The system also hard to update the image contained in such a huge picturebox.

I also run into this issue, then i rewritten my code, to work on the current picturebox, but i draw the items, that they should appear or not. I use PosX and PosY values, to determine what are the topleft corner of the work-area that is select the items what will be appear.

So i use picturebox that is big as it look alike, i wont use the scrollable picturebox inside a picturebox method.

Windows XP also using system memory on desktop works (GDI), the extended VGA memory (those huge 512/1024 mbyte or more) are only reserved for bitmaps that directx using for texturing the polygons.