A 32K print buffer has little or no effect when used with the Macintosh
printing anything but text in Draft quality. For instance, if all MacWrite
needed to do was send out a single byte of information for each character
that it wanted to print, a serial buffer with 64K of memory would be able
to receive and hold at least 20 pages of material and free up your
Macintosh for other work while the printer was busy. If you're content
with selecting Draft quality from the Print Dialog box, such a buffer
device should work just fine. In Draft mode, the ImageWriter, acting like
most serial printers, simply receives a sequence of single character codes
(the ASCII set), one code for each character that is to be printed. For
example, a typical MacWrite page of Geneva 12-point font will rarely
exceed 3000 characters. The ImageWriter II optional buffer can handle the
printing of up to 10 such pages in Draft Quality mode.
Because of the way the Macintosh sends information to the printer in the
Standard and High Quality modes, a 32K buffer would not be large enough to
hold even one page of information. To produce print quality better than
Draft, the ImageWriter must receive much more information than simply a
one-byte code per character.
Say you select High quality text from the Print dialog box and Tall
Orientation form the Page Setup dialog box. This means that the
ImageWriter will be printing 160 dots per inch horizontally and 144 dots
per inch vertically. For an 8 inch by 10 inch printed page, the Macintosh
has to send enough information to the printer so that it can image
(160*8)*(144*10) or 1,843,200 dots. Each dot to be printed takes a bit of
information to tell the printer whether the dot is supposed to be black or
white. The printer can receive this information in 8-bit words, which,
divided into the 1,843,200 dot/bits of the page, results in 230,400 words
of memory (approximately 225K) needed in a print buffer device for storing
even one page of MacWrite information. A buffer that could handle a
20-page document would need 2 megabytes of memory.
Some third party buffers have enough memory to make them effective print
buffers on the Macintosh.