My hard drive has a size of xxGB. Why is my hard disk size wrongly reported as yyGB?

Recommended by Wim's BIOS...

Drive makers "define" their gigabyte as a billion of bytes, 10^9 or 1,000,000,000. Megabytes are 10^6 or 1,000,000 bytes here.

Real binary gigabytes are 2^30 bytes or 1,073,741,824 bytes. Megabytes are 2^20 or 1,048,576 bytes.

To make things worse, software can display either version. FDISK displays binary megabytes 2^20, so does the HPT's BIOS. Your system BIOS seems to sell 10^6 bytes for a HDD megabyte.

Doing the math, you'll see that's where your MB have "vanished", exactly the difference between decimal and "real" binary megabytes, rounding errors aside.

Windows 98's Drive Properties window displays capacity in bytes, plus decimal and binary megabytes, so have a look there to have it all side by side.

PS: Blame points to Quantum. They started doing that with the LP105 series. Even back then, people called in and complained "where are my five megabytes" since each and every software back then displayed capacity as 100.3 (binary) megabytes.

Quantum's drive specification sheet then was added a footnote (in 1pt Flyspeck Sans Serif font, of course) that said "Quantum defines 1 Megabyte as 1,000,000 bytes" ...

Go back to our BIOS FAQ.

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