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Welcome to my personal home page. There are many pages on this site concerning various topics of an entertaining, yet somewhat technical, nature that many visitors should find fascinating.


At long last, an update to my cryptography pages!

A description of the Abwehr SG-39, which was similar to an Enigma, but with a pinwheel assembly controlling the rotor stepping, has been added to the page on relatives of the Enigma, and a description of the SG-41 has been added to the page on Hagelin machines.

The page on color filter array designs has been updated to include a reference to the Hubble palette. A recent previous update described the new X-Trans and EXR designs from Fujifilm.

The rules for Hiashatar, the current Mongolian form of Great Chess, have been revised so that there is enough detail to actually attempt to play a game of it.

The section at the end of the page in my description of an imaginary computer architecture that describes Subdivided Medium floating-point operation has received a substantive change which modifies how this form of addressing operands of unusual length works.

A page in the section on the slide rule has been updated with a brief description of the Hemmi 200 and 201 slide rules, with extra-long split scales to allow more accurate multiplication. The Unique Ten-Twenty is also mentioned. Also, the discussion of a complex number cylindrical slide rule has been expanded, with a mention of the Faber-Castell 989 Complex Slide Rule Calculator.

The page on Dice of Other Shapes (than cubical) has been updated to include an idea of mine for using the idea behind Koplow Double Dice to make a heterogenous die of that type - a d20 inside a transparent d6 - to make a universal die. As well, some information on the history of polyhedral dice has been updated, and more information on the current availability of some new unusual types of dice has been added.

The page on computer arithmetic, as it contained a list of alternate versions of hexadecimal notation used on early computers, now has had duodecimal characters, and some early character sets with characters for pence in sterling currency, added; one of those character sets, used on the Elliott 503 computers, is Cluff-Foster-Idelson code, which anticipated ASCII. On both that page, and the page about punched card codes, I've also added a reference to the GOST 10859 code from the former Soviet Union.

The former of those two pages now also exhibits the character coding for the STRETCH (IBM 7030) computer, as that code, like GOST 10859, has many of the special characters originally used for ALGOL. The IBM 7030 code had the unusual characteristic of putting the upper-case and lower-case letters of the alphabet in the sequence aAbBcC... in the vain hope of simplifying collation; and so I've also included in the diagram for it an image of the ARMSCII code, which placed the letters of the Armenian alphabet in AaBbCc... style order.

As well, I've made some changes to the diagrams on this page, about modifying ASCII, and a diagram of FIELDATA has finally been added to this page.

An attempt has been made to unravel the mystery of the tone generator used for the chorus feature of the model BC, D, and E Hammond organs on this page. RECENTLY UPDATED, thanks to my having been able to see a photo of part of a chorus tone generator.

The page about building blocks and the Pythagorean triangle has been updated showing two ways in which additional directions of walls could be added with alternate block types.

Several updates have recently been made to the section on Chess, among them:

A page describes a number of the systems for recording the moves of a Chess game, including several quite obscure ones.

The description of Korean Chess has been corrected and extended.

Most recently, yet another variant form of Chess has been added, placing the King and Queen off center to better preserve Castling on an enlarged board, and proposing an interesting use for a second King.

A new page has been added discussing memory interleaving techniques.

The apparently contradictory conditions for the efficient use of data elements the lengths of which are not in a simple power-of-two relationship have now been reconciled. On this page I explain how, after dividing a 256-bit memory word into five or seven parts (for 51-bit intermediate-precision and 36-bit single-precision floating-point numbers), I can then, at the cost of a small amount of additional wastage of storage space, calculate physical addresses efficiently without resorting to division by five or seven.

As well, several portions of the section on A Computer Architecture have been modified, both to incorporate this added feature, and to incorporate the feature of selectively saving or updating condition codes to allow speculative execution to be avoided.

Also, a 12-bit oriented example architecture, fleshed out in more detail than the previous 12-bit example in that section, has been added to the section on dealing with nonstandard lengths of data.

The section on basic HTML has been extended with a page about the use of Cascading Style Sheets for formatting.

Two early computers from the People's Republic of China are now mentioned on this site: a description of the instruction format of the 757 vector computer has been added to the section on 32-bit computers, and a description of the instruction format of the DJS-21 computer has been added to the next page.

The section describing the Fast Long Single and Fast Intermediate modes of operation has been moved to its own page, and has been revised and extended.

Cryptography Entry Page
Index Page

Pencil and Paper SystemsElectrical and Mechanical Cipher MachinesTelecipher MachinesThe Computer EraPublic-Key CryptographyMiscellaneous Topics

Map Projections Entry/Index Page

Cylindrical ProjectionsAzimuthal ProjectionsConic ProjectionsPseudocylindrical and Pseudoconic ProjectionsPolyconic ProjectionsConventional ProjectionsOther Conformal ProjectionsOther Equal-Area ProjectionsMiscellaneous Projections

A brief page with a few annotations about the Girl Genius web comic, for which a link banner appears to the right, is now on this site.


