Basic Block Size

Choosing the XDR block size requires a trade off. Choosing a small size such as two makes the encoded data small, but causes alignment problems for machines that are not aligned on these boundaries. A large size such as eight means the data will be aligned on virtually every machine, but causes the encoded data to grow too large. Four was chosen as a compromise. Four is big enough to support most architectures efficiently.

This is not to say that the computers cannot utilize standard XDR, just that they do so at a greater overhead per data item than 4-byte (32-bit) architectures. Four is also small enough to keep the encoded data restricted to a reasonable size.

The same data should encode into an equivalent result on all machines, so that encoded data can be compared or checksummed. So, variable length data must be padded with trailing zeros.