I am honored and privileged to write the foreword for the fourth edition of this most important book in computer architecture. In the ﬁrst edition, Gordon Bell, my ﬁrst industry mentor, predicted the book’s central position as the deﬁnitive text for computer architecture and design. He was right. I clearly remember the excitement generated by the introduction of this work. Rereading it now, with signiﬁcant extensions added in the three new editions, has been a pleasure all over again. No other work in computer architecture—frankly, no other work I have read in any ﬁeld—so quickly and effortlessly takes the reader from ignorance to a breadth and depth of knowledge.