1 types of processors
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Classification Based On Number
Of Processors
1. Single Processor Systems
2. Multiprocessor Systems3. Clustered Systems
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Single Processor Systems
One CPU present. Most commonly found, frommainframes to laptops.
special purpose processors may be present like:-
Math processor
Disk processor
Keyboard processor
Video processor
Audio processorI/O processor
Co-processor
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Multi Processor Systems
(Parallel or Tightly Coupled)
Have 2 or more General Purpose Processors in close
communication.
Normally the processors share the computer bus,
clock, memory and peripheral devices. Are of importance and are increasing in number.
Are much costlier but have 3 major advantages :-
1. Increased throughput2. Economy of scale
3. Increased reliability
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Increased throughput
Throughputis the amount of work that a
computer can do in a given time period.
Howeverspeed up ratio is not equal to N but a little
lesser, where N is the no. of processors (because the
bus, memory, peripheral devices are shared).
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Economy of scale
Works out cheaper or there is economy with scalingof processors.
Compare multipleSingle Processor System with a
singleMulti Processor System. Which costs lesser ?And Why?
1. They share power supplies
2. They share peripherals
3. They share mass storage4. If several programs ar operating on the same data
just one copy of the data is sufficient.
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Increased reliability
Failure of one processor need not halt the system. The
other processors can take up the work to completion.
Such systems are termed fault tolerantor systems
with graceful degradation
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Fault Tolerant
even if a processor or a component fails, the
operation of the system is not hindered.
faults are detected, diagonised and if possible
corrected too.Eg:- TheHP non-stop system or theHP tandem system
it uses both hardware and software duplication to
ensure continued operations. It has multiple pairs of CPUs which work in lock
step.
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Lock Step
A pair of processors will execute the same instructions
and will compare the results.
If there is a mismatch it means one CPU is corrupt.
Immediately both are halted. The executing process is carried out by another pair of
processors.
( is an expensive solution)
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Graceful Degradation
The ability to provide service proportional to the level
of surviving hardware is called graceful degradation.
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Types Of Multiprocessors
2 kinds namely symmetric and asymmetric
multiprocessors.
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Symmetric Multiprocessors
Are more common.
All CPUs are like peers.
If nprocessors present, nprocesses can getexecuted in true parallel way.
Eg:- Sun Solaris operating system.(it can beconfigured to employ dozens of processors all running
Solaris.)
What care has to be taken in SMS?
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Sophisticated I/O control is required to ensure that the
right data reaches the right processor.
Disparity among the processors to be minimised i.e.
one sitting idle and the other unduly gettingoverloaded.
Note:-All modern operating systems including
Windows, Windows XP, Mac OS X, and Linux
support SMP.
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Asymmetric Processors
Here each processor is assigned a distinct task.
A master processor controls all others.
The relationship amongst the processors is master-
slave.
The master processor schedules and allocates work to
the slaves.
Eg:- Sun OS (version 4) provided asymmetric
multiprocessing.
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Recent Trends in CPU design
Dual core processors and multicoreprocessors.
They are found in fast higher ended machines.
All the core cpus are kept in the same chip.
They look like n standard processors to the o.s.
Blade servers are a recent development. Their web
definition is here:-
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A blade server is essentially a housing for
a number of individual minimally-packaged
computer motherboard "blades", each
including one or more processors,memory, storage, and network
connections, but sharing the common
power supply and air-cooling resources ofthe chassis.
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Definition ofblade PC
A PC architecture that houses multiple PCmodules ("blades") in a single chassis.
It takes the machines off the users' desks and
houses them in rack mounted cabinets in thedatacenter similar to blade servers.
The user's keyboard, monitor and mouse pluginto a device at the desk that is wired via a
TCP/IP or direct connection to the assignedblade in the datacenter.
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Advantages Of Blade PCs
Having the physical PCs in the datacenterreduces noise andheatat users' desks.
the pcs are inherently secure in a locked room.
Data cannot be downloadedor uploaded because the USB
ports and hard disk drives are away from the desk.
Incase of user/employer relocation the actual machinerelocation is avoided.
If a PC fails, a spare blade may be available in each chassis for
hot swapping. Repairs are always performed in the same place, andtechnicians do not have to travel throughout the building.
