1. A heat sink for a plug-in card, comprising:a first part secured to a surface of the plug-in card, the first part having a first heat radiating fin extending along a first direction, the first direction being perpendicular to the surface of the plug-in card;
a second part coupled to the first part and being movable relative to the first part in the first direction such that the heat sink has different heights with different overlaps between the first part and the second part, the second part having a second heat radiating fin corresponding to the first heat radiating fin and extending along the first direction; and
a first transmission mechanism pivotably coupled to a side wall of the plug-in card via a shaft oriented along a second direction perpendicular to the first direction, wherein the side wall extends along a third direction perpendicular to the first direction and the second direction, the first transmission mechanism comprising a first end coupled to the shaft and a second end coupled to the second part of the heat sink,
wherein one of:
the first heat radiating fin and the second heat radiating fin are arranged in a staggered manner in the first direction and are in a thermal contact with each other, and have an offset in between in the second direction; or
the first heat radiating fin and the second heat radiating fin are aligned with each other in the first direction, and at least a portion of the second heat radiating fin is receivable in the first heat radiating fin and is in thermal contact with the first heat radiating fin.