Although the message passing calls will work with any size or alignment of buffers, the hardware works only with well-aligned buffers. Therefore, the software must copy misaligned messages into aligned buffers before sending, thereby degrading performance.
On the iPSC/860, it is a good practice to ensure that the size of each buffer is a multiple of four bytes. For this, in C, buffers should be declared with int or long, rather than char or short. Buffers allocated with malloc or calloc will be correctly aligned.