Which steering system is characterized by having a separate hydraulic pump?

The correct choice regarding the steering system characterized by having a separate hydraulic pump is semi-integral power steering. In this type of system, the hydraulic pump provides assistance that helps reduce the effort required by the driver to turn the steering wheel, while still allowing for a more traditional mechanical linkage to maintain direct control over the steering system.

In contrast, manual steering does not use any hydraulic systems; instead, it relies solely on mechanical components for steering. Integral steering systems possess an integrated hydraulic assist within the steering gear itself, meaning they do not require a separate hydraulic pump; rather, they are driven by the engine and do not stand alone. Electric steering systems utilize electronic motors to provide assistance, eliminating the need for a hydraulic pump altogether.

Thus, the separate hydraulic pump is a defining feature of semi-integral power steering, which distinguishes it from other steering mechanisms mentioned.