tailieunhanh - MEMORY, MICROPROCESSOR, and ASIC phần 8

The và DCC phân vùng của một mạch đơn giản là thể hiện trong hình. . Như đã thấy trong biểu đồ, DCC là tương tự như cửa cho các tế bào điển hình như biến tần, NAND và NOR cửa. Đối với các cấu trúc phức tạp hơn như chốt, một hình duy nhất (điều này tương ứng với thử nghiệm đầy đủ), | 11-8 Memory Microprocessor and ASIC back to memory. The memory system is constructed of basic semiconductor DRAM units called modules or banks. There are several properties of memory including speed capacity and cost that play an important role in the overall system performance. The speed ofa memory system is the key performance parameter in the design of the microprocessor system. The latency L of the memory is defined as the time delay from when the processor first requests data from memory until the processor receives the data. Bandwidth is defined as the rate which information can be transferred from the memory system. Memory bandwidth and latency are related to the number of outstanding requests R that the memory system can service R Bandwidth plays an important role in keeping the processor busy with work. However technology trade-offs to optimize latency and improve bandwidth often conflict with the need to increase the capacity and reduce the cost of the memory system. Cache Memory Cache memory or simply cache is a small fast memory constructed using semiconductor SRAM. In modern computer systems there is usually a hierarchy of cache memories. The top-level cache is closest to the processor and the bottom level is closest to the main memory. Each higher level cache is about 5 to 10 times faster than the next level. The purpose of a cache hierarchy is to satisfy most of the processor memory accesses in one or a small number of clock cycles. The top-level cache is often split into an instruction cache and a data cache to allow the processor to perform simultaneous accesses for instructions and data. Cache memories were first used in the IBM mainframe computers in the 1960s. Since 1985 cache memories have become a standard feature for virtually all microprocessors. Cache memories exploit the principle of locality of reference. This principle dictates that some memory locations are referenced more frequently than others based on two program properties. .