Editing DEC Alpha (section)

===Motion Video Instructions (MVI)===
Motion Video Instructions (MVI) was an instruction set extension to the Alpha ISA that added instructions for [[single instruction, multiple data]] (SIMD) operations.<ref>Gwennap, Linley (18 November 1996). "Digital, MIPS Add Multimedia Extensions". ''[[Microprocessor Report]]''.</ref> Alpha implementations that implement MVI, in chronological order, are the [[Alpha 21164#Alpha 21164PC|Alpha 21164PC]] (PCA56 and PCA57), [[Alpha 21264]] (EV6) and [[Alpha 21364]] (EV7). Unlike most other SIMD instruction sets of the same period, such as [[MIPS architecture|MIPS]]' [[MDMX]] or [[SPARC]]'s [[Visual Instruction Set]], but like [[PA-RISC]]'s [[Multimedia Acceleration eXtensions]] (MAX-1, MAX-2), MVI was a simple instruction set composed of a few instructions that operate on integer data types stored in existing integer registers.

MVI's simplicity is due to two reasons. Firstly, Digital had determined that the [[Alpha 21164]] was already capable of performing [[DVD]] decoding through software, therefore not requiring hardware provisions for the purpose, but was inefficient in [[MPEG-2]] encoding. The second reason is the requirement to retain the fast cycle times of implementations. Adding many instructions would have complicated and enlarged the instruction decode logic, reducing an implementation's clock frequency.

MVI consists of 13 instructions:

{| class="wikitable"
|-
! width="120" | Mnemonic
! width="360" | Instruction
|-
| <code>MAXSB8</code>
| Vector Signed Byte Maximum
|-
| <code>MAXSW4</code>
| Vector Signed Word Maximum
|-
| <code>MAXUB8</code>
| Vector Unsigned Byte Maximum
|-
| <code>MAXUW4</code>
| Vector Unsigned Word Maximum
|-
| <code>MINSB8</code>
| Vector Signed Byte Minimum
|-
| <code>MINSW4</code>
| Vector Signed Word Minimum
|-
| <code>MINUB8</code>
| Vector Unsigned Byte Minimum
|-
| <code>MINUW4</code>
| Vector Unsigned Word Minimum
|-
| <code>PERR</code>
| Pixel Error
|-
| <code>PKLB</code>
| Pack Longwords to Bytes
|-
| <code>PKWB</code>
| Pack Words to Bytes
|-
| <code>UNPKBL</code>
| Unpack Bytes to Longwords
|-
| <code>UNPKBW</code>
| Unpack Bytes to Words
|-
|}

{{Multimedia extensions}}