[rescue] Perverse Question

Carl R. Friend crfriend at rcn.com
Sun Jun 15 18:25:06 CDT 2003

   Dave McGuire writes:

> On Sunday, June 15, 2003, at 06:26 PM, Carl R. Friend wrote:
> >    I know for a fact that some of the machines under my charge
> > at work run frighteningly hot (better than a 40 degree rise from
> > air intake to exhaust) and I'm sure won't have terribly long
> > lives.  This does not make me happy.
>    Wow...40 degrees?!

   It may not be *that* much, but it is rather alarming to walk behind
the rack where two of the machines are located and have a very "hot"
spot in an otherwise air-conditioned room.  I'm guesstimating that
the exhaust temperature is around 115 (F) or so.

>    I seem to recall having heard that parts of the P-IV are 
> asynchronous, but I'm not sure; can anyone comment on this?  I'd like 
> to find out once and for all.

   If you hear anything, please post.  I'm curious as well.

   I remember reading a trade rag of some sort touting "Asynchronous
Logic - The Wave Of The Future" a little while ago.  How soon we,
as a species, forget....

> >    I don't regard the genesis of the x86 line to lie with the 8080 and
> > its progeny.
>    But it certainly does.  We can ignore that, though, and the point 
> still stands...see below.

   Similar assembler op-codes do not make a direct descendent.  Any more
than the Interdata Model 3 was a direct descendent of and IBM S/360.

>    The 11/780 and the 8086 both shipped in 1978, though I don't know the 
> months offhand.  The 8086 is a rather direct extension of the 8080/8085 
> architecture...The VAX shares some architectural features with its most 
> direct predecessor, the PDP-11, but nowhere near enough to be called an 
> extension of the architecture.

   I'll concede the latter point, although the 11/xxx machines did
(damned near typed "dud" there) have "compatibility mode" built in.

>    Even at the hardware/implementation level...a complete 8080-based CPU 
> consists of three chips: the 8080 CPU, the 8224 clock generator, and 
> the 8228 system controller and bus driver.  A complete 8086-based 
> system consists of an 8086 CPU, an 8284 clock generator, and an 8288 
> system controller and bus driver (the latter of which is admittedly 
> optional for the 8086).  While they're not binary-compatible, 8080 vs. 
> 8086 assembly code is nearly directly upward compatible.

   This is a common thing.  Usually no microprocessor stands alone;
they need a certain amount of "glue" to bind them into a system.  A
few vaguely similar part numbers and identical assembler op-codes do
not make for a properly proveable "parentage".  (See above for the
Interdata bit.)

   All that bile aside, however, I'm sure that the 8080/8085 strongly
influenced the design of the 8086.  But to call the 8086 a direct
descendent of the 8080 seems, to me, to be a bit of a stretch.  To
me a "direct descendent" is more akin to the PDP-1, PDP-9, and PDP-15
lineage of machines, or the entire Nova/Eclipse line.

| Carl Richard Friend (UNIX Sysadmin)            | West Boylston       |
| Minicomputer Collector / Enthusiast            | Massachusetts, USA  |
| mailto:crfriend at rcn.com                        +---------------------+
| http://users.rcn.com/crfriend/museum           | ICBM: 42:22N 71:47W |

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