At 04:35 AM 11/3/2006, Rob Sharp wrote:
On CPU percentage graphs I often see an area shaded in red
underneath the usual green. I think it represents kernel cpu time,
but can someone please tell me what this actually means (if it's the
case...)
Your supposition is correct. From the Process Explorer help file
under System Information:
"Graphs show the CPU usage history of the system as well as the
committed virtual memory usage, and on Windows 2000 or higher systems
an I/O graph shows I/O throughput history. Red in the CPU usage
graph indicates CPU usage in kernel-mode whereas green is the sum of
kernel-mode and user-mode execution."
The "short attention span" explanation of the difference would be
this. Most programs run in user mode. To access components of the
operating system or hardware and memory these programs must send
requests to the operating system via the Win32 API (applications
programming interface). The operating system itself then interacts
with hardware and memory. Programs running in kernel mode bypass
the API and have direct and more or less unfettered access to the
internals of the operating system as well as to memory and
hardware. This allows them to do a lot more, but also increases the
risk if they misbehave. Programs often switch between modes, only
using kernel mode when truly necessary. Device drivers in particular
need to be able to operate in kernel mode. Something like a text
editor will usually find user mode sufficient.
As a short explanation, this is necessarily somewhat oversimplified,
but that's basically it.
James Fadden
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