STL internals: deque implementation

Question

I am using a std::deque for storing a large collection of items.
I know that deques is implemented as a list of vectors. The size of those vectors cannot be set but I wander what is the algorithm for choosing that size.

Answer 1

deque is implemented as a vector of vectors (a list of vectors would impede the constant time random access). The size of the secondary vectors is implementation dependent, a common algorithm is to use a constant size in bytes.