The present invention discloses re-configurable data transmission ports with data-integrity transaction controlling unit in a computerized computer and the method for performing the same. The controlling unit further includes a port-configuration detecting mechanism and a buffer-configuration subunit. The port-configuration detecting mechanism can inspect configuration status of all of the first ports on variance of data transmission bandwidths, e.g. "merge" or "spilt" status. The buffer-configuration subunit upon different configuration status of each first port configures each retry buffer. When a specific first port is configured on "merge" status, the buffer-configuration subunit can follows up to configure the retry buffer owned by the specific first port and the retry buffers owned but disused by the other first ports to constitute a buffer group with merging of storing spaces of said configured retry buffers. The controlling unit sequentially backs up a data on the buffer group upon the data is transmitted from the specific first port to a corresponding second port.If the specific first port receives a non-acknowledge (NAK) message or nothing from the corresponding second port within a specific time, the data is retransmitted from the buffer group to the corresponding second port. If the specific first port exactly receives an acknowledge (ACK) message from the corresponding second port, the data is cleaned from the buffer group.