🚀 go-pugleaf

Scott Colwell states (correctly) that quartz crystal oscillators (TTL-crystal o
scillators) run out of steam (read: price-performance benefits) around 80 MHz.
 On the other hand, clock division is very cheap, even if a little ECL is neede
d, and SAW-based quartz oscillators start around 300 MHz (i.e. garage door open
er xmitter oscillators.  So, the availability of oscillators doesn't limit the
CPU speed.  Furthermore, having a 100MHz oscillator and 2x divider in a sheilde
d box will not cause RFI any more than the inherent harmonics of a square wave
at most of the popular CPU speeds.
   What really limits CPU speed is heat dissapation and the 5V standard.  Curre
nt research in the microwave generation of diamond thin films from methane will
 be a big factor in future high speed cpu's.  Since crystalline diamond is the
best thermal conductor/ electrical insulator (OK ultra-wide bandgap semiconduct
or), such a film would be a big help.  also, the drive to low voltage logic (se
e the IEEE spectrum article "High on Low Voltage" recently) will allow faster c
lock speeds at the same power dissapation and also allow smaller transistors.

   So, my question is:   Just because your board manufacturer uses a 2X clock s
cheme and divider to provide the 486 with its 1X clock, why do you insist on th
inking that that clock (oscillator) is directly fed to your chip?  The 486 is a
 1X chip, which is neither an innovation nor a big advance.  It probably has li
ttle or no impact on RF interference and only a slight psychological ecffect on
 the dope at the FCC that licences it (Hey, this is a computer, not an FM trans
mitter!) since many mainframes and workstations have CPU clocks of 100 - 200 MH
z. (covers most of the TV VHF, UHF and cable TV bands, better stop that trend,
too).
    The only technical reason for the 486 being 1X that I can arrive at is that
 a fiberglass, multilevel circuit board is one hell of a capacitive load for a
100 MHz TTL signal to drive.  The vendors knew it and Intel knew it.  So, Intel
 made the 486 a 1X clocked chip so they wouldn't need to use low-dielectric cir
cuit board like teflon at 5X the price.  My only shock at this is that they did
n't rate the previous 2X chips at the input clock rate (Hey, its a 20 MHz 8088!
  Try AMD's 80 MHz 386!   got a 32 MHz 386SX.. Real cheap!) rather than the eff
ective clock rate...

   So, can we end this useless bickering over whether Intel's data book is corr
ect (wrt the input clock speed at least) & get on to the important things in li
fe)