Reply to post: Re: Bits of this are really cool

Oracle's Larry Ellison claims his Sparc M7 chip is hacker-proof – Errr...

Warm Braw Silver badge

Re: Bits of this are really cool

Indeed, this is (roughly) how the 360 did memory protection before the days of virtual memory - there were 15 protection keys (plus one for the system) which allowed the memory to be divided into a number of fixed (OS/MFT) or variable (OS/MVT) partitions, each of which could contain a separate program (job step). The hardware compared the protection key of the memory being accessed with 4 bits of the Program Status Word that the OS set to the correct key for the program currently executing.

Unfortunately, 16 isn't a big number...

I'm also not sufficiently familiar with the SPARC architecture to know if the caches use physical or virtual addresses - if they're physical addresses it could be quite complicated to ensure that two processes with pointers to different areas of overlapping shared memory were both allocated the same "colour".

POST COMMENT House rules

Not a member of The Register? Create a new account here.

  • Enter your comment

  • Add an icon

Anonymous cowards cannot choose their icon

Biting the hand that feeds IT © 1998–2019