Setup guide

OSx Migration Cookbook August 30, 2006

2 – Comparing OSx and PCS 7

Client/Server vs.

Peer-to-Peer

Before proceeding with a migration project, understanding the

differences and similarities between OSx and PCS 7 is crucial.

Two architectures have been used for OSx and PCS 7: client/server

and peer-to-peer.

In a client/server architecture the HMI (Human Machine Interface –

the user interface) resides on a computer known as a client, and the

reference copy of the data resides on a computer known as a server.

The server provides the data to the client on request. Client

computers do not communicate with PLCs and do not directly

interact with the process. They do so via their host server. Tistar

and PCS 7 are examples of client/server systems.

Because the loss of a server is significant, Tistar and PCS 7 both

allow the use of redundant pairs of servers. Tistar only supports one

pair of redundant servers, and only on the Tistar model 70 version

2.0.0. Most Tistar models do not support redundancy.

PCS 7 supports a distributed client/server architecture. Up to twelve

redundant server pairs are supported. Each pair could have access to

part of the process, and each client can access any of the pairs to

view any part of the whole process. By distributing the process

among the servers, the impact of failure is minimized and the

processing load is spread out among several computers.

OSx is an examples of a distributed peer-to-peer system. In a peer-

to-peer system, all computers can directly interact with the PLCs

and the process. Two types of peer-to-peer systems exist:

distributed and non-distributed. In a distributed system some

stations have specialized functions, such as gathering trend data or

creating reports. As a result, not all data may be on all stations.

Functions and data are distributed. In a non-distributed system, all

data and all functions are on all stations.

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