In the deeps of time, the AMS distributed mathematical symbol fonts called msxm and msym; these fonts were designed using the original (SAIL) version of Metafont and for a long time after the demise of that system were only available as 300 dpi bitmaps.

Eventually, the symbols were re-implemented using ‘modern’ Metafont in fonts called msam and msbm. The virtual fonts of this bundle implement the encoding of the old fonts using the glyphs of the new fonts, and can be used as drop-in replacements in documents (and even when processing DVI files).