I have harddisk and dvd-rom in the same cable.

[alqaedaarmy]

Both is on the same IDE cable. Will my harddisk perform slower? How much slower? For performance of games, ofcouse.

My harddisk is seagate 80gig 7200rpm.
Dvd-writer: lite-on

I heard that ATA133 will go down to the speed of ATA 33, is that correct? So it's about 4 times slower!!

Thanks!

[GrnEyedDvl]

Yes it will perform worse, IDE is limited to the speed of the slowest device on the channel.

[alqaedaarmy]

Could you specify in percentage? How much slower.

I benchmark with Sisof Sandra , it reports my harddisk is running normally on both circumstances as I took the DVD-rom out.

[shadowarmy75]

From wiki it says:

It is a common misconception that, if two devices of different speed capabilities are on the same cable, both devices' data transfers will be constrained to the speed of the slower device.

For all modern ATA host adapters (since the PIIX4 south bridge was introduced in 1997) this is not true, as modern ATA host adapters support independent device timing. This allows each device on the cable to transfer data at its own best speed.

Even with older adapters without independent timing, this effect only impacts the data transfer phase of a read or write operation. This is usually the shortest part of a complete read or write operation (except for burst mode transfers).

However, if you read further:

This is a much more important effect. It is caused by the omission of both overlapped and queued feature sets from most parallel ATA products. This means that only one device on a cable can perform a read or write operation at one time. Therefore, a fast device on the same cable as a slow device under heavy use will find that nearly every time it is asked to perform a transfer, it has to wait for the slow device to finish its own ponderous transfer.

For example, consider an optical device such as a DVD-ROM, and a hard drive on the same parallel ATA cable. With average seek and rotation speeds for such devices, a read operation to the DVD-ROM will take an average of around 100 milliseconds, while a typical fast parallel ATA hard drive can complete a read or write in less than 10 milliseconds. This means that the hard drive, if unencumbered, could perform more than 100 operations per second (and far more than that if only short head movements are involved). But since the devices are on the same cable, once a "read" command is given to the DVD-ROM, the hard drive will be inaccessible (and idle) for as long as it takes the DVD-ROM to complete its read—seek time included. Frequent accesses to the DVD-ROM will therefore vastly reduce the maximum throughput available from the hard drive. If the DVD-ROM is kept busy with average-duration requests, and if the host operating system driver sends commands to the two drives in a strict "round robin" fashion, then the hard drive will be limited to about 10 operations per second while the DVD-ROM is in use, even though the burst data transfers to and from the hard drive still happen at the hard drive's usual speed.

[alqaedaarmy]

That's so kind of you, thanks.
So the paragraph can be summarized by:

The speed of harddisk will be running at its fastest state, if dvd-rom drive is not busy. If dvd-rom is busy, the harddisk will be waiting for dvd-rom to finish first, which will be about 10 times slower than normal state.

imo