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CMD 640b PCI IDE controller

CMD640, the California Micro Devices 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 (a subsidiary[2] of Zeos) 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]