TrueType was originally developed by Apple Computer in the late 1980s and has become the most common font format on both the Mac OS and Microsoft Windows operating systems. TrueType fonts can be scaled to any size and are clear and readable in all sizes. TrueType fonts are easier to install as it contain both the screen and printer font data in one file, but a different file is needed for each type-setting (e.g., normal, bold, italic, bold italic, etc).
What is OpenType Font?
OpenType format is a more recent format than TrueType, it is a joint effort from Adobe and Microsoft. Like TrueType, OpenType fonts contain both the screen and printer font data in a single file. OpenType fonts are cross-platform compatible making it easier to use same font file on both Mac OS or Windows operating systems, it has several exclusive capabilities like, it support greater extension of the basic character set, including old-style numerals, smallcaps, alternates, ligatures and more detailed shapes. OpenType fonts are also clear and readable in all sizes.