3DNow!

Template:Short descriptionTemplate:Infobox computer hardware 3DNow! is a deprecated extension to the x86 instruction set developed by Advanced Micro Devices (AMD). It adds single instruction multiple data (SIMD) instructions to the base x86 instruction set, enabling it to perform vector processing of floating-point vector operations using vector registers. This improvement enhances the performance of many graphics-intensive applications. The first microprocessor to implement 3DNow! was the AMD K6-2, introduced in 1998. In appropriate applications, this enhancement raised the speed by about 2–4 times.<ref>Template:Cite web</ref>

However, the instruction set never gained much popularity, and AMD announced in August 2010 that support for 3DNow! would be dropped in future AMD processors, except for two instructions, PREFETCH and PREFETCHW.<ref>Template:Cite web</ref> These two instructions are also available in Bay-Trail Intel processors.<ref>Template:Cite web</ref>

History

3DNow! was developed at a time when 3D graphics were becoming mainstream in PC multimedia and games. Realtime display of 3D graphics depended heavily on the host CPU's floating-point unit (FPU) to perform floating-point calculations, a task in which AMD's K6 processor was easily outperformed by its competitor, the Intel Pentium II.

As an enhancement to the MMX instruction set, the 3DNow! instruction-set augmented the MMX SIMD registers to support common arithmetic operations (add/subtract/multiply) on single-precision (32-bit) floating-point data. Software written to use AMD's 3DNow! instead of the slower x87 FPU could execute up to four times faster, depending on the instruction mix.

Versions

3DNow!

The first implementation of 3DNow! technology contains 21 new instructions that support SIMD floating-point operations. The 3DNow! data format is packed, single-precision, floating-point. The 3DNow! instruction set also includes operations for SIMD integer operations, data prefetch, and faster MMX-to-floating-point switching. Later, Intel would add similar (but incompatible) instructions to the Pentium III, known as SSE (Streaming SIMD Extensions).

3DNow! floating-point instructions are the following: Template:Div col

• PI2FDTemplate:Snd Packed 32-bit integer to floating-point conversion
• PF2IDTemplate:Snd Packed floating-point to 32-bit integer conversion
• PFCMPGETemplate:Snd Packed floating-point comparison, greater or equal
• PFCMPGTTemplate:Snd Packed floating-point comparison, greater
• PFCMPEQTemplate:Snd Packed floating-point comparison, equal
• PFACCTemplate:Snd Packed floating-point accumulate
• PFADDTemplate:Snd Packed floating-point addition
• PFSUBTemplate:Snd Packed floating-point subtraction
• PFSUBRTemplate:Snd Packed floating-point reverse subtraction
• PFMINTemplate:Snd Packed floating-point minimum
• PFMAXTemplate:Snd Packed floating-point maximum
• PFMULTemplate:Snd Packed floating-point multiplication
• PFRCPTemplate:Snd Packed floating-point reciprocal approximation
• PFRSQRTTemplate:Snd Packed floating-point reciprocal square root approximation
• PFRCPIT1Template:Snd Packed floating-point reciprocal, first iteration step
• PFRSQIT1Template:Snd Packed floating-point reciprocal square root, first iteration step
• PFRCPIT2Template:Snd Packed floating-point reciprocal/reciprocal square root, second iteration step

3DNow! integer instructions are the following:

• PAVGUSBTemplate:Snd Packed 8-bit unsigned integer averaging
• PMULHRWTemplate:Snd Packed 16-bit integer multiply with rounding

3DNow! performance-enhancement instructions are the following:

• FEMMSTemplate:Snd Faster entry/exit of the MMX or floating-point state
• PREFETCH/PREFETCHWTemplate:Snd Prefetch at least a 32-byte line into L1 data cache (this is the only non-deprecated instruction)

3DNow! extensions

There is little or no evidence that the second version of 3DNow! was ever officially given its own trade name. This has led to some confusion in documentation that refers to this new instruction set. The most common terms are Extended 3DNow!, Enhanced 3DNow! and 3DNow!+. The phrase "Enhanced 3DNow!" can be found in a few locations on the AMD website but the capitalization of "Enhanced" appears to be either purely grammatical or used for emphasis on processors that may or may not have these extensions (the most notable of which references a benchmark page for the K6-III-P that does not have these extensions).<ref name="extman">Template:Cite web</ref><ref>Template:Cite web</ref>

This extension to the 3DNow! instruction set was introduced with the first-generation Athlon processors. The Athlon added five new 3DNow! instructions and 19 new MMX instructions. Later, the K6-2+ and K6-III+ (both targeted at the mobile market) included the five new 3DNow! instructions, leaving out the 19 new MMX instructions. The new 3DNow! instructions were added to boost DSP. The new MMX instructions were added to boost streaming media.

The 19 new MMX instructions are a subset of Intel's SSE instruction set. In AMD technical manuals, AMD segregates these instructions apart from the 3DNow! extensions.<ref name="extman"/> In AMD customer product literature, however, this segregation is less clear where the benefits of all 24 new instructions are credited to enhanced 3DNow! technology.<ref>Template:Cite web</ref> This has led programmers to come up with their own name for the 19 new MMX instructions. The most common appears to be Integer SSE (ISSE).<ref>Template:Cite web</ref> SSEMMX and MMX2 are also found in video filter documentation from the public domain sector. ISSE could also refer to Internet SSE, an early name for SSE.

