26 Apr
2008
26 Apr
'08
10:01 a.m.
Date: Fri, 25 Apr 2008 22:39:29 +0100 (BST)
From: (Tony Duell)
Did very early machines have AC fans? All the later
ones certainly had 12V
DC ones that would be independant of mains frequency, but an AC fan would
run slower on 50Hz and could cause the machine to overheat. Was it really
that marginal (Acutally, given it's the IBM PC [1], I could beleive it
was).
Yes, they did, but the fans were rated for 50-60 Hz operation and
impedance-protected. With the factory, what 62-watt?, PSU, I don't
think it was possible to stuff the thing full enough of drives and
cards to make it overheat (remember too, that there were only 5
slots) to make it overheat. Wasn't the (black) PSU on the original
PC fitted with red tamper-telltales stuck on along the edge of the
PSU clamshell? I can't remember exactly, but I think it was.
As this was an IBM product, I fully expected that there would have
been some provision for changing the AC input voltage. Certainly
other personal computers of the time had the feature, and this wasn't
supposed to be a product from "Fred's Personal Computer and Aluminum
Storm Door Company". One expected a high level of engineering from
IBM.
[1] When I got my first IBM PC-family machine (a 5160), I took it to
bits
(what a suprise) and sat down with the TechRef. Every few minutes I'd
exclaim 'They did WHAT???' as I found aother it of misdesign...
I never understood the design that featured a complete lack of a
clear airpath between the plug-in-cards. They must not have been
expecting very much expansion.
The MDA card was the most bewildering experience to work through--
circuit traces headed off to nowhere, ICs that seemed to perform no
function. Perhaps it was designed for graphics operation originally
and not completed and rushed to market.
Similarly, one suspects that the printer port must originally have
been intended as a full bidirectional design and then changed at the
last minute--on both the MDA and the printer adapter, all the
necessary circuitry was present for bidirectional operation. Cutting
and jumpering a single trace was all that was needed.
All in all, for as long as the 5150 was in the rumor mill, one would
have expected a better thought-through design from IBM.
Some aspects were pretty good--the original keyboard was very good;
the casework with rolled edges was also notable, although the case
design itself was questionable (particularly in mounting/unmounting
disk drives). Many Taiwanese vendors improved on the case design by
incorporating a hinged lid; I don't know if that met with Part 15
requirements, but it was very convenient.
Cheers,
Chuck