IBM 5155 Manual To Operations page 292

66
Hold the option by the top corners and firmly
press it into expansion slot 2, 4, 5, 6, or 7.
Note: Expansion slots 4 and 5 can fit
options that have any overall length of less
than 127-mm (5-in.). Expansion slots 6 and
7 can fit any options that have an overall
length of less than 120-mm (4 3/4-in.).
7 6 5 4 2
4-64 Option Installation