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From: thad@btr.btr.com
Newsgroups: comp.sys.amiga.hardware
Subject: The Fanning of the Amiga
Message-ID: <3004@public.BTR.COM>
Date: 10 Jun 91 01:17:46 GMT
Sender: thad@public.BTR.COM
Organization: BTR Public Access UNIX, Mountain View CA
Lines: 91

In comp.sys.amiga.games, xanthian@zorch.SF-Bay.ORG (Kent Paul Dolan) wrote in
article <1991Jun9.122639.16244@zorch.SF-Bay.ORG>:

|  rjtatz@magnus.acs.ohio-state.edu (Robert J Tatz) writes:
|
| > These games got wiped out over 5-6 month gap.  One got "jellied" or
| > something, so the darn problem is having to use the original.
|
| As to the "jellied", that was what it looked like after a second instar
| cockroach tried to take a merry-go-round ride on one of my floppies;
| smeared the little sucker 1/4th of the way around the disk as a jelly.

Kent's tale of "Jelly Floppies" brings up a hardware issue that's been a pet
peeve of mine for decades: incorrect "fanning" of computers.

Background:  for years I've been wondering why spiders seek out and enter
the floppy drive and/or tape-drive ports on most my computers.  And for years
I've lamented the excessive need to open the computers every 3-6 months or so
and clean out the dust bunnies, hair, etc. that tends to accumulate inside.

So how are those two items related?  Air flow paths.

Informal (read: summertime beer-drinking-related :-) studies have shown that
many bugs (the firmware, living/breathing kind (and, yes, I do know that
spiders are arachnids and not "bugs", so what?  After squishing both, spiders
and bugs appear the same. :-) ) tend to follow/track/stalk air currents that
diverge from the ambient norm, air patterns such as those resulting from
non-weatherstripped house doors, partially-open windows, poorly-insulated vent
systems, AND those generated by computer fans. 

Dust, lint, smoke and other atmospheric contaminants ALSO tend to follow the
same air currents.

The PROBLEM is that most computers have fans that evacuate inside hot air by
sucking the air out.  This means that outside "cool" air enters the computer
via any openings, typically floppy drive slots; accompanying that outside air
will be dust and other contaminants (followed quickly by spiders and bugs :-)

The SOLUTION is to create a positive (higher than ambient) air pressure inside
the computer which effectively blocks airborne contaminants.  Air currents will
flow from a high-pressure area (inside the computer) to the low-pressure area
(outside the computer); this technique is commonly used for "IC clean rooms"
and for hospital surgical theatres.

To effect the SOLUTION for a computer basically requires a fan to blow inwards.
Because only clean air should enter the computer, a filter is needed at the
fan's intake.  (And that filter should be removeable and cleanable)

Some companies do design their computer cases for positive pressure, and the
insides will and DO remain clean for years, thus preventing a dust-blanket
buildup.  (Such dust-blankets trap and retain heat, and heat is the enemy of
all electronic equipment).

For those who remember my SCSI talk at BADGE several years ago during which
I demo'd the Fujitsu tape drive in a (surplus) IBM case, that case epitomized
a properly-designed and filtered positive pressure enclosure for computer
equipment.  (And, no, that was NOT an IBM-PC case, it was a case from one of
IBM's professional line of computers; it could hold two full-height 5-1/4"
HDs behind which are mounted the power supply, fan and externally-accessible
filter).

As a prime example of BAD design which causes me much grief, I point to the
external HD/tape-drive case of the Sun 3/60 at my office: two fans sucking air
out by blowing through "window-screen" filters.  Besides that design's evils
of sucking in dust across the tape head and the fact the screens quickly clog
preventing air flow, the screens are WELDED to the case making cleaning a very
difficult chore.  If those screens were omitted, air, albeit dirty, would still
flow and the box would not overheat (which it does tend to do due to lack of
air flow).  [HINT: do NOT operate such computers near carpeted areas, and keep
paper, pencil erasings, tissue (e.g. Kleenex), hairy people, etc. away from
the machine! :-) ]

Point of all this being: a relatively simple parts relocation (probably not
even requiring external case modifications) could add an additional aura of
professionalism to the Amiga and increase reliability which IS important for
those systems operated 24 hrs/day.

And a "tip" from mainframe systems would be the use of an air-flow sensor
along with an overtemperature (thermal) switch; a "trigger" from either sensor
could, say, throw up a requester or ALERT (for AmigaDOS) or initiate a proper,
automatic, sequenced shutdown (for Amiga UNIX).

In the absence of air-flow sensors, it is still possible to design a "cooling"
system that will move air (even if the filters ARE clogged) using inexpensive
pressure-differential-sensing ducting flaps (which appear like the vacuum-
operated "doors" used in automotive passenger-area air-conditioning systems).

Comments on this topic are invited, and suggestions how to retrofit existing
Amiga systems are welcome.

Thad Floryan [ thad@btr.com (OR) {decwrl, mips, fernwood}!btr!thad ]