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Virtualise

The desktop front end

Introduction

This chapter is intended as a reference to all of the features included in the "!Virtualis" front-end. For a simple introduction read the "Tutorial" file.

The front-end supports interactive help; use Acorn's !Help application to obtain information about the item under the mouse pointer.

Starting the Program

It is necessary to register the software before using it for the first time.

See the "Tutorial" chapter for details of how to do this.

Start the front-end by simply double-clicking SELECT on the "!Virtualis" icon in a directory viewer. After a short delay the application icon will appear on the icon-bar.

The Icon Bar

Clicking MENU on the icon which appears on the iconbar opens the main program menu which offers the following options:

• Info
  Moving over the sub-menu arrow displays a standard program information window. The version number should be the same as the version of the Virtualise module being used.
• List areas...
  This opens up a window giving details of all the dynamic areas in the machine, and allow various operations to be performed.
• Page faults...
  This opens up a window showing the number of page faults which have been serviced classified according to the type of instruction which generated the exception.
• Configure...
  This opens up a dialogue box which allows the Virtualise module to be configured.
• Automatic...
  This opens up a window listing the dynamic area names for which virtual memory will automatically be enabled when they are next created.
• Tasks...
  This opens up a window listing the current WIMP tasks, allowing specified tasks to be suspended and swapped to disc.
• Quit
  Quits the front-end program. The module is not affected.

These options can be assigned to SELECT and ADJUST clicks on the iconbar icon.

Dynamic Area List Window

The dynamic area list window can be opened by either selecting the "List areas..." option from the icon-bar menu.

The window which is opened displays details of all the dynamic areas which exist in the computer. This list is updated once per second on WIMP null-polls. Areas with numbers under 256 (those which are not listed as dynamic areas in the Taskmanager) are shaded. The columns of details are:

• Name
  The name of the dynamic area as displayed by the TaskManager or returned by OS_DynamicArea 2.
• Number
  The dynamic area number as used with OS_DynamicArea, OS_ReadDynamicArea and OS_ChangeDynamicArea.
• Maximum
  The maximum size (reserved logical address space) of the dynamic area.
• Logical
  The current logical size of the area, i.e. how much memory the user of the area thinks is being used.
• Physical
  The current physical size of the area, i.e. how much real memory is being used to support accesses to area. If the area has not got virtual memory enabled then it will be the same as the logical size.
• VM
  An indicator of whether virtual memory is enabled for the area.

Unshaded areas may be selected by clicking with SELECT and ADJUST in the usual manner. Clicking Menu opens a menu that allows various operations to be performed. The options offered are:

• Virtualise
  Either enable or disable virtual memory for all of the selected dynamic areas. If any of the selected areas have virtual memory already enabled then a tick appears next to this item. This option is shaded if no areas are selected.
• Delete area...
  Remove the selected dynamic areas. This option is shaded if no areas are selected. A dialogue box is opened to confirm the deletion.
• Show map...
  This opens a window for each selecting area showing the status of all the pages of memory within the areas.

Double-clicking SELECT on a dynamic area entry has the same effect.

• Select all
  This selects all of the dynamic areas.

• Clear selection
  This deselects any areas which are selected.

The Virtualise and Remove options should obviously be used with care; it is very easy to crash the computer if these are used carelessly.

If an application is dragged into the list window the "Modify application" dialogue box is opened. This is described in the next section.

Modify Application Dialogue

This allows the application to be modified so that it always uses virtual memory when it is run. A backup of the application should be made before using this option.

The top of the window shows which application will be altered. The centre of the window controls the operation to perform:

Enable virtual memory by default

This option modifies the !Run file of the application to automatically enable virtual memory for the dynamic areas which are selected within the dynamic area list window.

These should be the dynamic areas that are used by the application being modified. This will take effect the next time that the application is started. This option also copies the Virtualise module into the "!Boot.Choices.Boot.PreDesk" directory to ensure that it is always loaded.

Size limit - This is the maximum size that will be set for the selected dynamic areas.

