Why windows still boots from c: and leaves a: and b: as ghosts

Every Windows user sees it daily, yet almost no one asks why the main drive is stubbornly labeled C:. The answer is buried in 1970s magnetic disks that clicked like typewriters and stored less than a selfie.

The floppy ghosts that still own the first two letters

CP/M, the operating system that fathered DOS, hard-wired A: and B: for 5¼-inch floppies. When IBM cloned that scheme for its 1981 PC, the twin drives were expected to stay. Hard disks were an afterthought—expensive, refrigerator-noisy add-ons. IBM’s PC XT in 1983 squeezed a 10 MB Seagate into the same chassis and simply grabbed the next free letter. The choice was never aesthetic; it was the path of least resistance.

Microsoft inherited the convention with DOS 2.0 and, four decades later, still ships Windows 11 with the same alphabet. Redmond could have reclaimed A: once floppies vanished, but the company discovered something engineers have always known: legacy is the heaviest code. Swap the letter and every installer, registry key, and corporate script that hard-codes C: becomes a time bomb.

Enterprise inertia keeps the letter untouchable

Manufacturing lines, hospital imaging rigs and airport check-in kiosks still boot DOS-based firmware that expects C:. Microsoft internal data once showed that 0.7 % of active Windows devices in 2022 had at least one legacy 16-bit component in the boot chain. That sounds trivial—until you realize it represents millions of machines whose downtime is measured in dollars per second.

Meanwhile, the supposedly “free” letters A: and B: are still reserved at the kernel level. Try to rename an external SSD to either one and Disk Management will flash a warning most users have never seen. The OS quietly keeps the seats empty for hardware that will never again spin.

So the C: on your NVMe drive is not a letter; it is a fossilized footprint from an era when 360 KB was ample and 10 MB felt infinite. Microsoft isn’t clinging to nostalgia—it is handcuffed to its own install base. The alphabet ends at Z, but Windows starts at C, forever skipping the first two beats of the song it was taught in 1981.