System for reducing bus overhead for communication with a network interface

The present invention provides a method and an apparatus for transferring data between a computer system and a network interface card that avoids virtual-to-physical address translations. The computer system allocates blocks of memory during system initialization for storing data in transit between the computer system and the NIC, and the physical addresses of these blocks of memory are stored in a table on the NIC. Consequently, address conversion is performed only once, when the memory is allocated. When a request to transfer data to the NIC is received from the upper layers, the device driver copies the data from the upper layers into the next available memory block. The device driver then formats a command and passes it to the NIC for processing. Data transfer commands are communicated to the NIC through a packet descriptor command (PDC), which is a 32-bit value subdivided into fields that completely describe the data transfer operation. The PDC contains a small ordinal value that indexes a table in the NIC, which includes a set of physical addresses of buffers preallocated by the computer system in the computer system memory. These buffers are used for storing data in transit to the NIC. The PDC also contains the length of the buffer to be copied to or from the NIC. The present invention also allows for multiple packets to be formatted into buffers and then subsequently transferred to the NIC in a single I/O operation.