DOS boot sequence — system files checked at startup: Each time you power on a DOS PC, which core system files are loaded/checked during the bootstrap process?

Introduction / Context:
Legacy DOS boot relies on a small set of critical system files. Technicians often need to know the minimum files for a bootable disk, especially when repairing corrupted systems or creating startup media.

Given Data / Assumptions:

• DOS expects specific hidden system files in the root of the boot drive.
• File names vary slightly by DOS version, but the trio IO.SYS, MSDOS.SYS, and COMMAND.COM is canonical in MS-DOS.
• The question asks which files are checked/loaded at power-on.

Concept / Approach:

The BIOS loads the boot sector, which then loads the DOS system files. IO.SYS initializes hardware interfaces, MSDOS.SYS provides the DOS kernel services, and COMMAND.COM is the command interpreter. If any are missing or corrupted, boot typically fails or drops to a minimal shell.

Step-by-Step Solution:

Verification / Alternative check:

Creating a bootable floppy with SYS A: places IO.SYS, MSDOS.SYS, and COMMAND.COM in the root, proving these three are required at startup.

Why Other Options Are Wrong:

• COMMAND.COM, IO.SYS: Incomplete; missing MSDOS.SYS (the kernel).
• COMMAND.COM, DATE.COM, TIME.COM: DATE/TIME are utilities, not core boot files.
• CHKDSK.EXE: Diagnostic tool; not a boot prerequisite.
• None of the above: Incorrect because the correct trio is provided.

Common Pitfalls:

Assuming CONFIG.SYS or AUTOEXEC.BAT are required for boot; they are processed after the core files load. Also, mixing PC-DOS names and MS-DOS names across versions.

Final Answer:

COMMAND.COM, IO.SYS, MSDOS.SYS