Download 1.2. OS Introduction Computer System types

Computer System types and description
Desktop Computer Systems
• The goals of the operating systems have changed with time
• Instead of maximizing CPU and peripheral utilization, the systems opt
for maximizing user convenience and responsiveness.
• With improvement of chip technology the processors and computing
power resources became cheaper.
• Then appear real possibilities to create user friendly operating
systems.
Old Desktop OS
Intermed. Desktop OS
New Desktop OS
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No protection
Single User
Single Task
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DOS
Windows <=3.11
 Windows 95,98,ME
(not fully multi user)
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No protection
Multi User(not full)
Multitasking
Microsoft OS improves
Protection and Security
Multi User
Multitasking
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Windows NT
Windows 2000
Windows XP
Vista
Windows 7
Computer System types and description
Single Processor Systems
• On a single processor system, there is one main CPU capable of
executing a general-purpose instruction set, including instructions
from user processes.
• Almost all single processor systems have other special-purpose
processors as well.
• All of these special-purpose processors run a limited
instruction set and do not run user processes.
• It is very effective to add a microprocessor with its own
memory to manage a disk system thus significantly
reducing the load of the main CPU.
• Additional processor can function as: HDD Controller,
Keyboard Controller . . . other controllers.
• In fact, this use of microprocessors has become so
common that it is no longer considered multiprocessing.
Computer System types and description
Tightly Coupled or Multiprocessor Systems
Multiprocessing is implemented connecting the computers to
each other on system bus or other local bus levels.
Multiprocessor systems 3 main advantages:
• Increased throughput (Many processors, many tasks more
volume of calculations)
• Economy of scale (Many tasks on the same data do not need
many computers but one multiprocessor computer)
• Increased reliability (graceful degradation, fault tolerantfailure does not halt the system)
Tightly Coupled or Multiprocessor Systems
Tandem Multiprocessor Systems
Tandem Multiprocessor System Specificities:
 Both hardware and software duplication
 2 identical processors Main and Backup
 Periodical backup (at time checkpoints) of Main CPU state to the Backup CPU.
 In case of Main CPU failure the Backup CPU is activated from the recent checkpoint.
Main (active)
Backup (passive)
CPU
Backup the state at CPU
checkpoints
CPU connection BUS
Disks
Memory
Memory
Disadvantage: This solution is expensive, since it involves considerable
Tandem
Multiprocessor System (Full duplication).
hardware
duplication.
Tightly Coupled or Multiprocessor Systems
Symmetric Multiprocessing Systems
• Parallel running of copies of the same Operating System, with different tasks
• Equal rights to control the system
• Communication each with other
CPU
CPU
System Bus
Memory
Memory
Problems:
Advantage:
• However, we must carefully control I/O to ensure that the data reach the
appropriate
processor
(ifsimultaneously-N
the memories are separate).
• Many
processes
can run
processes can run if there are N
• Also, since the CPUs are separate, one may be sitting idle while another is
CPUs-without causing a significant deterioration of performance.
overloaded, resulting in inefficiencies (data is in wrong memory).
• • NoThese
forever
idle backup processors
inefficiencies can be avoided if the processors share memory dynamically.
SMP system with shared memory
• Processors can access
the same data in
memory without
difficulties.
• The processors are
quite autonomous
because of own
internal caches.
•Problems:
All modern operating systems-including Windows, UNIX, Linux - now provide
forproblem
SMP. remains to take care. Caches partially resolve it.
• support
Shared bus
Tightly Coupled or Multiprocessor Systems
Asymmetric Multiprocessing Systems
• Parallel running of the same or other Operating Systems, with different
tasks (belonging to user processes)
• Not Equal rights to control the system
• Communication each with other
Master
CPU
Memory
Slave CPU(s)
Memory
Asymmetric Multiprocessing
• A master processor controls the system;
• The other processors either look to the master for instruction or have
predefined tasks.
MultiCore
 A recent trend in CPU design is to include multiple computing cores on a
single chip.
 Such multiprocessor systems are termed multicore.
 They can be more efficient than multiple chips with single cores because
on-chip communication is faster than between-chip communication.
 In addition, one chip with multiple cores uses significantly less power
than multiple single-core chips.
 In this design, each core has
 its own register set
 as well as its own local cache.
 Other designs might use
 a shared cache
 or a combination of local and
shared caches.
Hyper-threading
Hyper-threading works by duplicating certain sections of the processor
 those that store the architectural state
 but not duplicating the main execution resources.
 This allows a hyper-threading processor to appear
 as the usual "physical" processor
 and an extra "logical" processor to the host operating system
The architectural state is the part of the CPU which holds the state of a process,
this includes:
Control registers
• Instruction Flag Registers (such
as EFLAGS in x86)
• Interrupt Mask Registers
• Memory management unit
Registers
• Status registers
• Thread Context switch time is reduced
• Almost parallel running of threads
General purpose registers (such as
AX,BX,CX,DX,etc. in x86)
• Adder Registers
• Address Registers
• Counter Registers
• Index Registers
• Stack Registers
• String Registers
Loosely Coupled or Distributed Systems
 Unlike Multiprocessing the Loosely Coupled systems are connected
to each other through device controllers, devices and
communication lines.
 Thus these connections are slower than tightly coupled connections.
Computer 1
Computer 2
System Bus
Network Card
Communication Lines
Buses
Wires
Fiber Optics
Wireless
Network Card
Loosely Coupled or Distributed Systems
A network is a communication path between two or more systems.
