Atari BASIC

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Atari BASIC
AtariBasicExample.png
A program ready to run
FamilyBASIC
Designed byPaul Laughton
Kathleen O'Brien
DeveloperShepardson Microsystems
First appeared1979; 42 years ago (1979)
Stable release
Revision C / 1983; 38 years ago (1983)
PlatformAtari 8-bit family
LicenseCommercial proprietary software
Influenced by
Data General Business Basic[1]
Influenced
BASIC XL, BASIC XE, Turbo-Basic XL

Atari BASIC is an interpreter for the BASIC programming language that shipped with the Atari 8-bit family of 6502-based home computers. Unlike most BASICs of the home computer era, Atari BASIC is not a derivative of Microsoft BASIC and differs in significant ways. It includes keywords for Atari-specific features and lacks support for string arrays, for example.

The language was initially distributed as an 8 KB ROM cartridge. Beginning with the 600XL and 800XL, BASIC is built into the system but can be disabled by holding OPTION while booting. The XEGS disables BASIC if powered without the keyboard attached.

Despite the Atari 8-bit computers running at a higher speed than most of its contemporaries, several technical decisions placed Atari BASIC near the bottom in performance benchmarks. The original authors addressed most of these issues in BASIC XL and BASIC XE. A host of third-party interpreters and compilers like Turbo-Basic XL also appeared.

The complete, annotated source code and design specifications of Atari BASIC were published as The Atari BASIC Source Book in 1983.[2]

History[edit]

The machines that would become the Atari 8-bit family were originally developed as second-generation video game consoles intended to replace the Atari VCS. Ray Kassar, the new president of Atari, decided to challenge Apple Computer by building a home computer instead.[3] This meant the designs needed to include the BASIC programming language, then the standard for home computers.

In early 1978, Atari licensed the source code to the MOS 6502 version of Microsoft BASIC.[4] It was offered in two versions: one using a 32-bit floating point format that was about 7800 bytes when compiled, and another using an extended 40-bit format that was close to 9 kB.[5]

Even the 32-bit version barely fit into the 8 kB size of the machine's ROM cartridge format. Atari also felt that they needed to expand the language to support the hardware features of their computers, similar to what Apple had done with Applesoft BASIC. This increased the size of Atari's version to around 11 kB; AppleSoft BASIC on the Apple II+ was 10,240 bytes long.[a] After six months the code was pared down to almost fit in an 8 kB ROM,[4] but Atari was facing a January 1979 deadline for the Consumer Electronics Show (CES) where the machines would be demonstrated. They decided to ask for help to get a version of BASIC ready in time for the show.[4]

Shepardson Microsystems[edit]

8K Atari BASIC cartridge

In September 1978, Shepardson Microsystems won the bid on completing BASIC[4] and was finishing Cromemco 16K Structured BASIC for the Z80-based Cromemco S-100 bus machines.[6][7] Developers Kathleen O'Brien and Paul Laughton used Data General Basic, an integer-only implementation, as the inspiration for their BASIC, given Laughton's experience with Data General on a time-sharing system.[8]

What became Atari BASIC is a pared-down version of Cromemco BASIC ported to the 6502. That needed 10K of code.[9] To make it fit in Atari's 8K cartridge, some of common routines were moved to the operating system ROMs. This included 1780 bytes for floating point support that were placed in a separate 2K ROM on the motherboard.[4]

Atari accepted the proposal, and when the specifications were finalized in October 1978, Paul Laughton and Kathleen O'Brien began work on the new language.[4] The contract specified the delivery date on or before 6 April 1979 and this also included a File Manager System (later known as DOS 1.0).[9] Atari's plans were to take an early 8K version of Microsoft BASIC to the 1979 CES, then switch to Atari BASIC for production. Development proceeded quickly, helped by a bonus clause in the contract, and Atari took an 8K cartridge version to CES instead of Microsoft's.[10] Atari Microsoft BASIC later became available as a separate product.[11]

Releases[edit]

