Virtualise
Appendices
Glossary of Terms
Binary
A two-state system which can be represented by the digits 0 and 1.
Digital computers perform information processing, store data and transmit
information as binary digits.
Bit
Abbreviation for BInary digiT. It is a unit of storage which can takes
the values 0 or 1.
Byte
A group of 8 bits. This is generally the amount of memory required to
store a single character.
Data
Synonymous with information but generally used for the representation
and processing of information by a computer system.
Dynamic area
A dynamic area is a named area of memory created by an
application. The Tasks window obtained by clicking SELECT on the Acorn
icon on the icon-bar lists the dynamic areas at the bottom of the window.
Hexadecimal
Numbers in base 16. The digits are 0123456789ABCDEF, where "A"
to "F" represent the values 10 to 15.
Interrupt
When the control unit stops processing to handle some external
need, such as performing an input/output task.
Logical address
This is the address that the programs running in the
computer use to access memory. The hardware in the computer converts the
logical address into a physical address when required. When virtual
memory is being used the mapping between logical and physical memory is
frequently updated as different areas of memory are accessed.
kB
Abbreviation for kilobyte. This is equivalent to 1024 (2^10) bytes.
MB
Abbreviation for megabyte. This is equivalent to 1,048,576 (1024 * 1024
= 2^20) bytes. This is sometimes used more approximately to refer to 1
million bytes.
Operating system
Essential systems software which coordinates and controls
the use of the system's resources. In the Risc PC this is called RISC OS.
Page fault
An access to a page of memory which is not present at that time
results in an abort on data transfer exception being raised. This is
termed a page fault.
Physical address
This is the address that is actually used to access a
particular section of the memory in the hardware of the computer. A
physical address always references the same part of the same memory chip.
RAM
Random Access Memory. This is the main memory on a chip which allows
data to be stored and modified; read/write memory is a more apt
description.
Virtual memory
This is a system which enables disc space to be used to
simulate extra RAM. It is usually provided as a feature of the operating
system.
VM
Abbreviation for Virtual Memory.
WIMP
Abbreviation for Windows Icons Menus Pointer. This is a generic term
for the graphical interface to the computer. On the RiscPC it is sometimes
called the Desktop.
Version History
1.00 (21-Oct-95)
First official release version.
1.01 (03-Dec-95)
Fixed error handling when out of disc space.
Handling of errors during creation of area handled better.
No longer locks pages used by OS_FSControl 4.
Front-end handles unexpected errors better.
Redraw of page status window speeded up.
Page status display is scalable.
1.02 (08-Jan-96)
Robust handling of flags on entry to file system intercepts.
1.03 (31-Jan-96)
Modified !Run files pass on original parameters.
1.04 (07-Mar-96)
Configuration file moved to
1.05 (10-Apr-96)
Added ability to swap complete tasks to disc.
Changed Yes/No indicators to use ticks.
1.06 (14-May-96)
Fixed handling of dismounts.
1.10 (08-Aug-96)
Made StrongARM compatible.
A dialogue box is used to check deleting a dynamic area.
Added VirtualCheck command to verify module consistency.
Improved handling of OS_Heap operations in virtual memory.
New look title window.
1.11 (12-Sep-96)
Added Virtualise_UserConfigure SWI.
New look configuration window.
Enhanced memory claim options, and new defaults.
Action taken on iconbar icon clicks now configurable.
Option added to purge the swap file directory when loaded.
1.12 (25-Jan-97)
Prevent !Virtualis front-end being swapped out.
System variable size limit only used if none from SWI.
Configuration file correctly terminated with a newline.
Corrected automatic processor recognition.
1.13 (01-Apr-97)
Kludge around bug in revisions less than 3 of SA110.
1.14 (15-Oct-97)
The "keep below" value is used when adjusting the pool size.
Free disk space option is ignored when used with networks.
1.15 (27-May-99)
Fixed the free disk space check with large (>2GB) drives.
Cured spurious crashes when virtual memory pool shrunk.
Fixed rare corruption of the relocatable module area.
Corrected order of loading of Toolbox modules.
More efficient service call handling under Ursula.
Corrected creation of non-empty areas with handlers.
Fixed incorrect stack handling in configuration SWI veneer.
1.16 (23-Aug-99)
Added support for RISC OS 4.
Corrected behaviour if no configuration file found.
Corrected validation of address ranges that wrap.
1.17 (14-Dec-99)
Processor flags preserved across filesystem SWI calls.
Acknowledgments
The author would like to the thank the following people and organisations for their contributions to the development of this application:
- Acorn Computers
The RiscPC, RISC OS and the ObjAsm assembler. - Tim Armes
Hints about how Straylight approached the problems. - Richard Barlow
Patience while an obscure bug was fixed. - Dave Clare
The idea and incentive behind this module. - Aidan Corey
Volunteering to test a potentially dangerous program. - Jonathan Coxhead
For maintaining OSLib even though not at Acorn now. - Robert Davison
The stunning Compo, useful bug reports and comments. - David Jackson
Many bug reports and more ideas for the interface. - Dominic Symes
The brilliant !Zap editor; get a copy immediately. - Robin Watts
!Larger, the greatest backdrop program ever.
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