GPU Wiki Architecture

TeraScale 3

TeraScale 3 (internally designated VLIW4) is the final evolution of AMD's VLIW shader family, used exclusively in the Radeon HD 6900 series (Cayman) launched in late 2010. By reducing the VLIW cluster width from 5 to 4 shader processors, AMD improved instruction packing efficiency — a direct response to compiler difficulty squeezing full utilization out of VLIW5 workloads.

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Launch era
2010 to 2012
Process nodes
40nm (TSMC)
Predecessor
TeraScale 2 (VLIW5)
Successor
GCN 1.0
Source review
Verified

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Architecture History

The HD 6970 and HD 6950 were competitive with NVIDIA's GeForce GTX 580 and represented AMD's last VLIW-based high-end desktop GPU before GCN.

More architecture facts

Architecture name
TeraScale 3 (VLIW4)
Important chips
Cayman XT (HD 6970), Cayman Pro (HD 6950)
Memory technologies
GDDR5 (256-bit)
Architecture feature generation
VLIW4 Stream Processors; DirectX 11 (FL 11_0); OpenCL 1.1
Consumer series
Radeon HD 6970, HD 6950
Workstation / professional series
ATI FirePro V9800 (Cayman)
Data center series
(None; compute focus shifted to GCN development)

What this architecture changed

VLIW4 cluster design: each shader processor group handles 4-wide VLIW instructions rather than VLIW5, improving compiler utilization and die efficiency.
Increase in shader processor count (1536 on Cayman XT) relative to Cypress (1600) with a smaller die by switching to VLIW4.
DirectX 11 feature level 11_0.
Side port memory removed compared to some earlier designs; unified GDDR5 bus.

Why it mattered

TeraScale 3 / VLIW4 represents AMD acknowledging the compiler limitations of wide VLIW designs. The move to 4-wide clusters was a stepping stone: it improved utilization without the full redesign that GCN would require. Cayman is historically significant as the last VLIW-architecture high-end AMD GPU, marking the end of a shader design philosophy that traced back to the ATI R300 generation. It is relatively uncommon in collector markets compared to the larger Evergreen lineup.