It is common to use numerals to refer to years, decades, and centuries. Decades and centuries are sometimes spelled out (for instance, “in the nineteenth century”), although numerals are also common (“in the 19th century”).
The earliest finds with runic inscriptions are dated to the 2nd century AD.
Philologists specialized in runes use a slightly broader spectrum for the Viking Age period, defining it as the era between 800–1100 AD.
The letter ‘s’ that comes after a year range indicates the plural of the years, not the possessive, and therefore no punctuation should be used between the numerals and the ‘s’.
Computers in the 1970s and early 1980s used cassette tapes for storage.