Well, don't forget that a DataTable stores 2? 3? versions of the data - original and updated (possibly one other?). It also has a lot of references since it is cell-based, and boxing for any value-types. It would be hard to quantify the exact memory...
Personally, I very rarely use DataTable - typed POCO classes are a much more sensible bet in my view. I wouldn't use an array (directly), though - List<T> or BindingList<T> or similar would be far more common.
As a crude measure, you could create a lot of tables etc and look at the memory usage; for example, the following shows a ~4.3 factor - i.e. more than 4 times as expensive, but obviously that depends a lot on the number of columns vs rows vs tables etc:
// takes **roughly** 112Mb (taskman)
List<DataTable> tables = new List<DataTable>();
for (int j = 0; j < 5000; j++)
{
DataTable table = new DataTable("foo");
for (int i = 0; i < 10; i++)
{
table.Columns.Add("Col " + i, i % 2 == 0 ? typeof(int)
: typeof(string));
}
for (int i = 0; i < 100; i++)
{
table.Rows.Add(i, "a", i, "b", i, "c", i, "d", i, "e");
}
tables.Add(table);
}
Console.WriteLine("done");
Console.ReadLine();
vs
// takes **roughly** 26Mb (taskman)
List<List<Foo>> lists = new List<List<Foo>>(5000);
for (int j = 0; j < 5000; j++)
{
List<Foo> list = new List<Foo>(100);
for (int i = 0; i < 100; i++)
{
Foo foo = new Foo { Prop1 = "a", Prop3 = "b",
Prop5 = "c", Prop7 = "d", Prop9 = "e"};
foo.Prop0 = foo.Prop2 = foo.Prop4 = foo.Prop6 = foo.Prop8 = i;
list.Add(foo);
}
lists.Add(list);
}
Console.WriteLine("done");
Console.ReadLine();
(based on)
class Foo
{
public int Prop0 { get; set; }
public string Prop1 { get; set; }
public int Prop2 { get; set; }
public string Prop3 { get; set; }
public int Prop4 { get; set; }
public string Prop5 { get; set; }
public int Prop6 { get; set; }
public string Prop7 { get; set; }
public int Prop8 { get; set; }
public string Prop9 { get; set; }
}