A multiprocessor is a computer system with two or more central processing units (CPUs), with each one sharing the common main memory as well as the peripherals. This helps in simultaneous processing of programs. The key objective of using a multiprocessor is to boost the system’s execution speed, with other objectives being fault tolerance and application matching. A good illustration of a multiprocessor is a single central tower attached to two computer systems. A multiprocessor is regarded as a means to improve computing speeds, performance and cost-effectiveness, as well as to provide enhanced availability and reliability.

1. Multiprocessor Architecture
Asst. Prof. Vani Malagar

2. Contents
 Introduction to Multiprocessing Systems
 Types of Multiprocessing Systems
 Advantages of Multiprocessing
 Examples to Multiprocessors
 Interconnection Structures
Asst. Prof. Vani
Malagar

3. Introduction
 Multiprocessing is the use of two or more central processing units (CPUs) within a
single computer system. The term also refers to the ability of a system to support
more than one processor and/or the ability to allocate tasks between them.
 The term ‘processor’ in multiprocessor can mean either a CPU or an input-output
processor (IOP).
 There are some similarities between multiprocessor and multicomputer systems
since both support concurrent operations. However, there exists an important
distinction between the two.
 In case of multicomputer systems, several autonomous computers are connected
through a network that may or may not communicate with each other. On the
other hand, in a multiprocessor system, processors interact with each other
through an operating system and cooperate in the solution of a problem.
 Eg. Satellite Launching
Asst. Prof.
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4. Asst. Prof. Vani Malagar

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6. Asst. Prof. Vani Malagar

7. Advantages of Multiprocessing
 A benefit derived from multiprocessing is improved system performance. This
happens because computations can proceed in parallel in one of two ways:-
a) Multiple independent jobs can be made to operate in parallel.
b) A single job can be partitioned into multiple parallel tasks.
 Increased Reliability: A failure or error in one part has a limited effect on the rest
of the system. If a fault causes one processor to fail, a second processor can be
assigned to perform the functions of the disabled processor.
 Increased Throughput: An increase in the number of processors completes the
work in less time. It is important to note that doubling the number of processors
does not halve the time to complete a job.
Asst. Prof.
Vani

8. Classification
Multiprocessors are classified by the way their memory is organized. There
are two main kinds of multiprocessing systems:-
 Tightly Coupled Systems (Common Shared Memory)
 Loosely Coupled Systems (Distributed Memory)
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9. Tightly Coupled Systems
 A multiprocessor system with common shared memory is classified as a shared-
memory or tightly coupled multiprocessor.
 This does not prevent each processor from having its own local memory.
 In fact, most commercial tightly coupled multiprocessors provide a cache memory
with each CPU. In addition, there is a global common memory that all CPUs can
access. Information can be therefore be shared among the CPUs by placing it in
the common global memory.
 Symmetric multiprocessing (SMP) involves a multiprocessor system architecture
where two or more identical processors connect to a single, shared main memory,
have full access to all I/O devices, and are controlled by a single operating system
instance that treats all processors equally, reserving none for special purposes.
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Vani

10. Diagram
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11. Loosely Coupled Systems
 An alternative model of microprocessor is the distributed memory or loosely
coupled system.
 Each processor element in a loosely coupled system has its own private local
memory.
 The processors are tied together by a switching scheme designed to route
information from one processor to another through a message-passing scheme.
 Loosely coupled systems are most efficient when the interaction between tasks is
minimal unlike tightly coupled systems can tolerate a higher degree of interaction
between tasks.
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Vani

12. Beowulf Cluster
The Borg, a 52-node Beowulf
cluster, is an example of a
loosely-coupled system. It is a
high-performance
computing cluster
parallel
from
inexpensive personal computer
hardware.
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13. Tightly & Loosely
Coupled Microprocessors
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14. Low coupling
CPU’s located at different Locations
No sharing of Buses , I/O devices etc
Efficient when tasks running on different processors has minimal interaction
between them (parallel applications).
No memory conflict occurs.
Processors communicate with each other by using message –passing.
Data Rate is low (becoz of different Location)
larger in size .
Scalability is high.
More Fault tolerant
Complex due to additional hardware is req.
Less portable
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15. Complete the Characteristics using the Tightly Coupled Microprocessor
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16. Types of Systems using the different Memory
organization :
UMA – (Tightly Coupled) –[Symmetric & Asymmetric]
NUMA – (Tightly Coupled )
COMA – (Loosely Coupled )
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17. UMA & NUMA
 Uniform memory access (UMA) is a shared memory architecture used in parallel
computers. All the processors in the UMA model share the physical memory
uniformly. The UMA model is suitable for general purpose and time sharing
applications by multiple users.
 Non-uniform memory access (NUMA) is a computer memory design used in
multiprocessing, where the memory access time depends on the memory location
relative to the processor. Under NUMA, a processor can access its own local
memory faster than non-local memory (memory local to another processor or
memory shared between processors).
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19. UMA & NUMA
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20. Opteron
Opteron is AMD's x86 server and
workstation processor line, and was
the first processor which supported
the AMD64 instruction set
architecture (known generically as
x86-64).
The Opteron is a Non-Uniform
Memory Access (NUMA)
architecture.
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22. Structure of Multiprocessor
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23. Interconnection Structures
Some of the physical forms available for establishing an interconnection
network between the components of a multiprocessor system are:
The collection of paths that connects the various modules such as CPU, I/O
processors ,Memory etc in order to communicate with each other is called
Interconnection structures.
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Vani

24. Physical Forms Includes :
 Time-shared common bus
 Multiport memory
 Crossbar switch
 Multistage switching Network
 Hypercube System
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25. Interconnection Topologies
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26. Time-Shared Common Bus
Memory
Unit
CPU 1 CPU 2 CPU 3 IOP 1 IOP 2
The main limitation of shared-bus multiprocessors is that the common bus tends to be the
primary source for contention, and thus imposes a limit on the number of processors in the
system. Alternative architectural features are necessary to reduce the memory bandwidth
demands and to increase the bus bandwidth.
Overcome by Cache Asst. Prof.
Vani

27. How to Overcome bus –
oriented Interconnection
Use of cache associated with each Processor.
Use of hierarchy of buses :
Local Bus
System Bus
Expansion Bus
.
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29. Multiport Memory
MM 1 MM 2 MM 3 MM 4
CPU 1
CPU 2
CPU 3
CPU 4
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30. Cross Bar
Switch
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31. Crossbar Switch
MM 1 MM 2 MM 3 MM 4
CPU 1
CPU 2
CPU 3
CPU 4
Decrease
the cables
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35. Multistage Switching
•Applied to build large Multiprocessor systems like Omege, Butterfly etc
•The switching Network can connect any Input to any Output by making appropriate
communication to each.
CPU
Memory
End’s
Switching
elements
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38. Hypercube
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41. Formulae:
N=8 ,then each node has direct
log (8)=3 other nodes connected
to it.
Hypercube composed of N=2^n
processor connected in an n-
dimensional binary cube.
E.g. N=1 then N=2^1=2
Processors
N=2 then N=2^2=4
Processors
Asst. Prof.
Vani

42. References
 Computer System Architecture, 3rd Edition by M. Morris Mano, Pearson Education
 Computer Architecture-A Quantitative Approach, 4th Edition by Hennessy and
Patterson
 http://en.wikipedia.org/wiki/Multiprocessing
 http://en.wikipedia.org/wiki/Symmetric_multiprocessing

43. Thank You! 
12/09/14 Arpan Baishya 14MCA0015 Asst. Prof.
Vani