Yokemate of Keyboards
Posts: 4955 from 2009/1/28
From: Delaware, USA
>> The address space between 1.5 and 2.0 GiB is used to map and access the memory
>> of on-board and expansion hardware. That's why the OS can't use it as system RAM
>> and it's also why 32-bit addressing would give us access to 3.0 to 3.5 GiB
>> system RAM instead of the entire 4 GiB.
> True, but I'm not even considering moving mapped I/O (which could be placed anywhere
> in the 32bit map).
Huh? Where would you place the mapped I/O on a 32-bit system if not in the upper address space between 3.0/3.5 GiB and 4.0 GiB? I don't think there are options.
Actually it can be done anywhere Andreas.
You might want to look at how some Z80 systems do it, it can really get strange there.
But no, there is no restraint on where to map I/O.
At the top of memory is a common spot, but hardly a requirement.[ Edited by Jim 28.08.2015 - 13:45 ]
"Never attribute to malice what can more readily explained by incompetence"