The font-selection scheme (FSS) that LaTeX normally uses is somewhat limited. This is known as the Old Font Selection Scheme (OFSS). A new scheme has been written and distributed by Frank Mittelbach and Rainer Schöpf---the so-called New Font Selection Scheme (NFSS). When you run a file with REVTeX you will see a message telling you which FSS you are running on, right after the file aps.sty is read in. Several font problems have been addressed in REVTeX itself so it is not very important which FSS you use, since REVTeX has been written to run equally well on either FSS. It should be said that, in general, an NFSS installation is more capable than an OFSS installation.
At this time we are only supporting the NFSS if it is used with
oldlfont.sty. This makes the NFSS use the same font-selection macros as the
OFSS. If you use the NFSS and ${\bf ABC}$ gives boldface letters,
then you are using oldlfont.sty. Here is the output of ${\bf ABC}$:
.