TTF vs OTF
TTF and OTF are extensions that are used to indicate that the file is a font, which can be used in formatting the documents for printing. TTF stands for TrueType Font, a relatively older font, while OTF stands for OpenType Font, which was based in part on the TrueType standard.
A significant difference between the two is in their capabilities. TTF depends solely on glyph tables that define how each character looks while OTF is able to use glyphs along with CCF (Compact Font Format) tables. The cubic Bezier splines used by CCF allow for fewer points to be used in defining how a character would look compared to the quadratic Bezier splines used by TTF fonts. OTF also adds a few smartfont features, on top of the sfnt structure that is being used by TTF, to add additional language support to the fonts. Although it may not have a very significant effect on your computer, it is also worthy to note that the use of CCF in OTF could lead to file sizes that are significantly smaller, given that no special features are used in the font.
Despite the proven superiority of OTF fonts, especially when using CCF, the use of TTF fonts is still very prolific. It may be taking much longer than expected, but the number of OTF fonts is already on the rise. The reason behind this popularity is the simplicity of making TTF fonts compared to OTF fonts that use CCF. Since there is really no reason to stop using TTF in creating new fonts, most font makers still stick to what they know works, even if it is inferior to the alternative.
There is really no issue for the end user as almost all modern applications that uses fonts are able to work with TTF and OTF files. Users don’t needto choose one over the other as they can be used together in creating documents or printing layouts.
TrueType was invented by Apple as a competition to Adobe’s PostScript Type1. Both TrueType and PostScript fonts became the standard file formats for fonts for the past 3 decades or so of desktop publishing. In terms of your average designer, the differences between the two are relatively unimportant.
OpenType was designed to replace these and was created initially by Adobe and Microsoft. It’s basically a newer format that is more robust. For a designer, the primary benefits of OpenType over previous formats are a) an much larger character set and b) automatic alternative character and ligature support (for software that supports it).