PC hardware: On a system that uses an Enhanced IDE (EIDE/ATA) controller, where is it best practice to connect an ATAPI/ATA CD-ROM drive so that the hard disk on the primary channel is not slowed by optical-drive PIO operations?

Introduction / Context:
Choosing the correct connector for an ATA/ATAPI CD-ROM drive in a desktop with an EIDE controller affects system performance and compatibility. Older optical drives often used lower transfer modes than hard drives, so cabling strategy matters.

Given Data / Assumptions:

• EIDE motherboard with two IDE channels: primary and secondary.
• Hard disk typically configured as Primary Master.
• Optical drive is an ATAPI device (CD-ROM).
• Goal is stable operation without degrading HDD throughput.

Concept / Approach:

Each IDE channel shares bandwidth between two devices. Mixing a slow PIO optical drive with a fast HDD on the same channel can force the controller to a slower timing during simultaneous access. Placing the optical drive on the different channel avoids this contention.

Step-by-Step Solution:

Verification / Alternative check:

Benchmarks show independent-channel transfers (HDD on primary, optical on secondary) prevent the optical's slow PIO/DMA mode from throttling the HDD. Optical drive access during disk operations does not stall HDD as severely when channels are separated.

Why Other Options Are Wrong:

• on the floppy bus: Floppy interface (FDD) uses a different 34-pin controller; optical drives are ATA/ATAPI, not FDD.
• on the primary IDE: Works, but can degrade HDD performance when shared; not best practice.
• on the SCSI bus: Only for SCSI optical drives; an ATA CD-ROM is not SCSI.
• All of the above: Interfaces are not interchangeable; only the correct IDE channel applies.

Common Pitfalls:

Incorrect master/slave jumper settings, mixing 40-wire and 80-wire cables, and enabling Cable Select without matching cables cause detection issues. Ensure BIOS set to Auto/ATAPI for the optical drive.

Final Answer:

on the secondary IDE