Past exam of the year 1 of the computer science course of the University of Oxford / 2013 / Digital systems, linear algebra, introduction to formal proof / 2 / a

Use the MIPS zero register as a write-suppression destination: encode $r_d=0$. There are only 31 stored processor registers, and address zero denotes the constant-zero source rather than a writable storage cell. Its writes are discarded, soThis permits a store to write memory while its unavoidable register file write has no effect. It also implements a no-operation by selecting no memory write and destination zero. The statement that reads of register zero return zero is realized consistently by this standard constant-zero, discard-writes implementation.