Dartmouth BASIC hardware
The terminal, the paper it printed on and the core store behind it, for the two machines that run Dartmouth BASIC.
GE-235
Screen modes
The GE-235 has no video hardware, and neither did anything attached to it. The machine sat in a basement; the user sat at a Teletype Model 33 ASR, a printing terminal on the end of a telephone line, and what it produced was ink on a paper roll. There is one "mode", it is text, and it only ever moves forwards.
The roll is drawn here as a fixed window 72 columns wide — the Model 33's own line — by 24 lines deep. Output scrolls up it, and what leaves the top is gone, exactly as paper rolling past the platen is gone. Nothing can be redrawn: there is no cursor addressing, no clear-screen, no screen memory to write into, and no way to ask where the carriage is. The smallest repaint this machine has is printing the whole picture again.
PRINT lays a line out in five fifteen-column zones, so a comma moves to column 0, 15, 30, 45 or 60; a comma that finds the carriage already inside the fifth zone starts a new line rather than looking for a sixth. A semicolon prints nothing at all — every number already carries two trailing blanks — except past column 66, where it starts a new line to keep the carriage off the margin. The terminal acts on three codes and no others — carriage return, line feed and the bell — while tab and the tape-framing codes pass through unprinted. All of them are listed on the escape codes page.
Colour
The GE-235 has no colour hardware. The output is ink on paper, and the ribbon was black.
Graphics
The GE-235 has no graphics hardware, and Dartmouth BASIC has no graphics keywords: no plotting, no block-graphics characters, no user-definable characters. The printable alphabet is 57 characters — capitals, digits and punctuation — and that is the whole of what can appear on the paper.
A picture is therefore built as characters and printed. The shape that works is to fill a numeric array, then print it a row at a time; because a printed character is taller than it is wide, halve the vertical axis to keep a circle round. Printing a whole picture is slow, and on a shared machine it was slower still — this is where the era's programs earn their reputation for asking a question and then thinking about it for a while.
Sound
The GE-235 has no sound hardware. The only noise in the room came from the teletype: the print head, and the bell code, which struck a physical gong to tell the typist a long run had finished. Nothing is audible here.
Memory
The whole of the machine's core store, region by region. Zoom in to open a band into the parts it groups, and select a region for its addresses and what sits there.
Every address in that map is a word, not a byte. The GE-235's store is twenty bits wide and is addressed a word at a time, three characters to a word and two words to a number. It is one of the two machines here that are not byte-addressed, so a span looks eight times smaller than the equivalent span on any other page and every figure in a region's note is a word count. The viewer's Int / Hex toggle is there for the same reason it is everywhere else, but the machine's own listings are octal throughout and the notes quote them that way.
Only 8,192 words are mapped, which is half the store and the right half. That is what one instruction's address field reaches, and what belongs to the user. The second bank holds whichever language the time-sharing system last read in — BASIC's own compiler is assembled to run there — and a compiled program cannot reach it at all, which is why the run-time subroutines it does need are copied down into the mapped bank before it starts. Everything from word 2,112 upwards is the "6K area", the part written out to disk when the next user's turn comes; below it the executive stays resident.
The user's program sits at the top of that: compiled code grows up from the program area while the source text waits above it to be read, and variables grow down from the top of core to meet it. When they meet, the compilation stops and says the program is too long. Three of the language's limits are the same arithmetic seen from another side — 240 lines, 128 DATA constants and 162 nested GOSUBs are each an allocation in that map divided by what one entry costs.
There are no memory blocks on this machine, and no assembly-language reference to send you to. The GE-235 is offered here as BASIC only: the language has no PEEK, no POKE and no way to call a subroutine that is not a BASIC line, so there is nothing a block of machine code could be loaded for. The cross-dialect Machine code & data blocks overview describes what the machines that do have them do with them.
GE-635
Screen modes
The same terminal, three years later. The GE-635 is a mainframe in a machine room and has no display of its own; what the user sat at was a Teletype Model 33 or 35, printing on a paper roll over a telephone line. There is one "mode", it is text, and it only ever moves forwards.
The line is three columns wider than the GE-235's, which is the manual's own figure rather than a different terminal: the positions on a line are numbered from 0 through 74, and 75 is position 0 of the next line. The roll is drawn here as that 75-column window by 24 lines deep, scrolling up, with nothing that leaves the top recoverable and nothing already printed redrawable.
PRINT lays a line out in the same five fifteen-column zones a comma steps between. A semicolon packs items up instead, each number carrying a leading sign-or-space and one trailing blank, and breaks the line where the next value would have run past column 75 rather than at any fixed column. TAB(n) moves the carriage to a column, and does nothing at all where the carriage is already past it. Either separator at the end of a statement holds the line open for the next PRINT. The terminal acts on the bell, the carriage return and the line feed; end-of-transmission and rub-out pass through unprinted. All five are listed on the escape codes page.
Colour
The GE-635 has no colour hardware. The output is ink on paper, and the ribbon was black.
Graphics
The GE-635 has no graphics hardware, and this BASIC has no graphics keywords: no plotting, no block-graphics characters, no user-definable characters. The printable alphabet runs from the space to code 95 — capitals, digits and punctuation, with the up arrow and the back arrow the ASR-33 prints in the last two slots — and that is the whole of what can appear on the paper.
A picture is therefore built as characters and printed, and this edition makes that noticeably cheaper than its predecessor did: build a row's character codes in a numeric vector, put the length in component 0, and CHANGE it to a string that one PRINT puts on the paper. A repaint that was a loop of PRINTs on the GE-235 is one statement a row here.
Sound
The GE-635 has no sound hardware. The only noise in the room came from the teletype: the print head, and the bell code, which struck a physical gong. There is no statement that sends it, and nothing is audible here.
Memory
The space a program has, region by region. Select the region for its addresses and what sits there.
Every address in that map is a word, not a byte — and a thirty-six-bit word, where the GE-235's is twenty. Four characters of program text pack into one, so the same span looks eight times smaller than the equivalent span on any other page and every figure in a region's note is a word count.
The map has one region where its sibling's has nine, and that is the honest shape of the evidence. The February 1965 compiler listing survives, so the GE-235's map is arithmetic over the listing's own allocation table. Nothing equivalent survives for this machine: the manual states the size of the user's space and nothing at all about where anything sits inside it, so the one span it does give is the one span drawn, and the three claims on it are described rather than partitioned into bands nobody can place.
Those claims are the whole budget, and the manual states them as one rule: let C be the number of characters in the program, M the number of components in all vectors and matrices, and S the number of strings, then C/4 + M + S must be under 8,000. Past that the compiler answers OUT OF ROOM. A separate sentence allows only 100 constants in a program, small integers excepted — which is why nothing here enforces that one, the exemption being unquantified. The terminal's LENGTH command is what reports C.
Nothing is lost by the map's plainness that a program could have observed anyway: this BASIC has no PEEK, no POKE, no USR and no machine code, so there is no address a program can name. There are no memory blocks on this machine and no assembly-language reference to send you to, for the same reason. The cross-dialect Machine code & data blocks overview describes what the machines that do have them do with them.