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CMD640, the CMD Technology Inc product 0640, is an IDE interface chip for the PCI and VLB buses. CMD640 had some sort of hardware acceleration: WDMA and Read-Ahead (prefetch) support.

CMD Technology Inc was acquired by Silicon Image Inc. in 2001.

Chip Protocol
SiI/CMD 640 MDMA 1
SiI/CMD 643 MDMA 2
SiI/CMD 646 UDMA 2
SiI/CMD 648 UDMA 4
SiI/CMD 649 UDMA 5
SiI0680 UDMA 6

Hardware bug[edit]

The original CMD640 has a data corruption bug.[1] The data corruption bug is similar to the bug affecting the contemporaneous PC Tech RZ1000 chipset. Both chipsets were used on a number of motherboards, including those from Intel.

Мodern operating systems have a workaround for this bug by prohibiting aggressive acceleration mode and losing about 10% of the performance.


External links[edit]