Having the CD on the same channel as the HD will not slow the HD down. Each device will run at available speeds. During transfers from CD direct to HD will be slower because they have to share the channel, but regular HD operation will be unaffected. I always say to put the devices that will be transferring a lot on different channels. If you will be burning from both the HD and the CD-ROM "on-the-fly" then put the CD-ROM and HD on the primary channel and but the burner as master on the secondary channel. If you won't ever be burning on the fly from CD-ROM, then put the CD-ROM as slave to the burner so that installations from CD-ROM to HD will be improved. If you have a second hard drive and will do a lot of HD to HD transfer, then make sure they are on separate channels and if you will be burning from the second hard drive primarily, then put the burner on the primary slave and put the second HD as secondary master with the CD-ROM as secondary slave. It really depends on how you want to do your read/writes.