Nominally, all Hewlett-Packard LaserJet~4–series and newer printers have the same internal fonts: 45 scalable fonts and one bitmapped Lineprinter font. The scalable fonts are available in sizes between 0.25 point and 999.75 points, in 0.25-point increments; the Lineprinter font is available only in 8.5-point size.
The LaserJet font files included with groff assume that all printers since the LaserJet~4 are identical. There are some differences between fonts in the earlier and more recent printers, however. The LaserJet~4 printer used Agfa Intellifont technology for 35 of the internal scalable fonts; the remaining 10 scalable fonts were TrueType. Beginning with the LaserJet~4000–series printers introduced in 1997, all scalable internal fonts have been TrueType. The number of printable glyphs differs slightly between Intellifont and TrueType fonts (generally, the TrueType fonts include more glyphs), and there are some minor differences in glyph metrics. Differences among printer models are described in the PCL~5 Comparison Guide and the PCL~5 Comparison Guide Addendum (for printers introduced since approximately 2001).
LaserJet printers reference a glyph by a combination of a 256-glyph symbol set and an index within that symbol set. Many glyphs appear in more than one symbol set; all combinations of symbol set and index that reference the same glyph are equivalent. For each glyph, hpftodit(1) searches a list of symbol sets, and selects the first set that contains the glyph. The printing code generated by hpftodit(1) is an integer that encodes a numerical value for the symbol set in the high byte(s), and the index in the low byte. See groff_font(5) for a complete description of the font file format; symbol sets are described in greater detail in the PCL~5 Printer Language Technical Reference Manual.
Two of the scalable fonts, Symbol and Wingdings, are bound to 256-glyph symbol sets; the remaining scalable fonts, as well as the Lineprinter font, support numerous symbol sets, sufficient to enable printing of more than 600 glyphs.
The metrics generated by hpftodit(1) assume that the DESC file contains values of 1200 for res and 6350 for unitwidth (or any combination (e.g., 2400 and 3175) for which res~×~unitwidth~=~7620000). Although HP PCL~5 LaserJet printers support an internal resolution of 7200 units per inch, they use a 16-bit signed integer for cursor positioning; if devlj4 is to support U.S. ledger paper (11″~×~17″), the maximum usable resolution is 32767~/~17, or 1927, units per inch, which rounds down to 1200 units per inch. If the largest required paper size is less (e.g., 8.5″~×~11″ or A5), a greater resolution (and lesser unitwidth) can be specified.