What Gets Sent: The Buffer
First generation message passing systems only allowed one to transmit information originating in a contiguous array of bytes
- Hid the real data structure from hardware and programmer
- Might make it hard to provide efficient implementations as implied a lot of expensive memory accesses
- Required pre-packing dispersed data, e.g.:
- Rows (in Fortran, columns in C) of a matrix must be transposed before transmission
- Prevented convenient communication between machines with different data representations