Before Unicode was widely accepted and supported, this meant representing the curved quotes in whatever 8-bit encoding the software and underlying operating system was using. The character sets for Windows and Macintosh used two different pairs of values for curved quotes, while ISO 8859-1 (historically the default character set for the Unixes and older Linux systems) has no curved quotes, making cross-platform and -application compatibility difficult.
Before Unicode became widely accepted and implemented, representing curved quotes was a challenge because software and operating systems used different encoding schemes. Windows and Macintosh had distinct sets of values for curved quotes, while ISO 8859-1 (the default character set for Unix systems and older Linux) lacked them, making it difficult to ensure compatibility across platforms and applications.