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Why Hard Drive may not be identifiable by BIOS.

One of the major sign of a serious hard-drive failure is a simple and verifiable fact that a drive can no longer be detected by CMOS. Bad drive is dead for operating system because its inability to pass any BIOS POST checking commands.

Soundless hard drive – when connected to power supply wire - is the other reason to suspect a stuck motor of malfunctioning electronics as cause of failure. “Spins and clicks” scenario is the worst combination for data safety before it comes to specialist. You’d better stop it immediately.

Maybe the most tricky case when drive have normal sound of working drive, spins OK, no clicks, and still no detection in BIOS.A set of in-lab drive tests are needed to detect what’s wrong with such drive. One of probable cause might be a corrupt microcode on the platters (and partially – in drive’s ROM) which is as part of special internal program controlling all drive procedures, including seeking and reading data on sectors.

There is a known fact that improper electronic board testing (PCB) can be harmful for the later drive revival for data retrieving. Incompatible parts of microcode ( outside - on PCB, and inside – on disks) can confuse the drive’s software system and ruin essential pieces of digital code intrinsic to unique combination servo-formatting characteristics with mechanical properties of used reading/writing heads. Just keep in mind, some drives are full-tolerant to such experiments, other are not.

Primary Hard Disk Drive not found - a message from CMOS

Short Glossary for Disk detection in typical CMOS and LBA Translation Method

Example of drive detection in CMOS