The version Shepardson gave to Atari for the CES demo was not supposed to be the final version. Between the time they delivered the demo and the final delivery a few weeks later, Shepardson fixed several bugs in the code.[10] Unknown to Shepardson, Atari had already sent the CES version to manufacturing.[12]

This version was later known as Revision A. It contains a major bug in a subroutine that copies memory; deleting lines of code that were exactly 256 bytes long causes a lockup. This was sometimes known as the "two-line lockup" because it did not trigger until the next line of code or command was entered. It cannot be fixed by pressing the Reset key.[13]

Revision B attempted to fix all of the major bugs in Revision A and was released in 1983 as a built-in ROM in the 600XL and 800XL models. While fixing the memory copying bug, the programmer noticed the same pattern of code in the section for inserting lines, and applied the same fix. This instead introduced the original bug into this code. Inserting new lines is much more common than deleting old ones, so the change dramatically increased the number of crashes.[13] Revision B also contains a bug that adds 16 bytes to a program every time it is SAVEd and LOADed, eventually causing the machine to run out of memory for even the smallest programs.[14][15] Mapping the Atari described these as "awesome bugs" and advised Revision B owners "Don't fool around; get the new ROM, which is available on cartridge" from Atari.[15] The book provides a type-in program to patch Revision B to Revision C for those without the cartridge.[16]

Revision C eliminates the memory leaks in Revision B.[15] It is built-in on later versions of the 800XL[14] and all XE models including the XEGS. Revision C was also available as a cartridge.[15]

The version can be determined by typing PRINT PEEK(43234) at the READY prompt. The result is 162 for Revision A, 96 for Revision B, and 234 for Revision C.[17]

Description[edit]

Program editing[edit]

Syntax errors are reported immediately after a line is entered.

Like most home computer BASICs, Atari BASIC is anchored around its line editor. Program lines can be up to three physical screen lines of 40 characters, 120 characters total. The cursor can be moved freely, with the editor automatically tracking which BASIC program line the current screen line is part of. For instance, if the cursor is currently positioned in line 30 and the user uses cursor-up into line 20, any editing from that point will be carried out on line 20.

Atari BASIC's editor catches many errors that would not be noticed in MS-derived versions. If an error is found, the editor re-displays the line, highlighting the text near the error in inverse video. Errors are displayed as numeric codes, with the descriptions printed in the manual.[18] Because of the way the line editor works, the user can immediately fix the error. In the example pictured above (with PRUNT), the error can be fixed by moving the cursor over the U, typing I (the editor only has an overwrite mode), and hitting RETURN.

A line entered with a leading number, from 0 to 32767,[19] is inserted in the current program or replaces an existing line. If there's no line number, the interpreter assigns it the number -1 (800016) and the commands are executed immediately, in "immediate mode". The RUN command executes the stored program from the lowest line number. Atari BASIC allows all commands to be executed in both modes. For example, LIST can be used inside a program, whereas in many interpreters this would be available in immediate mode only.

During entry, keywords can be abbreviated using the pattern set by Palo Alto Tiny BASIC, by typing a period at any point in the word. So L. is expanded to LIST, as is LI.. Only enough letters have to be typed to make the abbreviation unique, so PLOT requires PL. because the single letter P is not unique. To expand an abbreviation, the tokenizer searches through its list of reserved words to find the first that matches the portion supplied. More commonly used commands occur first in the list of reserved words, with REM at the beginning (it can be typed as .). When the program is later LISTed it will always write out the full words with three exceptions: PRINT has a synonym, ?; GOTO has a synonym, GO TO; and LET has a synonym which is the empty string (so 10 LET A = 10 and 10 A = 10 mean the same thing). These are separate tokens, and so will remain as such in the program listing. MS BASICs also allowed ? as a short-form for PRINT, but this used the same token so it expanded back to PRINT when LISTed, treating it as an abbreviation, not a synonym.

