By the beginning of the Viking Age, the Scandinavian rune-masters had developed an alphabet, or “futhark” (from the value of the first six characters), of sixteen characters that was quite distinct from the rest of the Germanic peoples. This alphabet was known as the “younger futhark”.
However, even within Scandinavia, there was no standard form for the characters and there are variations from inscription to inscription, but basically there were two main forms of futhark: the Common or Danish futhark (although it occurs outside of Denmark), and the Swedo-Norwegian futhark (although this also occurs outside of Sweden and Norway.
One can see that there are shortcomings with these alphabets. For example, there are characters for b, k and t, but there are none for p, g and d (this is because the futhark does not distinguish between these voiced and voiceless pairs. Therefore the rune-master had to use b for p, k for g and t for d.
There were other peculiarities: although there were two characters for the two different types of a, there were no symbols for e and o. This meant that the name “Svein” appears as in runes “suin” and the name “Gormr” appears as “kurmR”.
It becomes even more complicated, as the spelling practice allowed n to be omitted when it occurred before a consonant. Therefore the name Thormundr appears as thurmutR.
This of course means that many runic inscriptions can be very difficult to read and there can be a great deal of dispute about their true meaning.
Despite the difficulties in reading runic inscriptions, they can provide a good deal of useful information.
Source: Swedish National Museum Heritage Board’s website, but that page no longer exists.