Over the past two decades, there has been a huge amount of innovation in both the principles and practice of operating systems Over the same period, the core ideas in a modern operating system - protection, concurrency, virtualization, resource allocation, and reliable storage - have become widely applied throughout computer science. Whether you get a job at Facebook, Google, Microsoft, or any other leading-edge technology company, it is impossible to build resilient, secure, and flexible computer systems without the ability to apply operating systems concepts in a variety of settings. This book examines the both the principles and practice of modern operating systems, taking important, high-level concepts all the way down to the level of working code. Because operating systems concepts are among the most difficult in computer science, this top to bottom approach is the only way to really understand and master this important material.

As we continue to build faster and fast. er computers, their performance is be coming increasingly dependent on the memory hierarchy. Both the clock speed of the machine and its throughput per clock depend heavily on the memory hierarchy. The time to complet. e a cache acce88 is oft. en the factor that det. er mines the cycle time. The effectiveness of the hierarchy in keeping the average cost of a reference down has a major impact on how close the sustained per formance is to the peak performance. Small changes in the performance of the memory hierarchy cause large changes in overall system performance. The strong growth of ruse machines, whose performance is more tightly coupled to the memory hierarchy, has created increasing demand for high performance memory systems. This trend is likely to accelerate: the improvements in main memory performance will be small compared to the improvements in processor performance. This difference will lead to an increasing gap between prOCe880r cycle time and main memory acce. time. This gap must be closed by improving the memory hierarchy. Computer architects have attacked this gap by designing machines with cache sizes an order of magnitude larger than those appearing five years ago. Microproce880r-based RISe systems now have caches that rival the size of those in mainframes and supercomputers.