Convert DVD-10 (DoubleSide/SingleLayer) to byte

A CD holds 650 MB of data (74 minutes of audio) or 700 MB (80 minutes). DVDs and Blu-ray discs are sold by nominal capacity: 4.7 GB for a single-layer DVD-5, 8.5 GB for the dual-layer DVD-9, double that for the double-sided DVD-10 and DVD-18, and 25 GB per layer for Blu-ray, so 50 GB for a dual-layer disc. As with hard drives, packaging counts in decimal gigabytes while operating systems display binary ones, so a disc always looks smaller on screen than on the box.

A bit is a single 0 or 1, and a byte is eight of them, 256 possible values, enough for one Latin letter: a byte has been 8 bits since the IBM System/360 of 1964, and 'octet' says so explicitly, which is why French writes Mo rather than MB. Bits are counted where single ones matter – 16-bit audio, 24-bit colour, 256-bit keys, internet speeds – and bytes where data is stored: an emoji takes 4 bytes in UTF-8, a photo a few million, a film a few billion. Lower-case b is bits, capital B bytes.