Bit Slice ALUs
It was possible to manufacture smaller like 4 or 8 bits fixed point ALUs on a single IC chip. If these chips are constructed as expendable types then employing these 4 or 8 bit ALU chips we can make 16, 32, 64 bit array such as circuits. These are known as bit- slice ALUs.
The basic benefit of such ALUs is that these ALUs can be designed for a desired word size. More details on bit-slice ALUs can be attained from further readings.