An automatic washer coordinates the stages of the cycle. In a semi-automatic twin-tub washer, clothes are washed in one tub and moved to another to remove water by spinning.
Two ways to organize the same load of laundry
In an automatic washer, the control system can manage filling, washing, draining, rinsing, and spinning once the program is set. In a twin-tub model, the user steps in between operations and must handle filling, draining, or moving the clothes depending on the design. The exact sequence cannot be inferred from the number of controls.
As an example of this distinction, Samsung India describes its automatic and semi-automatic formats. The capacities and features in that lineup do not apply to all brands.
Water and moving the laundry
Some semi-automatic models allow manual filling; others require specific connections or limits. Draining may be by gravity or by pump. A hose set up like the one on an automatic washer with a pump can prevent a gravity-fed tub from draining.
The spin basket may hold less laundry than the wash tub. As a result, one washed load may require several extractions. The capacity data should be read by function, using dry laundry as the reference when that is how they are stated.
Practical consequences
With an irregular water supply, what matters is which operations the manual allows without continuous pressure. With limited time to monitor the cycle, what matters is how many interventions the load requires. Spinning removes water but does not replace thermal drying.
Two tubs meant for washing and spinning are not the same as two modules that wash simultaneously. That distinction avoids confusing productivity with function.
Before planning a load, confirm who controls each stage: the machine, the user, or both.