technical trivia: CPU usage inverse of hard drive usage

[John Doe]

This is confusing and amusing to me. For about 30 seconds, CPU usage
looked like the mirror inverse of hard drive usage in System
Monitor. In other words, when the CPU usage went up, hard drive
usage went down, and vice versa. I doubt it had anything to do with
a unique application.

Newsgroups: alt.binaries.phish
Subject: CPU usage inverse of hard drive usage

In order for my graph to be less cluttered, 0% hard drive usage
starts at the top. When the hard drive is idle, it doesn't hang
around cluttering up the busy area on the bottom of the graph. As
hard drive usage increases, it's pastel blue color indicator moves
downwards from the top.

The CPU usage is purple and shown conventionally, higher means
greater usage.

So the time when the indicators are shown moving together means they
are actually moving in opposite directions.

Seems to get a little weirder.

The fact they are inverse but near perfectly matched on the graph
must be coincidence. I can imagine how they could be inverse, but I
can't imagine how the inverse percentages could cause the two lines
to match up in the same exact location on the graph. In other words,
how come they aren't inverse with one higher than the other, how
come they are in identical inverse percentage locations. Unless
maybe both indicators are moving around the 50% mark for some reason
(the precise percentage is not shown). Hopefully understood, that's
a little difficult to explain.

Have fun.

 

[Nobody]

This is confusing and amusing to me. For about 30 seconds, CPU usage
looked like the mirror inverse of hard drive usage in System
Monitor. In other words, when the CPU usage went up, hard drive
usage went down, and vice versa. I doubt it had anything to do with
a unique application.

The fact they are inverse but near perfectly matched on the graph
must be coincidence. I can imagine how they could be inverse, but I
can't imagine how the inverse percentages could cause the two lines
to match up in the same exact location on the graph. In other words,
how come they aren't inverse with one higher than the other, how
come they are in identical inverse percentage locations. Unless
maybe both indicators are moving around the 50% mark for some reason
(the precise percentage is not shown). Hopefully understood, that's
a little difficult to explain.

If you have a single, single-threaded process taking all of the CPU, then
at any given time the process is either using the CPU or waiting for
something. If the process isn't waiting on network connections, I/O
ports, removable media, etc, then any waiting will be for the hard disk.

When it's waiting, CPU usage will be so low as to be indistinguishable
from zero. If all other processes are essentially idle, then the total CPU
and disk usage will mirror each other (i.e. each will be 100% minus the
other).