CMD640
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 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
The original CMD640 has a data corruption bug. 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.
