Methods, devices, subsystems, systems, and techniques for managing data transmissions with selectable modes are provided. In one aspect, a computing system includes: a host system, peripheral component interconnect express (PCIe) devices, and a PCIe controller having a PCIe switch coupled between the host system and the PCIe devices. The PCIe controller is configured to: set a mode of the PCIe switch to be a first PCIe mode using first mode data, and transmit, under the first PCIe mode, first data between the host system and at least one of the PCIe devices, and set the mode of the PCIe switch to be a second PCIe mode using second mode data, and transmit, under the second PCIe mode, second data between the host system and one or more first PCIe devices and third data between the host system and one or more second PCIe devices.