 1.5
• Thursday, January 18, 2007

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Todays Schedule

• Sec 1.4 - Hardware Review
• Sec 1.5 - O/S Concepts
• Quiz 1

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Computer Hardware Review
Monitor
Bus

• Components of a simple personal computer

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Computer Hardware Review

• (a) A three-stage pipeline
• (b) A superscalar CPU

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Processors

• Brain of the computer
• Fetch, decode, execute cycle
• Registers
• Program Counter (PC)
• Stack Pointer (SP)
• Pipelining improves performance, but complexities
  of rolling back appear
• Kernel vs. User Mode (enables establishing
  limitations of instruction set available)

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Computer Memory

• The CPU is often referred to as the brain of the
  computer. This is where all the actual computing
  is done.
• The chipset supports the CPU. It usually contains
  several "controllers" which govern how
  information travels between the processor and
  other components in the system. Some systems have
  more than one chipset.

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Computer Memory

• The memory controller is part of the chipset, and
  this controller establishes the information flow
  between memory and the CPU.
• A bus is a data path in a computer, consisting of
  various parallel wires to which the CPU, memory,
  and all input/output devices are connected.
• The memory bus runs from the memory controller to
  the computer's memory sockets

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Computer Memory

• Memory speed is sometimes measured in Megahertz
  (MHz), or in terms of access time - the actual
  time required to deliver data - measured in
  nanoseconds (ns).
• A computer's system clock resides on the
  motherboard. It sends out a signal to all other
  computer components in rhythm, like a metronome.
• Cache memory is a relatively small amount
  (normally less than 1MB) of high speed memory
  that resides very close to the CPU. Cache memory
  is designed to supply the CPU with the most
  frequently requested data and instructions.

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Memory Tradeoff - Speed vs. Capacity
For RAM, how many bytes in 1KB? In 1 MB? 1000
and 1,000,000? NO!

• Typical memory hierarchy
• numbers shown are rough approximations

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Multiple Processes in Memory

• One base-limit pair and two base-limit
  pairsProtection and Relocation problems solved!

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Memory Allocation

• We need a protective and fair way of allocating
  and resizing memory blocks for processes/jobs
• Two sections of memory
• Code (typically static)
• Data (volatile)

Limit
User 2 Data
Base
Limit
User 1 Data
Base
Limit
Program Code
Base
OS
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Memory Management Unit (MMU)

• Device that checks and maps memory addresses
• Virtual Address address generated by the
  program
• Physical Address address actually used in memory

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I/O Devices

• Typically consist of two parts
• Controller
• Device
• Controller manages presents the API of the
  device to the OS
• The software that talks to the controller is
  called a device driver

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Input and Output

• Busy Waiting
• User issues system call, driver waits in loop
• Ties up CPU polling device
• Interrupt
• Driver starts device, requests interrupt when
  finished
• CPU looks for other work, until interrupt
  received
• Direct Memory Access (DMA)
• Chip controls flow of bits memory and controller
• CPU not constantly involved

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I/O Devices
(a)

• Steps in starting an I/O device and getting
  interrupt
• How the CPU is interrupted

(b)
Where does the Interrupt Handler store its data?
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Bus

• Communication highway for all data to travel
  upon
• Multiple buses exist in modern machines
• Cache (fastest)
• Local (on mainboard other busses connect to it)
• Memory
• PCI (successor of ISA - high-speed I/O)
• SCSI (high-speed scanners disks)
• USB (slow peripherals)
• IDE (disks, etc.)
• ISA (slowest legacy)

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Buses in PC

• Structure of a large Pentium system

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OS Concepts

• Processes
• Deadlock
• Memory Management
• I/O
• Files
• Security

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Processes

• Defined as a program in execution
• AKA a job
• Contain
• Instructions (code segment)
• SP, PC, registers, file handles
• Data segment
• Processes can spawn subprocesses threads
• The OS must ensure fairness protection,
  timeslicing managing multiple processes at a
  time

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Deadlock

• Two or more processes stalemated because they
  cant make progress

Process A Has resource 1 Waiting on resource 2
Process B Has resource 2 Waiting on resource 1
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Memory Management

• Providing protection of one process memory
  section from another process (security)
• Providing a fair allocation of memory to multiple
  processes
• Swapping memory to disk as needed

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Input/Output

• All OS must manage I/O devices
• Two categories
• Device independent
• Device dependent (device drivers)

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Files

• System calls
• Create, remove, read, write, etc.
• Directories subdirectories
• Create, remove, rename, move, etc.

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Security

• Allocate permissions
• Directories
• Files
• Example UNIX policies to consider
• Read, Write, Execute
• User, Group, World

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System Calls

• Services that the OS provides to the user
• Set of API that user-level programs may invoke
• Flavors of System Calls
• UNIX
• Win32

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UNIX System Calls

• pid fork() creates child process
• exit() terminates process
• fd open(file, ) opens file
• s mkdir(name, mode) creates directory
• s chmod(name, mode) sets file/dir permissions
• s kill(pid, signal) sends signal to process

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Win32 System Calls

• CreateProcess() creates new process
• ExitProcess() terminates process
• CreateFile() opens file
• CreateDirectory() creates directory

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Approaches to OS

• Monolithic
• Virtual Machines
• Client-Server (microkernel)

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Monolithic OS Architecture

• OS written as a set of procedures
• Each procedure has well-defined interface
  (parameters)
• Very little structure or information hiding

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Virtual Machine OS Architecture

• Replicate the hardware within software
• Trap OS calls and translate/handle them
• Breaks down if you make direct I/O calls
• Slow(Windows running DOS applications)
• Other approach JVM (define an alternate
  instruction set and translate to various OS)

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Client-Server OS Architecture

• Implement as much as possible in user-level
  modules
• The OS is as small as possible
• It only serves to translate and message pass
  OS-level calls to service processes

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Tuesday, January 23

• Read Chapter 2 - Processes and Threads Sections
  2.1 2.2.2 (ends top pg 90)
• Do not worry about code fragments, reading for
  understanding
• concept of process
• Process states
• Threads and why they are useful