HP PCL/PJL reference (PCL 5 Printer Language) - Technical Reference Manual Part II

EN Performance 24-11
Note The page protection feature is available only with additional optional
memory on many HP LaserJet printers. (One exception is the
LaserJet 4 printer, which supports page protection for letter-size
paper in 300 dpi mode with the standard 2 Mbytes memory.) Refer
to the appropriate User’s Manual for specific memory requirements.
The Page Protection feature can be used to prevent possible
ERROR
21
conditions. ERROR 21 is reported when data is too complex for
the printer to process concurrent with actual physical printing. A
frequent cause of
ERROR 21 when printing graphics is that the
program sends commands to print a single point many times during
the page run.
Page protection can be set for letter, A4, or legal sized pages. Set
page protection for the page size most often used.
I/O
The Parallel (Centronics) I/O has higher throughput than the
RS-232C serial I/O. While text processing may not benefit from a
faster I/O, raster graphics processing and soft font downloads will
usually benefit from increased I/O throughput.