Yes... bleed air is taken from the engines and run forward to the 4 turbo compressors and then to the packs. The 70 series planes did away wit the turbo compressors and just used bleed air to pressurize the cabin. On the 70 series you will see the 4 turbo compressor inlets blocked. The center inlet is for air used to cool the pack heat exchangers.
There was also a conversion for the 54/55/61 series as well in the 90's called the NASI system which also did away with the turbo compressors. But it never worked correctly. Crews got sick from oil contamination entering the cabin. Some crews refused to fly the planes with the NASI system.
's required a lot of maintenance and failed fairly often. I scremed like a little girl when one exploded on us. It's located right below the pilots feet. It was loud. You could tel lwhen one was ready to fial on your pre-flight. The overboard TC
turbine discharge along the fuselage would be covered in oil.
[Edited 2011-11-10 13:30:39]