In the 17th century the guitar was "cultivated by players and composers within the courts of princes and kings." The Baroque guitar was very much like the modern six string that we know today,
Aside from a difference of tuning the modern guitar is a baritone/tenor... the baroque is an alto instrument, about the size of a viola.
The differences in size and pitch change the sustain and articulation. The Baroque guitar's tonal characteristics are much more delicate, percussive, and lute-like. The greatest music for baroque guitar is difficult to render adequately on the modern guitar because the traditions of the two instruments have diverged so widely:
They speak basically the same language, but with a different vocabulary and accent. Early Renaissance guitars had what is called a "four course" string arrangement, with eight doubled strings. The baroque guitar added one more for a "five course" instrument with nine strings.
Like its Renaissance forebear, lutes, and modern twelve-string guitars today, four of those "courses" were doubled, with pairs of strings tuned to the same note. This essentially made it a five string guitar with the ringing sonority of a mandolin. The tuning was fairly close to a modern six-string, but one octave up and missing the low E. The lone high E string was called the chanterelle or "singing string."