Computer Architecture and Organization, 3rd edition, provides a comprehensive and up-to-date view of the architecture and internal organization of computers from a mainly hardware perspective. With a balanced treatment of qualitative and quantitative issues. Hayes focuses on the understanding of the basic principles while avoiding overemphasis on the arcane aspects of design. This approach best meets the needs of undergraduate or beginning graduate-level students.
This along with Computer Organization and Architecture by William Stallings, are excellent resources for understanding not only the mechanics but the context of modern computing.