location - MIPS Instruction set -

location - MIPS Instruction set -

just quick question while reading: http://www.cs.umd.edu/class/sum2003/cmsc311/notes/mips/format.html

under i-type instruction, says:

"in case, $rt destination register, , $rs source register. unusual $rd not used, , $rd not appear in bit positions b25-21 both r-type , i-type instructions. presumably, designers of mips isa had reasons not making destination register @ particular location r-type , i-type. "

can explain mips isa designers' reasons are?

location mips isa