The hardware font available on the Charactron tube was primarily aimed at microfiche output so was small in size. In consequence there was a need to generate software fonts for use on hardcopy and also films.
The main fonts were:
This is an example of a letter in the largest of the three Bell Labs fonts:
The fonts included both upper- and lower-case Roman letters in three sizes, lower- and upper-case Greek in two sizes, digits in three sizes and various mathematical symbols. The SC4020 draws short vectors (less than 64 pixels in X and Y) by a single instruction so making the font up of many short lines is the most efficient. SC4020 lines are just over two pixels wide under normal set up. The three fonts were in the ratio 1 : 1.5 : 2. The largest font size was designed for titles and the medium one for normal text.
Bell Labs provided the fonts to other SC4020 sites as a deck of tightly packed cards. For example, the largest font Q was defined by 11 cards:
3 722912 114 114 118 218 221 421 423 623 624 824 825112511251525152418 3 722924182320232021222122182418241225122510251025 824 824 522 522 320 ....
The first two columns define the font number (3), columns 4-6 the character code (72), columns 7-8 the width of the character and 9-16, 17-24, ..., 65-72 define 8 vectors. In the example, the vectors are:
X1 Y1 X2 Y2 12 1 14 1 14 1 18 2 18 2 21 4 21 4 23 6 23 6 24 8 24 8 25 11 25 11 25 15 25 15 24 18 24 18 23 20 23 20 21 22 21 22 18 24 18 24 12 25 12 25 10 25 10 25 8 24 8 24 5 22 5 22 3 20
This is the outer line of the Q clockwise from the top.
As shown at the bottom, if the line thickness is increased to the thickness of the SC4020 hardware vectors, the character glyph fills in so that it looks like a filled area even though it is made up of many short vectors.
This font had a basic size 20 × 10 raster units ( approximately the size of the SC4020 hardware characters). It was made up of single straight lines. An example of the font can be seen at the start of the GROATS film.
This font was particularly useful for titles in film. It was defined by the BBC and presented to the Laboratory on two very large white boards. Atlas staff digitised the drawings to create the font. It was used in numerous films including the Open University Mathematics Films. Its main advantage was that it could be drawn at various sizes and still looked respectable.
