Re: LINUX is obsolete Linux Inside
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Re: LINUX is obsolete

 In article <12605@star.cs.vu.nl> ast@cs.vu.nl (Andy Tanenbaum) writes:
 >In article <1992Jan29.141212.29636@epas.toronto.edu> meggin@epas.utoronto.ca (David Megginson) writes:
 >>
 >>Why does the
 >>Intel architecture _not_ allow drivers to be independent programs?
 >
 >The drivers have to read and write the device registers in I/O space, and
 >this cannot be done in user mode on the 286 and 386. If it were possible
 >to do I/O in a protected way in user space,
 
 [[We must be talking about protected mode]] *THIS IS UNTRUE*
 
 The Intel architecture supports independent tasks, each of which can be
 given a "i/o privilege level". The convenient approach, used by iRMX(?), is
 to "build" a load image ("root" device driver, kernel, MM and FS). Once
 booted, these could be replaced by loadable tasks from disc (or network...)
 and given a suitable privilege level.
 
 The '386 additionally allows each task to have an "i/o permissions bitmap"
 which specifies exactly which ports can be used.
 (See "80386 Programmers Reference Manual", chapter 8)
 
 >                                            all the I/O tasks could have
 >been user programs, like FS and MM.
 
 Do you really mean "user programs" and not "separate tasks" ??
 
 Separate tasks, possibly privileged, I'll agree with.
 
 User level programs may be ok for teaching operating system principles, or on
 toy computers :-)  But a "production" system?  Not on my machines!
 
 >Andy Tanenbaum (ast@cs.vu.nl)
 
 joe.
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 joe@jshark.rn.com
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