Featured Images

Signal Flag Systems
The Vocalization of Hebrew
Introduction to HTML
Color Charts
Building Blocks and the Pythagorean Triangle
Efficient and Flexible Text Encoding
Design for a Tall Building

Movie and TV Aspect Ratios
A Limitation of Color Photography
Color Filter Array Designs

Don't Touch That Dial!
Color Television Madness
Four Speakers from Two Channels?
A Problem in Applied Geometry

Chinese Character Encodings

A Phonemic Alphabet
Two Schemes For Elections
Patterns in Nature and Myth

A Note on Large Numbers
A Unified Architecture for Telephone Numbers
On Philosophy and Ethics


How Does A Computer Work?What Computers Are Made FromComputer ArithmeticThe General Layout of a ComputerThe Subroutine CallThe Old Days: Computing Without RAMThe Old Days: Decimal ComputersThe Perfect Computer?Minimizing ChangeNot Quite RISCA Historical View of FORTRANRemembering APLComputer Architectural PreferencesComputer Front PanelsThe Punched CardPrint Train TriviaPrinting Terminals and Proportional SpacingDigital Magnetic Tape RecordingReforming ASCII and Unicode

Keyboards Entry/Index Page

Large KeyboardsKeyboards for Genuinely Large Character SetsComments on the Keyboard of the IBM PCKeyboard ArrangementsThe Keyboard Overlay ProblemMaking Keyboards More CompactAn Attempt at a Popular KeyboardScan Codes Demystified


The Slide RuleInfinityArchimedean SolidsThe Fourth DimensionRotations of a DodecahedronExamples of GroupsTwo Famous EquationsEuler's ConstantSphere PackingsGödel's Theorem and the Halting ProblemMagic SquaresThe Mandelbrot FunctionDiophantus at the Printer's ShopChange Ringing

Tilings Entry/Index Page

The 17 Wallpaper GroupsPentagonal TilingsOctagonal TilingsDodecagonal TilingsHeptagonal Tilings

Chess Entry/Index Page

A Few OpeningsChess NotationThe Immortal Game (Anderssen-Kieseritzky)The Immortal 50th Game (La Bourdonnais-MacDonnell)

Comments on the RulesThe Crisis in ChessDynamic ScoringA Proposed Rating SystemTournament Tiebreaking

Well-Known Forms of ChessTraditional Enlarged Forms of ChessWarring States ChessThe Game of the Three KingdomsJetan, Barsoom's Game of ChessThe Game of BattleChess-DraughtsHexagonal ChessHexagonal Chess, Part 2S. Waider's Chess for Three PlayersEnlarged and Improved ChessFour-Player Chess

Leaping Bat ChessRandom Variant ChessChess 2016Corrected Random Variant ChessThree-Dimensional ChessEngagement ChessFive-Player ChessAn Unusual Board for Three-Player ChessSpectral Realm ChessHalf-Shogi ChessTemporary Marsellais ChessAntimatter Universe ChessAn Ordinary VariantAntimatter Universe Flag ChessYet Another Ordinary VariantRotating Spaceship ChessA Problem CorrectedPrequel ChessReformed ShatranjTwo Off-Centre Ordinary VariantsSnake Chess

Checkers Entry/Index Page

Two-Move and Three-Move RestrictionsThe Perfect Game [of checkers]?Other Forms of CheckersHasami Shogi, Seega, and Other Related GamesLudus LatrunculorumEnglish Gothic Double Checkers

Board Games

Board Games Other Than ChessA Few Board Games of InterestComments on Wei Ch'i (or Go, or Baduk)Other Uses for a Go BoardThe Greatest Modern Board Game of SkillBackgammonThe Jungle GameRithmomachyThe Perfect [board] Game?Making Wargames More ComplicatedMaking Full Use of Three Ordinary DiceThe World is RoundMaking Board Games More ComplicatedSpace Battles in Three DimensionsThe Real Game of BridgeSiberian Semi-Contract Whist (or Bridge)Bridge for Six: Trivial WhistCounting Tricks Before They're HatchedThe Semi-Tarock Deck

Science Entry/Index Page

A Few Words About StarsA Space Habitat DesignTravel to MarsLining up the PlanetsThe Equation of TimeThe Inconstant MoonThe Einstein-Podolsky-Rosen experimentsThe Fine-Structure ConstantPunctuated Equilibria

Telescopes Entry/Index Page

How a Telescope WorksKinds of TelescopesTelescope MountingsEyepiecesIntroduction to Geometrical Optics

Calendars Entry/Index Page

Perpetual CalendarsA Luni-Solar CalendarA Simplified Calendar ProposalJulian Day NumbersA Martian CalendarA Modest Proposal for the Abolition of the Leap SecondHappy Easter!Happy Hanukkah!The Mayan Calendar

Unit Conversions Unit Conversions

Printer's UnitsTemperature ScalesFrom Gold Coins to Cadmium LightGauge is Not ScaleThe Size of the Piano KeyboardSome Unusual Units of LengthOld Feet and Old PoundsAvoiding the Metric System


The Musical ScaleMore Complicated TemperamentsA Bit About Musical NotationSome Interesting KeyboardsA Bit About ChordsApproximating Equal TemperamentThe Hammond OrganA Minor Mystery: The Chorus Tone Generator

A Computer Architecture
A Computer Architecture
Entry/Index Page

Memory-Reference InstructionsAdditional InstructionsBasic ArchitectureTagged Operation ModesRestricted FunctionalityOff-Chip Processing

A Computer Language
A Computer Language
Preview Page

Basic InformationWriting an EXALT ProgramArithmetic StatementsControl StructuresType DeclarationStorage ClassesSubprogramsParallel ProcessingUser-Defined TypesProgram Source ModificationExpression EvaluationInput/OutputDatabase ManagementException HandlingAdvanced FeaturesAppendix II: Implementation Notes

Contact Information and Notes

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Copyright (c) 2000, 2001, 2002, 2004, 2005, 2008, 2010, 2011, 2012 John J. G. Savard