🚀 go-pugleaf

In article <WAYNE.92Dec11164422@backbone.uucp>, wayne@backbone.uucp (Wayne Schlitt) writes:

I certainly appreciate the posting of the 486 information, I have one
clarifiecation to make below.


| Anyway, quoting from my 1990 i486(tm) Microprocessor Programmer's
| Reference Manual from Intel, chapter 21.3:
| 
| ---  start of quote  ---
| 
| 21.3 DIFFERENCES FROM THE 386(tm) CPU
| 
| Very few differences exist between the programming models of the 386
| DX or SX and i486 processors.  The i486 processor defines new bits in
| the EFLAGS, CR0, and CR3 registers, and in entries in the first- and
| second-level page tables.  On the 386 processors, these bits were
| reserved, so the new architectural features should not be a
| compatibility issue.


| 21.3.3 New Instructions
| 
| There are three new application instructions:
| 
| *  The BSWAP instruction
| 
| *  The XADD instruction
| 
| *  The CMPXCHG instruction


| That's the entire section on the differences.  You have to go look at
| other parts of the manual to find out what the details are, but
| basically they come down to this:
| 
| 
| The BSWAP instruction is useful for change the byte orders to/from little
| endian <==> big endian.  
| 
| 
| The XADD and CMPXCHG instructions are useful for implementing
| semaphores in multi-processor systems.  Not something a normal
| application would have much use for.

  Well, I guess I have a little problem with that... both UNIX and
Windows support shared memory and allow it to be used for IPC. Having
solved some access order problems in UNIX with semiphores, I could
appreciate a lower overhead way to do this, and I suspect that windows
programmers could alos use a better solution to this problem.

  This is in user space, although I will not argue that applications at
this level of complexity are "normal" (or at least they're not typical).


| all and all, there are _very_ few real differences between the 386 and
| the 486.
| 
| -wayne

-- 
bill davidsen, GE Corp. R&D Center; Box 8; Schenectady NY 12345
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