We've all heard the claims made for archival-quality media, but M-Disc is a genuine and fundamental change in the way that discs are designed.
Unlike other disc media, the recordable data layer uses an inorganic glass-like material that has a much higher resistance to oxidation and high melting point (between 200 and 1000 degrees celcius). The DVD versions of M-Disc also do not require a reflective layer; this is the single largest cause of failure in most other recordable DVD media. Amonst other reasons, these are why M-Disc blank media has a predicted archival lifespan of 1000 years, beating its nearest competitor by around ten times.
IMPORTANT NOTE: M-Disc media can be played back or read in virtually any DVD drive. However, it needs an M-Disc compatible writer to be able to actually record. Please make sure that the burner/writer you're intending to record to this disc with is M-Disc compatible before ordering.
Number of items contained within a single pack.
The speed at which disc media (CD, DVD and BD-R) can be written. Note that the speeds for different media types are not the same (e.g. a 52x CD can not be written to around 3 times faster than a 16x DVD).