6.4   Data conversion

PVM version 2

• PVM insures the needed conversions if the different hosts use different data representation (IEEE, IBM..., big/little endian...)
• PVM converts data using XDR
• If all the host have the same data representation, there will be no conversion (even if there is different types of host)
• Else
  • The majority representation is chosen as a ``standard''
  • The data will be send on this standard on the network
  • The hosts using a different representation realize local conversions
  • If two ``minority'' hosts communicate, there will be 2 conversions
• Alternatives
  1. The sender converts the data into the format of the receiver The sender has to know the format of each of the other hosts
  2. In order to avoid to code this information, all the data are converted into a format independent of the hosts and of the network The receiver converts the data from that format to its own format

PVM version 3

• The fact that the virtual machine is homogeneous may be corrupted by the dynamic adding of a new host in the virtual machine
• Depending on the user declaration
  • Either PVM 3 always uses XDR
  • Or no conversions are done