The tokenizer[edit]

When the user presses RETURN while editing, the current line is copied into the BASIC Input Line Buffer in memory between 580 and 5FF16.[19] Atari BASIC's tokenizer scans the text, converting each keyword to a single-byte token (for example, PRINT is 2016),[20] each number to a six-byte floating point value, each variable name to an index into a table, and so on, until the line is fully turned into an easy to interpret format. The result is stored in an output buffer located at the first 256 bytes of the lowest available free memory, pointed to by the LOMEM pointer stored at 80, 8116.[19] The output from the tokenizer is then relocated. The program is stored as a parse tree.[b]

Shepardson referred to this complete-tokenizing concept as a "pre-compiling interpreter".[21] The resulting tokenized code eliminates any parsing during runtime, making it run faster. It has the disadvantage that small constants, like 0 or 1, are six bytes each, longer than the original text.

A set of pointers (addresses) indicates various data: variable names are stored in the variable name table (VNTP – 82, 8316) and their values are stored in the variable value table (pointed to at VVTP – 86, 8716). By indirecting the variable names in this way, a reference to a variable needs only one byte to address its entry into the appropriate table. String variables have their own area (pointed to at STARP – 8C, 8D16) as does the runtime stack (pointed to at RUNSTK – 8E, 8F16) used to store the line numbers of looping statements (FOR...NEXT) and subroutines (GOSUB...RETURN). Finally, the end of BASIC memory usage is indicated by an address stored at MEMTOP – 90, 9116) pointer.

Mathematical functions[edit]

Atari BASIC includes three trignometric functions: sine, cosine, and arc tangent. DEG and RAD set whether these functions use radians or degrees, defaulting to radians.

Eight additional functions include rounding, logarithms, and square root. The random function, RND, generates a number between 0 and 1, with the parameter to the function not being used.

String handling[edit]

Atari BASIC differs considerably from Microsoft-style BASICs in the way it handles strings. Microsoft BASIC mostly copied the string-handling system of DEC's BASIC-PLUS, in which strings are first-class types with variable lengths and bounds. This allows both string variables, as well as arrays of strings, as both are represented internally by a computer word pointing to storage on a heap.

In contrast, Atari BASIC copied the string-handling system of Hewlett-Packard BASIC, where the basic data type is a single character, and strings are arrays of characters. A string is represented by a pointer to the first character in the string and its length. To initialize a string, it must be DIMensioned with its maximum length, thereby setting aside the required amount of memory on the heap. For example:

10 DIM A$(20)
20 PRINT "ENTER MESSAGE: ";
30 INPUT A$
40 PRINT A$

In this program, a 20 character string is reserved, and any characters in excess of the string length will be truncated. The maximum possible length of a string in Atari BASIC is 32,768 characters.

MS BASIC includes functions for accessing parts of strings. For instance, LEFT$(A$,10) returns the first 10 characters of A$. These functions create new strings on the heap and return a pointer to the start of the new string. In Atari BASIC the string is represented by an array, and is accessed using array indexing functions, or "slicing". The equivalent statement in Atari BASIC would be A$(1,10); the arrays are 1-indexed, not 0-indexed, so a string of length 10 starts at 1 (not 0) and ends at 10. Because the slicing syntax was the same as the syntax for selecting a string in a two-dimensional array in other BASICs, there was no way to define or work with arrays of strings.

A major advantage of this style of access is that the slicing functions do not create new strings, they simply set pointers to the start and end points within the existing allocated memory. MS BASIC was known for running out of heap space in such programs and entering lengthy garbage collection delays while former temporary strings were removed from memory. Atari BASIC creates new heap entries only with the explicit DIM commands, so memory management is eliminated. This offers a major advantage in terms of performance and memory use in programs with significant amounts of string processing.

Atari BASIC does not initialize array variables, and a string or numeric array will contain whatever data was present in memory when it was allocated. The following trick allows fast string initialization, and it is also useful for clearing large areas of memory of unwanted garbage. Numeric arrays can only be cleared with a FOR...NEXT loop:

10 REM Initialize A$ with 1000 characters of X
20 DIM A$(1000)
30 A$="X":A$(1000)=A$:A$(2)=A$

String concatenation in Atari BASIC works as in the following example. The target string must be large enough to hold the combined string or an error will result:

10 DIM A$(12),B$(6)
20 A$="Hello ":B$="there!"
30 A$(LEN(A$)+1)=B$
40 PRINT A$

The INPUT statement cannot be used with a prompt nor with array variables. The latter must be filled indirectly via a statement like 20 INPUT A:B(1)=A. Array variables in Atari BASIC also may contain two subscripts.

