Max_server_memory affecting plan.

Hello,

I am experimenting on TPCH 10-GB data, and I came across following :

Keeping Max_server_memory=128MB, the plan chosen by the optimizer involves Nested loop join.

Keeping Max_server_memory=4096MB, the plan chosen by the optimizer involves Hash Match join.

Can, you explain me how changing max_server_memory is affecting the choice of plan, one more thing to specify is that, I am talking about estimated execution plan only, i.e. these mention plans are estimated plans and not actual plan.

Looking forward to some helpful explanation!