Computers and heat density

[Don]

Paul Heller wrote:
>> Tasks that used to (meaning 20 or 30 years ago) used
>> to require a single PDP-8 or PDP-11 class minicomputer now use dozens
>> to hundreds of PC-clone's to do the same functions.
> 
> You mean a single computer with lots of terminals or teletypes, or 
> punched card machines.
> 
>> : WHY DOES IT TAKE 100 COMPUTERS TO DO WHAT
>> A SINGLE COMPUTER USED TO DO?
> 
> We could go back to secretarial pools and reduce the number of 
> computers. Or we can go back to the days of timesharing and give up all 
> the wonderful user oriented capabilities that a modern UI offers, but if 
> you include the end terminals in the comparison then it was not really a 
> single computer in my mind.
> 
> Does anyone know the power difference of the iMac I am typing on right 
> now vs. an old IBM 3279 terminal (which, by the way, was connected to an 
> incredibly inefficient IBM mainframe with a room full of spinning disk 
> machines)? Or the cost of an old Dec terminal? I'm curious how much 
> additional power I am really consuming.
> 
> The IBM 3080 that I worked on in 1983 supported a few hundred users. It 
> gobbled electricity. I bet if you added the mainframe and all the 
> supporting equipment for it (network controllers, terminals, DASD, 
> printers, etc.), 300 modern PCs are cheaper. But this is merely a guess 
> on my part. Personally, I would like to see real figures before I could 
> buy in to your argument.
> 
> To me, the problem is merely expansion. Millions and millions of users.

Well, figure each of those 300 (?) mainframe users was sitting at
a terminal -- that draws power.  For the sake of a 0th order argument,
assume the terminal draws the same amount of power as the *monitor*
in a modern machine (arguably, some -- electromechanical? -- may
draw less; some old VDU's might draw *more* since they rarely
had energy efficient designs, screen savers, etc. and LCD's
probably draw less than any of the older "terminals"... but,
let's ASSUME it's a wash.).

Now, you have the power consumed by that mainframe and peripherals
to offset the power consumed by 300 (?) modern computers.

*If* they each pulled 100W off the mains, that gives the
mainframe 30KW to work with.  A typical USA residence can
burn 20KW before the service breakers trip (100A * 2 legs).
That sure seems like a *lot* of power ... just how much
does a washing machine disk drive assembly draw?  1000W?
And, how many are "required" to support those 300 users?

Note that some modern machines draw less than 100W.  But,
many also draw considerably *more* (e.g., 400W power supplies
in gamer PC's).

Again, just a zeroth order estimate but it doesn't look like
a lead pipe cinch for either case  :-/