Restore original !Run file

This attempts to restore the application to the state it was in before it was modified. Due to the way in which this operates it may not take effect until the next time the computer is reset.

Uninstall module

Selecting this option removes the Virtualise module from the boot sequence if it was previously installed by the enable virtual memory option.

At the bottom of the window are two action buttons:

• Cancel
  Clicking on this icon aborts the modification, leaving the application unchanged. Pressing Escape has the same effect.
• OK
  Clicking on this icon performs the selected modification.

It is also possible to press Return to have the same effect.

Page Status Window

Any number of page status windows may be opened. The main part of the window at the top contains a square for each page of memory within the dynamic area.

The colour of the square indicates the state of that page. Clicking MENU within the window opens a menu:

• Key...
  A window showing the meaning of the different colours.
• Zoom
  A list of the possible scales at which the status display can be shown.

The lower part of the window has an Update button which takes a new snapshot of the state of the dynamic area. Also shown is the dynamic area number and name.

Note that the access count is only meaningful if the NFU page replacement policy is configured.

Configuration Window

The configuration window is split into two areas. The scrollable area on the left displays all of the options that may be controlled. The area on the right contains three buttons:

• Save
  Save the values shown. These values will be used by both the Virtualise module and the "!Virtualis" front-end each time they are started in the future.
• Read current
  Reads the current settings from the Virtualise module.

The numerical values are rounded down to 0.1MB multiples before being displayed.

• Set new
  Sets the values shown in the window. The settings are then read back and window updated.

If the Virtualise module is not loaded the last two buttons will produce an error message.

The section of the scrollable area entitled "Memory usage" shows each of the values which can be set using Virtualise_Configure, and one extra that can be set using Virtualise_UserConfigure. Note that these values can only be specified to the nearest 0.1MB due to the way in which the Toolbox system handles number range gadgets. The items are:

• Claim up to
  The amount of real memory to claim automatically for the virtual memory pool if it could be useful.
• Keep below
  The amount of real memory to keep even if other applications require more memory than is available.
• Leave free
  The minimum amount of memory to leave free when the size of the virtual memory pool is adjusted.
• Size limit
  The amount of logical address space reserved for dynamic areas if -1 is specified as the maximum size when they are created.

The second section of the scrollable area entitled "Disc usage" controls the usage of disc space for swap files. The current version only has a single item:

• Leave free
  The amount of disc space to leave free when a swap file is either created or enlarged. This values may sometimes be exceeded due to the way in which disc space is allocated.

The next section of the scrollable area entitled "Swap file directory" allows the directory used for storing swap files to be set. This sets the system variable Virtualise$SwapDir as a macro, so system variables (such as <Wimp$ScrapDir>) may be included. There are three ways of setting the directory: dragging the directory icon to a directory window, dragging a file or directory icon into the configuration window, or by typing the required pathname into the writable icon. Note that a change to the swap file directory only affects swap files created after the change has been made;

Existing swap files are not moved.

This section of the window also contains an option button. If the option is selected then the swap file directory will be purged each time the Virtualise module is loaded. This will delete any swap files that have been left from previous uses, and can prevent the disc being filled with unused files.

The next section of the scrollable area entitled "Page replacement policy" sets the algorithm used to select pages to swap to disc. The current options are:

• NFU Not frequently used.
  This chooses the page that has been accessed the least frequently.
• FIFOFirst-in, first-out.
  Pages are swapped out in the order they were originally swapped in. In other words this chooses the oldest page.
• Random
  A page is chosen at random, irrespective of how recently or frequently it has been used.

There are also two option buttons which control whether pages are read and written individually or grouped into larger file operations (which should be faster).

The next section of the scrollable area entitled "Load module" controls whether the Virtualise module is loaded within the !Boot sequence. The options are:

In !Boot sequence

When this option is selected, the Virtualise module will be placed into the "!Boot.Choices.Boot.PreDesk" directory to ensure that it is always loaded.