Values in DATA statements are comma-delimited and untyped- consequently strings in DATA statements are not typically enclosed by quote marks in Atari BASIC. As a result, it is not possible for data items to contain a comma but they can incorporate double-quotes. Numeric values in DATA statements will be read as strings or as numeric values according to the type of the variable they are read into. The READ statement cannot be used with array variables.

Arrays have a base index of 0, so a statement such as DIM A(10) actually creates an 11-element array (elements 0-10).

Input/output[edit]

The Atari OS includes a subsystem for peripheral device input/output (I/O) known as CIO (Central Input/Output). Most programs can be written independently of what device they might use, as they all conform to a common interface; this was rare on home computers at the time. New device drivers could be written fairly easily that would automatically be available to Atari BASIC and any other program using the Atari OS, and existing drivers could be supplanted or augmented by new ones. A replacement E:, for example could displace the one in ROM to provide an 80-column display, or to piggyback on it to generate a checksum whenever a line is returned (such as used to verify a type-in program listing).

Atari BASIC supports CIO access with reserved words OPEN #, CLOSE #, PRINT #, INPUT #, GET #, PUT #, NOTE #, POINT # and XIO #. There are routines in the OS for simple graphics drawing functions but not all are available as specific BASIC keywords. PLOT and DRAWTO for line drawing are supported while a command providing area fill for primitive linear geometric shapes is not. The fill feature can be used through the general CIO entry point, which is called using the BASIC command XIO.

The BASIC statement OPEN # prepares a device for I/O access:

10 REM Opens the cassette device on channel 1 for reading in BASIC
20 OPEN #1,4,0,"C:MYPROG.DAT"

Here, OPEN # means "ensure channel 1 is free," call the C: driver to prepare the device (this will set the cassette tape spools onto tension and advance the heads keeping the cassette tape player "paused". The 4 means "read" (other codes are 8 for write and 12 = 8 + 4 for "read-and-write"). The third number is auxiliary information, set to 0 when not needed. The C:MYPROG.DAT is the name of the device and the filename; the filename is ignored for the cassette driver. Physical devices can have numbers (mainly disks, printers and serial devices), so "P1:" might be the plotter and "P2:" the daisy-wheel printer, or "D1:" may be one disk drive and "D2:" and so on. If not present, 1 is assumed.

The LPRINT statement is used to output strings to the printer.

A key can be read by PEEKing memory locations maintained by the keyboard driver or by opening it as a file (e.g. OPEN 1,4,0,"K:":GET #1,A$) although the latter will wait for a keypress.

Typing DOS from BASIC will exit to the Atari DOS command menu. Any unsaved programs will be lost unless a memory-swapping file feature has been enabled on the current disk. There is no command to display a disk directory from within BASIC and this must be done by exiting to DOS.

A typical Atari DOS occupies roughly 5k of memory, thus a cassette-based Atari machine (48k or greater) will have around 37,000 bytes of free BASIC program memory and 32,000 bytes if DOS is present. Atari BASIC cannot use the extra RAM on XL and XE machines.

Graphics and sound support[edit]

Atari BASIC has built-in support of sound, (via the SOUND statement), setting up the screen graphics (GRAPHICS, SETCOLOR, drawing graphics COLOR, PLOT, DRAWTO), joysticks (STICK, STRIG), and paddles (PADDLE, PTRIG). The underlying operating system includes a limited routine to fill simple linear geometric shapes, but Atari BASIC does not have a PAINT/FILL command: this function is called with the XIO command.[22] The SOUND statement allows simple programming of the hardware's 4 independent square-wave channels with parameters for volume, pitch and distortion.

