"Terry Coombs" wrote

| It is a limitation of 32 bits, applies more or less equally to any OS.
|
| Thanks , I did download a 64 bit version of Ubuntu 16-04 LTS earlier just
| in case .


More specifically, it's a limitation in addressing.
Stored data in RAM is stored at a memory "address".
Those addresses are critical and ubiquitous in
system functions. To send or receive data from the
system an address pointer is often required. A 32-bit
OS uses a 32-bit "long" integer for those pointers.
It's a 32-bit OS because a 32-bit/4byte integer is
the common currency for data.
So the limitation is simply that a number can't be
specified beyond about 4 billion. There's no way to
point to data stored in RAM at the 5 billionth byte.

Allowing for some sharing of RAM for graphics, that
often works out to about 3.2 GB addressable RAM.