"The 707's engines could not supply sufficient bleed air for pressurization without a serious loss of thrust, so the aircraft instead used engine-driven turbocompressors to supply high-pressure air for this purpose. On many commercial 707's the outer port (#1) engine mount is distinctly different from the other three, as this is the only engine not fitted with a turbocompressor."
Not quite true ...
The regulations at the time would not allow engine bleed air as a source for A/C services, so Turbocompressors were installed on engines 2, 3 and 4. (the B720 only has them on 2 and 3)
The Turbocompressors were driven by engine bleed air (cannot remember which stage compressor air was bled from). The bleed air would drive a turbine which inturn turned a compressor (air supply was directly from the atmosphere) that supplied compressed air for A/C services.