There is no dedicated command for clearing the screen in Atari BASIC, this is usually done with PRINT CHR$(125), which PRINTs the clear screen control code (analogous to PRINT CHR$(147) in Commodore BASIC). Atari BASIC does not include a TAB function; this can be simulated by either POKEing the cursor column position at $55 or the tab position at $C9, which has a default value of 10. The changed values will not take effect until a PRINT statement is executed. There is also no SPC function in Atari BASIC.

Advanced capabilities of the hardware such as higher pitch resolution, high-pass filters, digitised sound and waveforms, player/missile graphics (sprites), redefined character sets, scrolling, and custom graphics modes are not supported by BASIC; these will require machine language routines or PEEK/POKE statements. A few of the 17 basic character/graphics modes supported by the hardware cannot be simply accessed from BASIC on the Atari 400/800 as the OS ROMs do not support them. These include some multicolour character modes (ANTIC modes 4 & 5), descender character mode (ANTIC mode 3) and the highest resolution 2 and 4-color modes (ANTIC modes C & E, 160x192 pixels). The only way to access them is via PEEK/POKE or machine language, setting the ANTIC registers and Display List manually. The OS ROMs on the XL/XE added support for these modes except for ANTIC mode 3, which requires a character set redefined in RAM to operate correctly.[23]

Bitmap modes in BASIC are normally set to have a text window occupying the last four rows at the bottom of the screen so the user may display prompts and enter data in a program. If a 16 is added to the mode number invoked via the GRAPHICS statement, the entire screen will be in bitmap mode (e.g. GRAPHICS 8+16). If bitmap mode in full screen is invoked Atari BASIC will gracefully switch back into text mode when program execution is terminated, avoiding leaving the user with an unresponsive screen that must be escaped by typing a blind command or resetting the computer.

Bitmap coordinates are calculated in the range of 0 to maximum row/column minus one, thus in Mode 6 (160x192), the maximum coordinates for a pixel can be 159 and 191. If Atari BASIC attempts to plot beyond the allowed coordinates for the mode a runtime error occurs.

Advanced techniques[edit]

Line labels[edit]

Atari BASIC allows numeric variables and expressions to be used to supply line numbers to GOTO and GOSUB commands. For instance, a subroutine that clears the screen can be written as GOSUB CLEARSCREEN, which is easier to understand than GOSUB 10000.

Strings as a way to manipulate memory[edit]

The base addresses of a string is stored in a variable table. String addresses can be redirected to point to arbitrary areas of RAM. This allows the rapid memory-shifting routines underlying string and substring assignment can be applied from BASIC to the memory used for the screen or player/missile graphics. This is particularly useful for achieving rapid vertical movement of player/missile images directly from Atari BASIC.

Random access via DATA/RESTORE[edit]

Numeric variables and expressions can be used as the parameter for the RESTORE statement, allowing DATA statements to be randomly accessed through code such as RESTORE ROOMBASE+ROOMNUMBER:READ DESCRIPTION$, TREASURE$, EXITS. This can also be used to emulate static string arrays: RESTORE STRBASE+INDEX:READ A$:PRINT A$.

Error handling with TRAP[edit]

The TRAP statement jumps to a line number when an error occurs, and this reduces the need for manual error-checking. For example, when drawing graphics on the screen it is not necessary to check whether lines go beyond screen boundaries of the current graphics mode. This error state can be trapped, and the error handled if necessary.

Includes[edit]

The ENTER command reads source code from a device and merges it into the current program, as if the user had typed it in. This allows programs to be saved out in sections via LIST, reading them in using ENTER to merge or replace existing code. By using blocks of line numbers that do not overlap, programmers can build libraries of subroutines and merge them into new programs as needed.

Self-modifying code[edit]

The editor can be set-up to repeatedly read input from the screen until an EOF is reached. This allows a program to write new program code followed by a CONT statement to the screen then, positioning the screen cursor at the start of the new code, STOP the running program, causing the new code to be read in then execution be continued by the CONT statement.

Embedded machine language[edit]

Atari BASIC can call machine code subroutines stored in strings or POKEed into memory. The 256 byte area starting at address 153610 (60016) is often used for this purpose.

