Introduction to Multiprocessors - Fundamentals of Computer Organization and Architecture

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are (1) low communication overhead among processors while executing a given task

and (2) a degree of inherent parallelism in the task.

A number of communication styles exist for multiple processor networks. These

can be broadly classified according to (1) the communication model (CM) or (2) the

physical connection (PC). According to the CM, networks can be further classified

as (1) multiple processors (single address space or shared memory computation) or

(2) multiple computers (multiple address space or message passing computation).

According to PC, networks can be further classified as (1) bus-based or (2) network-

basedmultiple processors. Typical sizes of such systems are summarized in Table 11.1.

The organization and performance of a multiple processor system are greatly influ-

enced by the interconnection network used to connect them. On the one hand, a single

shared bus can be used as the interconnection network for multiple processors. On the

other hand, a crossbar switch can be used as the interconnection network. While the

first technique represents a simple easy-to-expand topology, it is, however, limited

in performance since it does not allow more than one processor

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memory transfer at

any given time. The crossbar provides full processor

memory distinct connections

but it is expensive. Multistage interconnection networks (MINs) strike a balance

between the limitation of the single, shared bus system and the expense of a

crossbar-based system. In a MIN more than one processor

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memory connection can

be established at the same time. The cost of a MIN can be considerably less than

that of a crossbar, particularly for a large number of processors and

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or memories.

The use of multiple buses to connect multiple processors to multiple memory modules

has also been suggested as a compromise between the limited single bus and the

expensive crossbar. Figure 11.1 illustrates the four types of interconnection networks

mentioned above. Interested readers are referred to our topic on Advanced Computer

Architecture and Parallel Processing (see reference list).

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11.2. CLASSIFICATION OF COMPUTER ARCHITECTURES

A classification means to order a number of objects into categories, each having

common features, among which certain relationship(s) exist(s). In this regard, a

classification scheme for computer architectures aims at categorizing them such

that those architectures that have common features fall into one category and

such that different categories represent distinct groups of architectures. In addition,

TABLE 11.1 Typical Sizes of Some Multiprocessor Systems

Number of

processors