The XCenter "Sentinel" widget shows you a graph of the current memory consumption on your system.

The sentinel takes a bit of getting used to, but it comes in quite handy after a while. Not unlike the "Pulse" widget, it shows you a graph of how memory usage has evolved on your system over time. This graph is updated every two seconds.

However, the sentinel shows you several graphs at the same time, in different colors, with the current measurements (in MB) painted in the same colors on the left:

The graphs represent the following:

  1. The top value (in green) is the currently free physical RAM. This is the same value as with the "Memory" widget. So if you have 128 MB of RAM on your system, this will never go above that value (and most likely never reach it, of course).

  2. The middle value (in blue) is the currently used physical RAM. If you add this value to the top value, you should get your total RAM. (Yes, this should be 128 MB on my system, but obviously I got rounding errors here.)

  3. The bottom value (in purple) is the current size of your swap file. Add this number to the top two values, and you get the current amount of virtual memory on your system.

    As you can imagine, this sum (the total virtual memory) can vary over time, as you can see in the above screenshot. On the left, you can see that for some reason the swap file grew really big, which made the virtual memory grow. OS/2 then later chose to shrink the swap file again.

  4. If you have a recent win32k.sys driver from Odin (March 2001 or newer) installed, you will also get a fourth red graph even below the purple graph which shows you the free space inside the swap file.
Now, the gray area above the colored graphs really has no meaning. It is only the result of the scaling that the sentinel performs on the display. When time passes, you will see that as soon as the "bump" on the left leaves the screen, the display is rescaled and the gray area is then used for the display as well.

Here is another screenshot which shows you the memory consumption while &xwp; was recompiled on my system:

Since I heavily use a RAM disk for precompiled header files, it is quite obvious that the free RAM becomes used up during the compile process.

The sentinel widget accepts colors and fonts that are dropped on it. Presently, you can only change the background color though. Besides, it is sizeable.

Implementation Details

The source of the information that is displayed by the sentinel widget depends on whether a recent version of Odin's win32k.sys driver is installed.