Further to FE Hoppy's note -
707/DC-8 etc. as originally certified were required to have air NOT supplied directly from the engine airflow. Instead, turbo-compressors (a la turbosuperchargers) tapped engine bleed air to spin a turbine, which in turn spun a compressor which pumped up fresh outside air for pressurizing the cabin. On 707/720 aircraft these are housed in a cowl bump over the nacelle inlets, on two or three of the engines.
DC-8 Super 70 conversions use engine bleed air a la widebodies and later.