SDB is a symbolic debugger for C programs. It may be used to examine their files and to provide a controlled environment for their execution. SDB was first introduced in UNIX/32V. The authors(s) of the original version are unknown, but a second version was created from scratch in 1988 by Brian Russell and David Weatherford.
Sdb (debugger) Wikipedia
SDB is a minimal debugger, that can only debug C programs compiled in COFF format with debug options. The later version (1988) was capable of reading DWARF debugging information.SCO OpenServer(TM) Programming Tools Guide - SDB