This is a message that I posted to the United Devices Member Message Board on June 19,.2001, to help another volunteer understand what is meant by CPU cycles.
From: http://forum.ud.com/ubbcgi/ultimatebb.cgi?ubb=get_topic&f=6&t=002630
Wayne Farmer
posted June 19, 2001 18:39
quote:
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Originally posted by Ruthie:
1. How does a CPU 'cycle'?
2. How can these cycles be 'wasted'
(if not running UD, of course!)
3. How are faster CPU's made faster?
4. In our house, we have a 486, a
P75, a Cyrix 166, a P200 and a P800 (I think!). What do these numbers measure?
5. Is there an upper limit to
theoretical CPU speed?
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1.
Think of an orchestra conductor waving his baton. He controls the tempo of
the performance by moving his baton faster or slower. CPUs are 'cycled' by a
'clock' signal whose voltage rapidly goes up and down just like the conductor's
baton. Each up-and-down swing of the clock voltage, from up to down and back up
again, is one cycle.
All the circuits in the CPU follow
that clock signal, which, unlike the conductor's baton, generally stays at the
same tempo all the time. But it's a fast tempo! The latest personal computer
CPUs can receive up to 1,700,000,000 clocks per second; that's 1.7 GHz = 1.7
gigaHertz. My system, a year old, runs at 733,000,000 clocks per second; that's
733 MHz = 733 megaHertz. (Hertz is the standard term for cycles per second;
it's named for a famous scientist named Hertz.)
2.
If the orchestra conductor told all the orchestra to keep silent and
just watch his waving baton for an hour, the orchestra members might well say
that the cycles of the baton were wasted. Similarly, if a CPU is being clocked
but is doing no useful work, then the cycles can be said to be wasted.
3.
Several ways. Here are some:
a. Make the CPU chip smaller, so the
electrons don't have to go so far to get their jobs done (they're limited by
the speed of light). Do this, and you can clock it faster.
b. Design the CPU so that it rarely
has to wait for the things it needs. This lets it keep working all the time,
rather than having to waste clock cycles by waiting for data to come in from
memory, or by having to figure out what its instructions mean before it can do
what they say.
4.
Intel CPUs for personal computers, starting with the IBM PC, have gone
through many generations: 8086 (and its cheaper cousin, the 8088), 80286,
80386, 80486, Pentium, Pentium II, Pentium III, and Pentium 4. (Intel would
have called the Pentium the 80586, but courts ruled that Intel couldn't
trademark the number "80586", so Intel started using the name
"Pentium" instead.) Each generation is more powerful and has more
features than the previous generation.
Your systems are:
an Intel 80486, clocked at probably
no more than 50 MHz;
an Intel Pentium, clocked at 75 MHz;
a Cyrix CPU (a chip made by a
now-defunct Intel competitor, Cyrix; it does the same things as a Pentium, but
is designed differently inside), clocked at 166 MHz;
a Pentium clocked at 200 MHz;
a Pentium III clocked at 800 MHz.
5.
Right now we're limited by how small we can build a CPU (see
"3.a." above). Keeping the CPU from melting is also a problem; the
CMOS transistor technology used in today's CPUs uses electrical power inefficiently,
radiating much of it as heat. The faster you clock a CPU, the hotter the chip
gets. You have to cool the CPU to keep it from melting internally.
For a trove of related information,
see Trish's Hardware Hell (http://www.hardwarehell.com/), and
click on the "CPU and Chipsets" icon. Enjoy!