Operating Systems 1 (2/12) - Hardware Basics

Hardware Basics

Beuth HochschuleSummer Term 2014

Operating Systems I PT / FF 14

Computer Systems Today

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Classes of Operating Systems• Desktop / Server Operating Systems

• Distributed Operating Systems

• Implements a single operating system instance spanning multiple machines

• Applications have single memory space view

• No significant real-world adoption, mainly research topic

• Real-Time Operating System (RTOS)

• Deterministic timing behavior of operating system services

• Support for real-time application scheduling and resource management

• Wide adoption for industry applications

• Examples: LynxOS, OSE, QNX, RTLinux, VxWorks

• Embedded Operating System�3


Main Concepts• Processes

• Process table, core image, fork, command interpreter, shell, child processes, scheduling, signals, user authorization, group identification, process tree, ...

• Memory

• Swapping, paging, segmentation, virtual address, security, device access, ...

• I/O

• Files, directories, root directory, working directory, path, protection, rwx bits, file descriptor, handle, special files, I/O devices, block I/O, character I/O, standard input/output/error, pipes, mailslots, sockets, ...

• ... all abstracting hardware concepts to some extend�4

Main Concepts:Main Concepts: pprorocecessessess

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Main Concepts:Main Concepts: pprorocecessessess

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Main Concepts:Main Concepts: FilesFiles

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File descriptor, handleFile descriptor, handleSpecial files, I/O devicesSpecial files, I/O devicesBlock I/O, character I/OBlock I/O, character I/OStandard input/output/errorStandard input/output/errorpipespipes

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Hardware Basics

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Hardware Basics

• Central Processing Units (CPUs) + volatile memory + I/O devices

• Fetch instruction and execute it - typically memory access, computation, and / or I/O

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(C) Stallings

• I/O devices and memory controller may interrupt the instruction processing

• Improve processor utilization by asynchronous operations


Hardware Basics• Symmetric Multi-Processing (SMP)

• Two or more processors in one system, can perform the same operations (symmetric)

• Processors share the same main memory and all devices

• Increased performance and scalability for multi-tasking

• No master, any processor can cause another to reschedule

• Multi-Core / many-core processor combines computational cores on one chip with shared caches

• Challenges for an SMP operating system:

• Reentrant kernel, scheduling policies, synchronization, memory re-use, ...�7

(C) Stallings


Hardware Basics

• Multi-Programming vs. multi-processing

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Hardware Basics

• Hyperthreading

• Make a single processor appear to be two virtual processors by maintaining separate CPU states, while execution engine and caches are still shared

• Also called Simultaneous multithreading (SMT)

• Operating systems must consider them separately in scheduling (in Windows since XP)

�9

(C) Intel


Hardware Basics

• Parallelism

• Inside the processor (instruction-level parallelism, multicore)

• Through multiple processors in one machine (multiprocessing)

• Through multiple machines (multicomputer)

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Figure 1: Hardware parallelism hierarchy

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Hardware Basics

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Intel Core i7SPARC64™ VIIIfx All Rights Reserved,Copyright© FUJITSU LIMITED 200912

SPARC64™ VIIIfx Chip Overview• Architecture Features

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Hardware Basics

• NUMA (non uniform memory architecture) systems

• Groups of physical processors (called “nodes”) that have local memory

• Connected to the larger system through a cache-coherent interconnect bus

• Still an SMP system (e.g. any processor can access all of memory),but node-local memory is faster

• Operating system tries to schedule close activities on the same node

• Became the default model in all recent architectures

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Hardware Basics

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Hardware Basics

• Major constraints in memory as a resource are amount, speed, and costs

• Faster access time results in greater costs per bit

• Greater capacity results in smaller costs per bit

• Greater capacity results in slower access

• Idea: Going down a memory hierarchy

• Decreasing costs per bit

• Increasing capacity for fixed costs

• Increasing access time

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Hardware Basics

• Principle of Locality

• Memory referenced by a processor (program and data) tends to cluster

• Iterative loops and subroutines, small set of instructions inside

• Operations on tables and arrays involve access to clustered data sets

• Data should be organized so that the percentage of accesses to lower levels is substantially less than to the level above

• Typically implemented by caching concept

• I/O devices provide non-volatile memoryon lower levels, which is an additional advantage

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Hardware Basics

• Caching

• Offer a portion of lower level memory as copy in the faster smaller memory

• Leverages the principle of locality

• Processor caches work in hardware, but must be considered by an operating system

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(C) Stallings


Hardware Basics

• Conflicting caching design goals

• Cache size per level

• Number of cache levels

• Block size exchanged withlower level memory

• Replacement algorithm

• Mapping function

• Write policy for modified cache lines

• All decisions made by hardwarevendor, considerable by software

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(C) Stallings


Hardware Basics

• All computers have mechanisms to let I/O and memory modules interrupt the current processor work

• Consider the speed aspect of I/O devices in the memory hierarchy

• Different classes of interrupt

• Program interrupt: Condition from program execution leads to exceptional situation, such as arithmetic overflow, division by zero, illegal instruction

• Timer interrupt: Programmed hardware time signals the time event,e.g. for regular operating system activities

• I/O interrupt: Generated by any kind of hardware unit to signal I/O completion or an error condition

• Hardware failure interrupt: Hardware module signals permanent issue

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Hardware Basics

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• I/O program prepares an I/O operation, waits for finalization and prepares the result for further processing

• Usage of interrupts reduces the application I/O wait time to the pre- and post phases of I/O processing

• Interrupt can occur at any point in the execution of the user program, must be managed by the operating system


Hardware Basics

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Hardware Basics

• Summary

• Modern operating systems have to deal with many execution units (cores) and processors (SMP) in the same box

• Memory is organized in a deep hierarchy

• Differences in speed and amount at the order of magnitudes

• Devices and other sources can interrupt the current processing at any point

• All of this is permanently changing

• New processors, memory technology, hardware devices, ...

• Operating system must allow applications to use old and new hardware

• Example: Windows Vista supports approx. 4200 printers out of the box

�21

Any problem in computer science can be solved with another layer of indirection.

But that usually will create another problem.

David Wheeler

Date post:	12-Jul-2015
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Operating Systems 1 (2/12) - Hardware Basics

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