TRIPOS and memory protection

On Tue, Jun 24, 2008 at 08:56:13AM +0200, Eric J Korpela wrote: AmigaDOS itself never used the MMU for memory protection, but there was a tool available _with_ AmigaDOS (first for developers, then for everyone) called "Enforcer" that would set up some basic memory protection between all processes and sensitive parts of the OS. The basic memory protection scheme was to write-protect low mem so a random process wouldn't scribble on $00000000 or $0000004 (reads/writes to $00000000 usually meant that your code was trying to dereference a null pointer - the reaction to which is implementation specific - it's usually safe to treat a null pointer as if it were a pointer to a null (zero-length string), but it's equally valid for the code to puke from trying it; reads of $00000004 are absolutely required on the Amiga because that's how you find all the libraries and system structures. _Writes_ however are very bad and can crash the machine in under a second). I don't think there ever was any attempt to prevent one process from scribbling on another process, though. Enforcer just kept you out of the OS-required area and kept you from accidentally writing to unallocated memory (falling off the ends of buffers, etc). Malicious writes into other process space wouldn't have been stopped. -ethan -- Ethan Dicks, A-333-S Current South Pole Weather at 24-Jun-2008 at 07:30 Z South Pole Station PSC 468 Box 400 Temp -79.4 F (-61.9 C) Windchill -113.8 F (-81.0 C) APO AP 96598 Wind 8.4 kts Grid 21 Barometer 676.1 mb (10776 ft) Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html