Machine code is invoked with the USR function. The first parameter is the address of the subroutine and the following values are parameters. If the code is stored in a string named ROUTINE$ it can be called with two parameters as ANSWER=USR(ADR(ROUTINE$),VAR1,VAR2).

Parameters are pushed onto the hardware stack as 16-bit integers in the order specified in the USR call in low byte, high byte order. A final byte is pushed indicating the number of arguments. The machine language code must remove these values before returning via the RTS instruction. A 16-bit value can be returned to BASIC by placing it in addresses 21210 and 21310 (D416 and D516).

Performance[edit]

In theory, Atari BASIC should run faster than contemporary BASICs based on the MS pattern. Because the source code is fully tokenized when it is entered, the entire tokenization and parsing steps are already complete. Even complex mathematical operations are ready-to-run, with any numerical constants already converted to the internal 40-bit format, and variables values are looked up by address rather than having to be searched for.[c] In spite of these theoretical advantages, in practice, Atari BASIC is slower than most other home computer BASICs, often by a large amount.[24]

On two widely used benchmarks of the era, Byte magazine's Sieve of Eratosthenes and the Creative Computing benchmark test written by David H. Ahl, the Atari finished near the end of the list in terms of performance, and was much slower than the contemporary Apple II or Commodore PET,[25] in spite of having the same CPU but running it at roughly twice the speed of either. It finished behind relatively slow machines like the Sinclair ZX81 and even some programmable calculators.[26]

Most of the language's slowness stemmed from three problems.[24]

The first is that the floating-point math routines were poorly optimized. In the Ahl benchmark, a single exponent operation, which internally loops over the slow multiplication function, was responsible for much of the machine's poor showing.[24]

In addition to performing most mathematical operations slowly, the conversion between the internal floating-point format and the 16-bit integers used in certain parts of the language were particularly slow. Internally, these integers were used for line numbers and array indexing, along with a few other tasks, but numbers in the tokenized program were always stored in binary-coded decimal (BCD) format.[27] Whenever one of these is encountered, for instance, in the line number in GOTO 100, the tokenized BCD value has to be converted to an integer, an operation that can take as long as 3500 microseconds.[28] Other BASICs avoided this delay by special-casing the conversion of numbers that could only possibly be integers, like the line number following a GOTO, switching to special ASCII-to-integer code to improve performance.

Another problem is due to how Atari BASIC implemented branches. To perform a branch in a GOTO or GOSUB, the interpreter searches through the entire program for the matching line number it needs.[29] One minor improvement found in most Microsoft-derived BASICs is to compare the target line number to the current line number, and search forward from that point if it is greater, or start from the top if less. This improvement was missing in Atari BASIC.[24]

The most serious problem was the implementation of FOR...NEXT loops. Almost all BASICs, including MS-derived versions, would push a pointer to the location of the FOR on a stack, so when it reached the NEXT it could easily return to the FOR again in a single branch operation. Atari BASIC pushed the line number instead. This meant every time a NEXT was encountered, the system had to search through the entire program to find the corresponding FOR line. As a result, any loops in an Atari BASIC program cause a large loss of performance relative to other BASICs.[24]

Several BASICs for the Atari addressed some or all of these issues, resulting in large performance gains. BASIC XL reduced the time for the Byte benchmark from 194 to 58 seconds,[24] over three times as fast. This was accomplished by caching the location of FOR/NEXT loops, as in other BASICs, and also using this same cache to perform GOTO and GOSUB line lookups. Turbo-Basic XL included a different solution to the line-lookup issue, as well as a re-written, high-performance, floating-point library. On the Ahl benchmark, Atari BASIC required 405 seconds, while exactly the same code in Turbo BASIC took 41.6 seconds, an order of magnitude improvement.[30]

Differences from Microsoft BASIC[edit]