When !Virtualis is run

When this option is selected, any copy of Virtualise in the "!Boot.Choices.Boot.PreDesk" directory will be deleted. The module will then only be loaded when the !Virtualis front-end is run.

The final section of the scrollable area entitled "Iconbar clicks" allows actions to be assigned to SELECT and ADJUST clicks on the iconbar icon. The options are the same as those available from the iconbar icon menu.

Page Faults Window

The "Number of page faults" window is opened by selecting the "Page faults..." option from the icon-bar menu. The window displays the numbers of virtual memory page faults which were generated by different classes of instruction since the module was loaded.

Note that page faults generated by floating point processor instructions will only be listed under "Coprocessor data transfer" if a real floating point unit is being used. If Acorn's Floating Point Emulator is being used then it will be an instruction within the emulator code which actually generates the exception.

Automatic Virtual Memory Window

The automatic virtual memory list window is opened by selecting the "Automatic..." option from the icon-bar menu.

The window which is opened lists the names of the dynamic areas for which virtual memory will be enabled by default. This operates by setting system variables as described in the "Module" file. This list is updated once per second on WIMP null-polls. The columns of details are:

• Name
  The name of the dynamic area as displayed by the TaskManager or returned by OS_DynamicArea 2. If a system variable corresponding to an unknown dynamic area then the capitalisation and special characters may not be exactly the same as the actual dynamic area name.
• Size limit
  The maximum size (reserved logical address space) that should be allocated for the dynamic area if no limit is specified by the program that creates it.

Dynamic area names may be selected by clicking with SELECT and ADJUST in the usual manner. Clicking Menu opens a menu that allows various operations to be performed. The options offered are:

Size limit

• Add area
  The sub-menu lists all the names of dynamic areas that have been seen by the "!Virtualis" front-end. Select the name of a dynamic area to add it to the list. It is initially added with a size limit of 256MB. The list of known dynamic areas is saved between sessions.
• Remove area
  Remove the selected dynamic area names from the list. This also unsets the corresponding system variables.
• Save
  Save a list of the current settings. This option also copies the Virtualise module into the "!Boot.Choices.Boot.PreDesk" directory to ensure that it is always loaded. The file of dynamic areas is read by the Virtualise module each time it is loaded. Hence once the use of virtual memory has been configured, it is not necessary to use the "!Virtualis" front-end.
• Select all
  This selects all of the dynamic areas.
• Clear selection
  This deselects any areas which are selected.

Task Swapper Window

The task swapper window is opened by selecting the "Tasks..." option from the icon-bar menu.

The window which is opened lists the names of the WIMP tasks running within the computer. The columns of details are:

• Task
  The name of the task, as displayed in the TaskManager window.
• Size
  The size of the task, either in memory or on disc. For active tasks this is the same as the figure displayed by the TaskManager.
• Disc
  An indicator of whether the task has been swapped to disc.

Clicking on a task within the window attempts to suspend the task, and swap it to disc. Clicking on a suspended task attempts to reload it and resume execution. If ADJUST is used, instead of SELECT, then the window is also closed.

When a task is suspended, any open windows belonging to the task are closed, and any icons on the icon-bar are replaced. The task may be resumed by clicking on any of the replacement icon-bar icons.

If it is not possible to restore a task, for example if there is insufficient memory, then an error is displayed. This offers the following options:

• Cancel
  Close the error window, and leave the task suspended.
• Kill Task
  Stop the task immediately. This does not exit the task normally, so should only be used as a last resort.

If an attempt is made to exit the desktop while a task is swapped out, an error dialogue is displayed, and the following options are offered:

• Restore
  Attempt to swap the task back. The shutdown is aborted.
• Abort
  Abandon the shutdown, and leave the task suspended.
• Shutdown
  Kill the task, and resume the shutdown. The task is not exited normally, so this should only be used as a last resort.

Not all tasks can be safely swapped out - if in doubt, save any important data (in all applications) before trying to suspend the task. Programs with filters applied are likely to cause problems.

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