| 摘要 |
<p>A prefetch operation greatly reduces the amount of delay between the transmission of a peripheral device request and the receipt of an I/O card acknowledge for peripheral read data, for example in a network printer environment where the amount of time required to transfer print data from an I/O card to a printer is reduced which, in turn, reduces the amount of time required for the printer to process a print job. The communication protocol between a peripheral device and an I/O card is typically based on a packet data structure, which consists of a header that contains the starting address of the buffer, the data length, and maximum data length of the packet buffer fields which are used for the information transfer between the I/O card and peripheral device; and a buffer for transferring data or messages between the peripheral device and the I/O card. The prefetch operation reduces the possibility of shared memory contention by prefetching the next requested data. The next data request is predictable because the packet resides sequentially in the shared memory. The prefetch operation also reduces memory access time for a peripheral device read request when the data are available from a prefetch buffer, such that the access time for a peripheral device read request from the prefetch buffer is relatively short compared to a read request from the shared memory. <IMAGE></p> |
