How free42's memory works?

[slabco]

unlike hp42s which has fix memory if I creat a 10*10 matrix the memory of hp42s becomes less, if I create a 1000*1000 matrix with free42 the memory is still very large and may become more sometimes. When I do some calculate with large matrix free42 quits sometimes. How free42's memory works ? It may work with mobile phone's RAM and storage memory. The calculator only has one kind of memory. so pepole can calculate how much memory can be used safely.
Who can tell the machanics? How many memory of free42's can be used safely?