The Byte/Word eXtensions were first introduced in the EV56 and has been available in all subsequent models. The instructions were provided to reduce the number of instructions for operations such as loading and storing bytes or words to and from memory and sign-extending of byte and word values. According to the Alpha Architecture Handbook  it is recommended to use these instructions on platforms where they are present instead of the sequences of extract, mask and insert instructions that would otherwise be needed.
|LDBU||Load byte unaligned|
|LDWU||Load word unaligned|
To determine the presence of BWX, use the amask instruction.