Subject: Is an MMU necessary?
To: David Maxwell <>
From: Grant Stockly <>
List: netbsd-ports
Date: 07/26/2000 02:27:10
>On Tue, Jul 25, 2000 at 02:53:55PM -0800, Grant Stockly wrote:
>> >There was a discussion some time ago (see for
>> >archives), if I remember properly the conclusion was that most i960-based
>> >systems availanle didn't have an MMU, and so were unusable for an Unix-like
>> >system.
>> What exactly is the function of an MMU and can it be emulated in software?
>An MMU is a Memory Management Unit. Typical MMU functions include the
>ability to reference a Virtual Memory address space, and have the MMU
>trigger an interrupt when a process tries to access something that isn't
>available in RAM at the moment - then you catch that interrupt and load
>the required data and the process can continue. MMUs also provide the
>ability to trap regions of memory so that a process can be denied access
>to memory that doesn't belong to it.
>So no, you can't emulate it in software. If the CPU supported catching
>the operations described above so that software could do some of the work,
>it would arguably have a 'built-in' MMU.

Can you get by without a MMU?