The X Window System has been in widespread use through releases 3, 4, and now 5 of X Version 11.
Fonts weren't really treated by the X Consortium very well until X11 release 5 (X11R5). In X11R3 and X11R4, the default format used by the X servers was called SNF (server normal format). Basically the font was formatted on disk in such a way that the X server could quickly read and use it (it was basically a memory-dump). The important element of the SNF format is that it was not a portable format: it depended on the architecture of the machine running the server (little endian vs. big endian, for example) and as a consequence you needed different directory structures for different systems on your network. On top of that, several systems vendors implemented their own font format, making font portability even more difficult.
With X11R5, two things changed: the font service protocol was defined as a standard and interoperable way for an X server to obtain fonts (independent of their format, origin, or current location on disk) and the default format for storing fonts was changed from SNF to PCF (Portable Compiled Font). PCF is a format originally developed by DEC. Its primary advantage is that it is not architecture dependent. That is, if you compile a font to PCF format on different systems, then you may end up having two different PCF files, but each system will be able to read the other's file correctly.