Hardware Reference
In-Depth Information
the Core is four orders of magnitude more complex than the 8086, so it can do
quite a few things that the 8086 could not do. These piecemeal extensions have re-
sulted in an architecture that is not as elegant as it might have been had someone
given the Pentium 4 architects 42 million transistors and instructions to start all
over again.
It is interesting to note that although Moore's law has long been associated
with the number of bits in a memory, it applies equally well to CPU chips. By
plotting the transistor counts given in Fig. 1-8 against the date of introduction of
each chip on a semilog scale, we see that Moore's law holds here too. This graph
is given in Fig. 1-13.
Core i7
10G
Core 2
Core Duo
1G
Pentium 4
Pentium III
100M
Pentium II
10M
Pentium
Moore's law
1M
80286
80486
Pentium
Pro
100K
80386
8086
8080
10K
8008
4004
1K
8008
100
10
1
1970
1975
1980
1985
1990
1995
2000
2005
2010
Year of introduction
Figure 1-13.
Moore's law for (Intel) CPU chips.
While Moore's law will probably continue to hold for some years to come, an-
other problem is starting to overshadow it: heat dissipation. Smaller transistors
make it possible to run at higher clock frequencies, which requires using a higher
voltage. Power consumed and heat dissipated is proportional to the square of the
voltage, so going faster means having more heat to get rid of. At 3.6 GHz, the
Pentium 4 consumes 115 watts of power. That means it gets about as hot as a
100-watt light bulb. Speeding up the clock makes the problem worse.
In November 2004, Intel canceled the 4-GHz Pentium 4 due to problems dissi-
pating the heat. Large fans can help but the noise they make is not popular with
users, and water cooling, while used on large mainframes, is not an option for
desktop machines (and even less so for notebook computers). As a consequence,
the once-relentless march of the clock may have ended, at least until Intel's engin-
eers figure out an efficient way to get rid of all the heat generated. Instead, Intel
CPU designs now put two or more CPUs on a single chip, along with large shared
