Hornbein said:
It's actually the Roman alphabet, which is used to transliterate English. This is one reason spelling English is strange, with the a in tape and tap pronounced differently. Why wasn't a separate symbol used for the two distinct sounds? I doubt anyone knows. Many other languages are transliterated to Roman letters, but often accent marks are added.
The English alphabet is based on the Latin alphabet to be sure, but English has added letters which were not used at all by the Romans or were used only to write words from foreign (to the Romans) languages. (J, V, W, and Y in particular were added after Rome fell. K was rare (Kalends), as was Z, which was used for certain place names or for words borrowed from Greek)
Some language scripts (like French and Spanish) use diacritical marks or accents to indicate which syllable is stressed or how a vowel is to be sounded. Greek uses different letters sometimes to indicate a long vowel sound (omega, literally 'big o' v. omicron, lit. 'little o'), but in general, the Indo-European languages use different means to indicate the length of the vowel sound instead of adding letters. This keeps the number of letters to a minimum.
Some languages, like German, will use a double letter to indicate a lengthened vowel sound, like the word 'Meer' (sea). German also will add an 'h' after a vowel also to indicate the vowel is long, e.g. 'Sohn' (son).
In English, the rules are more complicated. The word 'tape' falls into a category where a single-syllable word ending in 'e' usually has a lengthened vowel preceding the 'e', so we have 'tape' v. 'tap' or 'nape' v. 'nap', 'hope' v. 'hop', 'gape' v. 'gap', and so on. This category has exceptions like 'pare', where the 'a' is short, but 'pane', where the 'a' is long.
One of the reasons why English orthography (how a language is written) is complicated and contradictory is that printing caused the written language to become standardized while great shifts in pronunciation were occurring or about to occur. For English, printing in the 16th century caused the language to be written in a certain way, but in the 17th century, a 'Great Shift' occurred in how some vowels were sounded, but this shift was not reflected in major changes in English spelling. In the great works of English literature written in the 16th century, like Shakespeare's plays and poetry, there are a number of rhymes and puns which were used and understood by his audiences which are no longer recognized by modern audiences because of this shift in English pronunciation.