Currently, there are two kinds of IDE cables, one is 40 pins, and the other is 80 pins. Only 80 pins cable supports Ultra DMA mode. If you are using 40 Pins cable, the IDE device(HDD or CDROM) will be set into PIO mode. In this mode, CPU issued access commands, then fail into a loop to poll IDE device whether the data were transfer completly. You will see that CPU work in 100% during access IDE device.
For Ultra DMA mode, CPU issued a command, then IDE controller will transfer the data to/from memory. After access complete, it will generate a notice to CPU. Less than 50% will show in CPU usage.
For HDD, the data transfer rate is near 30 MB/S - Ultra DMA 3, 50MB/S - Ultra DMA 4, 80MB/S - Ultra DMA5. But less than 10MB/S - PIO.

If your CDROM writer support Ultra DMA mode, you should use 80 pins cable(ATA66=ATA100=ATA133 80Pins)
If your CDROM write doesn't support Ultra DMA mode, you still can use 80 Pins cable, but the preformance are the same.