A bit of googling finds this Japanese article, and DeepL does a really impressive English translation, which I am mostly just going to quote, with a bit of corrections.
- 1960: prototype of fully automatic SAPTON typesetting machine announced
- 1962: SAPTON-F numeric-only typesetting machine delivered to Japanse Defence Agency
- 1965: SAPTON-N fully automatic typesetting machine for newspapers announced
- 1966: First SAPTON-N delivered
- SAPTON-P for books and magazines developed in parallel with above
- 1969: First SAPTON-P delivered
- 1969: SAPTON-A system for general printing announced
- SAPCOL-D editing and typesetting software for SAPTON-A, using a PDP-8, developed together with SAPTON-A
- 1970: First SAPTON-A system, consisting of SAPTON-A5260 and SAPCOL-D1,delivered.
From the SAPTON-N on, the SAPTON machines used a high-speed rotating character disk (picture in the link) and apparently some kind of optical transfer mechanism to do the actual printing.
The SAPTON-N3110 was
a fully automatic typesetter that reads CO-59 paper tape, selects the appropriate character from a high-speed rotating character disk with a capacity of 2,304 characters, and types 15 characters per line vertically on a 35mm wide non-perforative roll. The machine prints 15 characters per line in vertical format (the number of characters in a newspaper) on 35mm wide non-perforative rolls.
It had one typeface, one character size for the main text, and a printing speed of 300 characters per minute (equivalent to three times the speed of a fully automatic imprinting machine).
The SAPTON-P was
equipped with a single character disk (with a capacity of 2,880 characters, the character disk can be replaced using a cassette system), image rotation prisms for vertical and horizontal typesetting, four character sizes (10-14Q), and a mono external character insertion device (up to 50 characters). One-sided perforated rolls of 2 to 10 inches wide (7 types) were loaded, and the printing speed was 300 characters per minute.
held 6,400 characters, including six European fonts, a ruby font (smaller Hiragana written atop on Kanji), symbols, and numbers, on two character disks, one in Mincho and one in Gothic, and was equipped with an image rotating prism, six character sizes, and a mono external character insertion device. The SAPTON-A5440 was equipped with four character disks.
Finally, the SAPCOL-D1,
the editing and typesetting software for SAPTON-A, used DEC's PDP-8 minicomputer (16 KB main memory, 64 KB magnetic disk). At that time, minicomputers did not have an operating system (OS) equivalent, so we developed our own OS equivalent program and simple language, including multiple control of I/O devices and memory management including auxiliary storage.
SAPCOL-D1 added to the typesetting functions of SAPTEDITOR-P many processing functions necessary for general printing, such as headings, tabs, mixed typesetting of different sizes, mixed typesetting of Japanese and European text, ruby, separation prohibition, continuous numerals, and selective printing of red correction parts.
That's probably 16 KWords (not KB), or 4 core memory modules for the PDP-8, which was a common size. As for the "magnetic disk" (磁気ディスク), an RK01 stores 256 KBytes (not words, but that's still at least 128 KWords), and a harddisk stores several megabytes, so the "64 KB" is possibly an inaccuracy on side of the author. DEC tapes, which were more common than floppies, stored 184 KWords.
Anyhow, that means fonts were never stored in memory or on other storage, but always came from optical disks in the actual printing mechanism, and not in the copyediting part of the system.