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A Blade PC
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ClearCube Technologies was the first to make blade PCs,which were introduced in 2000.
This ClearCube cage contains eight fully functional PCs,each with its own storage (hard disk).
A one-foot rack can hold nearly 20 PCs. So there is goodspace management.
ClearCube management software backs up the data tospare network drives, periodically.
if a blade fails, the mgmt software is used, to switch theuser to a spare blade and restore the data.
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A Blade Server
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Blade servers such as this unit from HP
are widely used in datacenters to save
space and ease systems management.
Managed by HP's Insight Manager, this
unit has redundant power supplies .
The exposed blade (left) is a complete
server with hard disk.
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Clustered Systems
A computer clusteris a group of tightly coupledcomputers which work together closely, so thatin many respects they can be viewed as thoughthey are a single computer.
The components of a cluster are in most casesconnected to each other through fast LANs andthey also share storage.
Clusters are usually deployed to improve
performance and availability Also typically they are much more cost-effectivethan single computers of comparable speed.
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High Availability is possible by adding a layer ofredundancy.
Imagine a layer of cluster software which runs onthe nodes.
Each node is made to monitor 1 or 2 othernodes.
If by chance a monitored machine fails, themonitoring machine can take ownership and can
restart the application. (the users cannot really notice this. There will
be a small interruption of service, thats all.)
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Types Of Clustering
There are different kinds of clusters
namely namely:-
(i) Asymmetric
(ii) Symmetric
(iii) Parallel clusters
(iv) WAN clusters
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Sep 2007 [email protected]
Assymetric Clustering
Means the machines are not alike in theirworking philosophy.
While one machine runs an application the
other is just a standby, also termed hotstandby.
The standby does nothing but monitors the
active server. And if the server fails the standby will take
over and will be the active server!
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Sep 2007 [email protected]
Symmetric Clustering
Here, 2 or more hosts are running
applications and are monitoring one
another.
If one fails the other will take over.
This is more efficient because the
machines act alike and resources on both
machines get used fully.
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Sep 2007 [email protected]
Parallel Clustering
Parallel clusters allow multiple hosts to
access the same data on the shared
storage. (cost effective & more reliable)
To provide multiple access simultaneously
the operating system too should provide
this facility and locking to ensure that no
conflicting operations occur.
This is termed distributed lock manager.
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However, since most operating systems
lack support forsimultaneous data
access by multiple hosts, special
versions of the software/applications arebeing used.
Eg:-Oracle parallel server is a version of
Oracles data base server designed to runon a parallel cluster.
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WAN Clusters
Custering over a wide area network
means the nodes are separated by high
distances. Eg:-a city area or so.
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SAN and clusters
Storage Area Networks allow many
systems to attach to a pool of storage.
If the applications and their data are
stored on the SAN, the cluster software
can assign the application to run on any
host.
If the host fails any other host can take
over.
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Grid computing
grid clusters are a technology closely related to clustercomputing.
The key differences (by definitions which distinguish thetwo at all) between grids and traditional clusters are that
grids connect collections of computers which do not fullytrust each other, or which are geographically dispersed.
Grids are thus more like a computing utility than like asingle computer.
In addition, grids typically support more heterogeneouscollections than are commonly supported in clusters.
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Grid computing is optimized for workloads which
consist of many independent jobs which do not
have to share data between the jobs during the
computation process. Grids serve to manage the allocation of jobs to
computers which will perform the work
independently of the rest of the grid cluster.
Resources such as storage may be shared by all
the nodes..
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An example of a very large cluster is thefolding@home project. It is analyzing data thatis used by researchers to find cures for diseasessuch as Alzheimer's and cancer.
Another large project is the seti@home project,which may be the largest distributed cluster inexistence. It uses approximately three millionhome computers all over the world to analyzedata from theArecibo Observatoryradiotelescope, searching for evidence ofextraterrestrial intelligence.
http://en.wikipedia.org/wiki/Arecibo_Observatoryhttp://en.wikipedia.org/wiki/Radiotelescopehttp://en.wikipedia.org/wiki/Radiotelescopehttp://en.wikipedia.org/wiki/Arecibo_Observatory -
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Computing Environments
Traditional computing
Client-server computing
Peer to peer computing Web based computing