3DNow! extension DSP instructions are the following:

• PF2IWTemplate:Snd Packed floating-point to integer word conversion with sign extend
• PI2FWTemplate:Snd Packed integer word to floating-point conversion
• PFNACCTemplate:Snd Packed floating-point negative accumulate
• PFPNACCTemplate:Snd Packed floating-point mixed positive-negative accumulate
• PSWAPDTemplate:Snd Packed swap doubleword

MMX extension instructions (Integer SSE) are the following: Template:Div col

• MASKMOVQTemplate:Snd Streaming (cache bypass) store using byte mask
• MOVNTQTemplate:Snd Streaming (cache bypass) store
• PAVGBTemplate:Snd Packed average of unsigned byte
• PAVGWTemplate:Snd Packed average of unsigned word
• PMAXSWTemplate:Snd Packed maximum signed word
• PMAXUBTemplate:Snd Packed maximum unsigned byte
• PMINSWTemplate:Snd Packed minimum signed word
• PMINUBTemplate:Snd Packed minimum unsigned byte
• PMULHUWTemplate:Snd Packed multiply high unsigned word
• PSADBWTemplate:Snd Packed sum of absolute byte differences
• PSHUFWTemplate:Snd Packed shuffle word
• PEXTRWTemplate:Snd Extract word into integer register
• PINSRWTemplate:Snd Insert word from integer register
• PMOVMSKBTemplate:Snd Move byte mask to integer register
• PREFETCHNTATemplate:Snd Prefetch using the NTA reference
• PREFETCHT0Template:Snd Prefetch using the T0 reference
• PREFETCHT1Template:Snd Prefetch using the T1 reference
• PREFETCHT2Template:Snd Prefetch using the T2 reference
• SFENCETemplate:Snd Store fence

3DNow! Professional

3DNow! Professional is a trade name used to indicate processors that combine 3DNow! technology with a complete SSE instructions set (such as SSE, SSE2 or SSE3).<ref>Template:Cite web</ref> The Athlon XP was the first processor to carry the 3DNow! Professional trade name, and was the first product in the Athlon family to support the complete SSE instruction set (for the total of: 21 original 3DNow! instructions; five 3DNow! extension DSP instructions; 19 MMX extension instructions; and 52 additional SSE instructions for complete SSE compatibility).<ref>Template:Cite web</ref>

3DNow! and the Geode GX/LX

The Geode GX and Geode LX added two new 3DNow! instructions which is absent in all other processors.

3DNow! "professional" instructions unique to the Geode GX/LX are the following:

• PFRSQRTVTemplate:Snd Reciprocal square root approximation for a pair of 32-bit floats
• PFRCPVTemplate:Snd Reciprocal approximation for a pair of 32-bit floats

Advantages and disadvantages

One advantage of 3DNow! is that it is possible to add or multiply the two numbers that are stored in the same register. With SSE, each number can only be combined with a number in the same position in another register. This capability, known as horizontal in Intel terminology, was the major addition to the SSE3 instruction set.

A disadvantage with 3DNow! is that 3DNow! instructions and MMX instructions share the same register-file, whereas SSE adds 8 new independent registers (XMM0–XMM7).

Because MMX/3DNow! registers are shared by the standard x87 FPU, 3DNow! instructions and x87 instructions cannot be executed simultaneously. However, because it is aliased to the x87 FPU, the 3DNow! and MMX register states can be saved and restored by the traditional x87 F(N)SAVE and F(N)RSTOR instructions. This arrangement allowed operating systems to support 3DNow! with no explicit modifications, whereas SSE registers required explicit operating system support to properly save and restore the new XMM registers (via the added FXSAVE and FXRSTOR instructions.)

The FX* instructions from SSE provide a functional superset of the older x87 save and restore instructions. They can save not only SSE register states but also the x87 register states (hence are applicable also for MMX and 3DNow! operations where supported).

On AMD Athlon XP and K8-based cores (i.e. Athlon 64), assembly programmers have noted that it is possible to combine 3DNow! and SSE instructions to reduce register pressure, but in practice it is difficult to improve performance due to the instructions executing on shared functional units.<ref>Template:Cite newsgroup</ref>

Processors supporting 3DNow!

• All AMD processors after K6-2 (based on K6), Athlon, Athlon 64 and Phenom architecture families.
  • Not supported in Bulldozer, Bobcat and Zen architecture processors and their derivates.
  • The last AMD APU processor supporting 3DNow! is the A8-3870K, which is based on the Llano architecture. It is also the only APU with 3DNow! instructions, as the Bobcat and up exclude support for it.
• National Semiconductor Geode GX2, later AMD Geode.
• VIA C3 (also known as Cyrix III) "Samuel", "Samuel 2", "Ezra", and "Eden ESP" cores.
• IDT WinChip 2, 3

Further reading

• Case, Brian (1 June 1998). "3DNow Boosts Non-Intel 3D Performance". Microprocessor Report.
• Oberman, S.; Favor, G.; Weber, F. (March 1999). "AMD 3DNow technology: architecture and implementations". IEEE Micro.

External links

• 3DNow Technology Partners, archived from the original (removed from AMD's website in early 2001)
• AMD 3DNow Instruction Porting Guide (PDF), archived from the original (removed from AMD's website in 2014)
• 3DNow Technology Manual
• AMD Extensions to the 3DNow and MMX Instruction Sets Manual
• AMD Geode LX Processors Data Book
• AMD 3DNow! SDK March 1999, archived