A subtract with borrow (SBB) instruction will compute a−b−C = a−(b+C), while a subtract without borrow (SUB) acts as if the borrow bit were clear. The 8080, 6800, Z80, 8051, x86 and 68k families (among others) use a borrow bit.
A subtract with carry (SWC) instruction will compute a−b−C = a−(b+C), whereas a subtract without carry (SUBW) acts as if the carry bit were nullified. The 8080, 6800, Z80, 8051, x86 and 68k families (among others) utilize a carry bit.