A magnetic tape drive having a tape drive system for moving magnetic tape, tape read/write and servo system, tape cartridge load/unload systems, I/O communications, memory; and a control system, operates in three modes to conserve energy consumption. A first low power mode powers the I/O communications, the memory, and the control system. If a magnetic tape cartridge is in loaded position in the magnetic tape drive, the second low power mode powers the same as the first low power mode, and additionally powers the tape drive system to apply tension to a magnetic tape of the magnetic tape cartridge. In the first and the second low power modes, the control system operates the I/O communications, the memory and the control system to respond to and execute commands received at the I/O communications if the commands are executable without magnetic tape access. The third, full power mode, is entered if a command received at the I/O communications requires magnetic tape access.