1. A method for executing a load-partial instruction, comprising: receiving the load-partial instruction to be executed, wherein the load-partial instruction specifies a source address in memory, which is possibly an unaligned address; and executing the load-partial instruction, which involves loading a partial-vector-sized datum from a naturally-aligned memory region encompassing the source address, and in doing so rotating the bytes of the partial-vector-sized datum to cause the byte at the specified source address to reside at the least-significant byte position within the partial-vector-sized datum for a little-endian memory transaction, or to cause the byte to be positioned at the most-significant byte position within the partial-vector-sized datum for a big-endian memory transaction.