A distributed system is a collection of physically separate, possibly
heterogeneous, computer systems that are networked to provide the users
with access to the various resources that the system maintains.
LAN1
City1
City2
WAN
LAN3
Node ?
Room1, Bulding1
MAN
LAN2
LAN1
Room2, Bulding1
Rest of the
processors and
their respective
resources are
remote
Room in Bulding2
Host
Room in Bulding3
Site
Own resources are local
Loosely Coupled or Distributed Systems
Networks are classified based on the distances between their nodes.
• A local-area network (LAN), exists within a room, a floor, or a building.
• A wide-area network (WAN), usually exists between buildings, cities, or
countries.
• A metropolitan-area network (MAN), could link buildings within a city.
LAN1
City1
City2
WAN
LAN3
Room1, Bulding1
LAN1
MAN
LAN2
Room in Bulding2
Room2, Bulding1
Host
Room in Bulding3
Site
Loosely Coupled or Distributed Systems
To an operating system, a network protocol simply needs an
interface device
 a network adapter
 with a device driver - to manage it
 software - to package data in the communications protocol to
send it and to unpackage to receive it.
Netowork
Application
Programs
API Interface to OS for User Applications
Operating System
Device drivers
Control API to Hardware
Network Adapter
LAN card, Wireless card
Loosely Coupled or Distributed Systems
Client - Server Systems
compute-server system
• The
a client
can sendfunctionality
a request to
perform
(for
example,
read data).
user-interface
that
used toan
beaction
handled
directly
by the
Server
systems
can
beisbroadly
categorized
as compute
servers
and file
• centralized
In response
to
which,
the server
executes
the action
and
theservers.
results
systems
increasingly
being
handled
by the
PCs.sends
to
the client.
File-Server
systemssystems
- usualtoday
file sharing
As
a result, centralized
act as server systems to satisfy requests
• A server running a database that responds to client requests for data is an
generated by client systems.
Compute-Server
systems
example of such
a system.- Remote Terminal, Application Servers.
file-server system
• clients can create, update, read, and delete files on the server.
•
An example of such a system is a web server that delivers files to clients running
PC
PC
PC
PC
web browsers.
The general structure of a client-server system.
Peer-to-Peer Systems
• Peer to Peer system is a distributed network with autonomous hosts.
• Each processor has its own local memory
• Hosts are interconnected by a communication network.
• Purpose: To provide resource sharing via communication network (with equal
rights)
• The servers are “bottleneck”?
Host1
Host3
Network
Host2
Host4
• All nodes within the Peer to Peer system are considered peers
• Clients and servers are not distinguished from one another
• Each may act as either a client or a server, depending on whether it is
requesting or providing a service.
Loosely Coupled or Distributed Systems
Clustered Systems
This is multiprocessing through LAN.
Formal Definition: clustered computers are autonomous hosts sharing some
resources (like storage) and are closely linked via LAN networking.
Host1
Host3
LAN
Host2
Host4
Memory
The same advantages as for multiprocessing:
• Increased throughput (Many processors, many tasks more volume of calculations)
• Economy of scale (No need to have large memory on each host)
• Increased reliability (graceful degradation, fault tolerant- failure does not halt the
system)
Asymmetric clustering
Host1
Host3
Loaded
LAN
Host2
Host4
Memory
Idle
Asymmetric clustering: one machine is in hot standby mode while the other is
running the applications. The hot standby host (machine) does nothing but
monitor the active server. If that server fails, the hot standby host becomes the
active server.
Disadvantage: One of the hosts all the time is idle.
Symmetric clustering
Host1
Host3
Loaded
LAN
Host2
Host4
Memory
Loaded
Symmetric clustering: Two or more hosts are running applications, and they
monitor each other.
Advantage: Both are loaded.
Problem: It does require that more than one application be available to run to
keep busy both hosts.
Clustered Systems - SAN
• Clustered system use and features should expand greatly as storage-area
networks (SAN) become prevalent.
• SANs allow easy attachment of multiple hosts to multiple storage units
thus increasing the reliability of system.
Cloud Computing
Cloud computing is a type of computing that delivers
computing, storage, and even applications as a service across
a network:
 Public cloud—a cloud available via the Internet to anyone
willing to pay for the services
 Private cloud—a cloud run by a company for that company’s
own use
 Hybrid cloud—a cloud that includes both public and private
cloud components
Cloud Computing
 Software as a service (SaaS)—one or more applications (such as
word processors or spreadsheets) available via the Internet
 Platform as a service (PaaS)—a software stack ready for application
use via the Internet (for example, a database server)
 Infrastructure as a service (IaaS)—servers or storage available over
the Internet (for example, storage available for making backup
copies of production data)
 Ransomware as a service? 
a public cloud providing IaaS
Real Time Systems
Requirements: A real-time system has well-defined, fixed time constraints.
Processing must be done within the defined constraints, or the system will
fail.
Flavors: hard and soft
Hard: A hard real-time system guarantees that critical tasks be completed on
time.
Soft: critical real-time task gets priority over other tasks, and retains that
priority until it completes
Real-Time Systems usage areas:
 scientific experiments
 medical imaging systems
 industrial control systems (nuclear power plant)
 automobile-engine fuel-injection systems
 home-appliance controllers
 weapon systems
 encryption / decryption systems
Handheld Systems
Handheld Systems usage areas:
In very small size devices
Palm Pilots
Tablets
Cellular phones
Requirements: small size dictates:
small amount of memory
small display
less powerful processor to consume less energy