  • The following keywords are not in Atari BASIC: INKEY$, CLS,DEF FN, TAB, ELSE.
  • All arrays must be dimensioned prior to use while Microsoft BASIC defaults an array to 10 elements if not dimensioned.
  • String variables are treated as character arrays and must be dimensioned before use.
  • Atari BASIC does not allow arrays of strings, use LEFT$, MID$ and RIGHT$ to address substrings, or use an operator for string concatenation.
  • There is no support for integer variables.
  • There are no bitwise operators.
  • Variable names can be of arbitrary length and all characters are significant.
  • INPUT cannot include a prompt.
  • PRINT may be abbreviated as ? as in Microsoft BASIC, but Atari BASIC does not tokenize it into PRINT. LIST-ing a program still shows the question mark.
  • The target of GOTO and GOSUB can be a variable or expression.
  • RESTORE may take a numeric constant, variable or expression as a parameter, causing the next READ to begin from the specified line number
  • FOR..NEXT loops in Atari BASIC must have a variable name referenced by the NEXT statement while Microsoft BASIC does not require it.
  • Multiple variables are not permitted with NEXT statements as they are in Microsoft BASIC (e.g., NEXT X,Y).
  • LIST uses a comma to separate a range instead of a minus sign.
  • Syntax is checked and errors highlighted immediately on line entry.

Keywords[edit]

See also[edit]

Notes[edit]

  1. ^ AppleSoft BASIC occupied memory locations $D000 through $F7FF, a total of 10240 bytes.
  2. ^ Although the parse tree is implemented as a set of tables, which is really an implementation detail.
  3. ^ This is the reason MS-BASICs only have two significant letters in variable names, they are stored in a list with only two bytes of ASCII for the name in order to improve searching time.

References[edit]

Citation[edit]

  1. ^ Lorenzo, Mark (2017). Endless Loop: The History of the BASIC Programming Language. Philadelphia: SE Books. p. 106. ISBN 978-1974-27707-0.
  2. ^ Wilkinson, O'Brien & Laughton 1983.
  3. ^ Decuir 2004.
  4. ^ a b c d e f Wilkinson 1982, p. ix.
  5. ^ Steil, Michael (20 October 2008). "Create your own Version of Microsoft BASIC for 6502". Some Assembly Required.
  6. ^ Wilkinson 1982, pp. iv-v.
  7. ^ Cromemco 1978.
  8. ^ Lorenzo, Mark (2017). Endless Loop: The History of the BASIC Programming Language. Philadelphia: SE Books. p. 106. ISBN 978-1974-27707-0.
  9. ^ a b Wilkinson 1982, p. v.
  10. ^ a b Wilkinson 1982, p. x.
  11. ^ Cherry, Charles (June 1987). "BASIC Bonanza". Antic.
  12. ^ Wilkinson 1982, p. vi.
  13. ^ a b "Atari BASIC Bugs". Compute!. July 1986. p. 10.
  14. ^ a b Radcliff, Matthew (September 1995). "Revision C Converter". Antic.
  15. ^ a b c d Chadwick 1985, p. 230.
  16. ^ Chadwick 1985, pp. 250-251.
  17. ^ Hardy, Bob (February 1993). "Keycode Getter". Atari Classics. p. 18.
  18. ^ Manual 1980, Appendix B.
  19. ^ a b c Crawford 1982, p. 10.3.
  20. ^ Crawford 1982, p. 10.6.
  21. ^ Wilkinson, O'Brien & Laughton 1983, p. 5.
  22. ^ Manual 1980, p. 54.
  23. ^ "ATR: chpt.15: Display Lists".
  24. ^ a b c d e f Wilkinson 1985, p. 139.
  25. ^ Ahl, David (November 1983). "Benchmark comparison test". Creative Computing. pp. 259–260.
  26. ^ Ahl, David (January 1984). "Creative Computing Benchmark". Creative Computing. p. 12.
  27. ^ Wilkinson, O'Brien & Laughton 1983, p. 17.
  28. ^ Crawford 1982, p. 8.45.
  29. ^ Winner, Lane (1982). "De Re Atari, Chapter 10: Atari BASIC". Atari, Inc.
  30. ^ "Ahl's Benchmark?". 28 November 2007.

Bibliography[edit]

External links[edit]