Choosing an interface for an external CD-ROM drive (legacy PCs) Which controller standard natively supports connecting an external CD-ROM drive?

Introduction / Context:
Before USB became universal, external optical drives commonly used SCSI. Knowing which legacy interfaces supported external devices helps with maintaining older workstations and lab equipment.

Given Data / Assumptions:

• We consider classic PC storage interfaces: MFM, ESDI, and SCSI.
• Goal is to connect an external (out-of-chassis) CD-ROM unit.
• SCSI supports daisy-chaining and defined external cabling/terminations.

Concept / Approach:

MFM and ESDI are internal HDD interfaces with ribbon cables and no standardized external cabling for removable optical drives. SCSI, by design, supports multiple internal and external devices, using external connectors (e.g., Centronics, DB-25, HD-50, VHDCI) and termination rules. Many professional external CD-ROM and CD-R units shipped with SCSI.

Step-by-Step Solution:

Verification / Alternative check:

Vendor datasheets for classic external CD-ROMs cite SCSI IDs, termination switches, and external connectors—confirming SCSI as the intended interface.

Why Other Options Are Wrong:

MFM and ESDI target internal drives; ARLL is not a standard external optical interface. “None of the above” fails because SCSI is correct.

Common Pitfalls:

Confusing SCSI with parallel-port adapters (which were slower and used different protocols); forgetting to set SCSI IDs and termination on a chain.

Final Answer:

SCSI.