Editing Commodore 128 (section)

=== C128 ===
[[file:C128mobo.jpg|thumb|C128 main board]]

In 1984, a year before the release of the Commodore 128, Commodore released the Plus/4. Although targeted at a low-end business market that could not afford the relatively high cost and training requirements of early IBM PC compatibles, it was perceived by the Commodore press as a follow-up to the 64 and would be expected to improve upon that model's capabilities. While the C64's graphics and sound capabilities were generally considered excellent, the response to the Plus/4 was one of disappointment. Upon the Plus/4's introduction, repeated recommendations were made in the Commodore press for a new computer called the "C-128" with increased RAM capacity, an 80-column display as was standard in business computers, a new BASIC programming language that made it easy for programmers to use the computer's graphics and sound without resorting to [[PEEK and POKE]]s, a new disk drive that improved upon the [[Commodore 1541|1541]]'s notoriously slow default transfer rate (without fastloader), as well as total C64 compatibility.<ref>{{cite web|url=http://www.commodore.ca/gallery/magazines/misc/Plus_4_C-16_Disappointing_TPUG_Feb_1985.pdf|title=Plus/4 and C-16: Disappointingly Mediocre}}</ref><ref>{{cite web|url=http://www.atarimagazines.com/creative/v10n12/216_Commodores_port_preview.php|title=Commodore's port; preview of the Plus 4, the Amiga, and Alphacom printers}}</ref>

A new chip, the [[MOS Technology 8563|VDC]], provides the C128 with an 80-column color [[Color Graphics Adapter|CGA]]-compatible display (also called ''RGBI'' for ''red-green-blue plus intensity''). The then-new 8502 microprocessor is completely backward-compatible with the C64's 6510, but can run at double the speed if desired. The C64's Commodore BASIC 2.0 was replaced with BASIC 7.0, which includes [[structured programming]] commands from the Plus/4's BASIC 3.5, as well as keywords designed specifically to take advantage of the machine's capabilities. A [[sprite (computer graphics)|sprite]] editor and [[machine language monitor]] were added. The screen-editor part of the [[KERNAL|Kernal]] was further improved to support an [[insert mode]] and other features accessed through ESC-key combinations, as well as a rudimentary windowing feature, and was relocated to a separate [[read-only memory|ROM]]. The VIC-II chip which controls the 40-column display can only operate at 1&nbsp;MHz, so the 40-column display appears jumbled in <CODE>FAST</CODE> mode. In 80-column mode the editor takes advantage of VDC features to provide blinking and underlined text, activated through [[escape code]]s, in addition to the standard Commodore reverse text.<ref>{{cite web |url=http://www.commodore.ca/manuals/128_system_guide/app-i.htm |title=C128 System Guide{{snd}} Appendix I |publisher=Commodore.ca |access-date=18 April 2012 |archive-url=https://web.archive.org/web/20120531135501/http://www.commodore.ca/manuals/128_system_guide/app-i.htm |archive-date=31 May 2012 |url-status=dead }}</ref> The C128's 80-column mode can display lowercase characters along with [[PETSCII]] graphics characters; 40-column mode is subject to the same "upper- and lowercase" or "uppercase-plus-graphics" restriction as earlier Commodores.<ref>{{harvnb|Waite|Lafore|Volpe|1982}}</ref> The 40- and 80-column modes are independent and both can be active at the same time. A programmer with both a composite and RGB display can use one of the screens as a "scratchpad" or for rudimentary multiple buffer support. The active display can be switched with {{Key press|ESC|X}}.<ref>{{cite magazine|url=https://archive.org/stream/run-magazine-1986-special/Run_Issue_Special_2_1986#page/n69/mode/2up|title=Missing Link Uncovered |pages=66–68 |magazine=[[Run (magazine)|RUN]] | issue=Special Issue 2 |year=1986}}</ref> A hardware reset button was added to the system. The keyboard, however, was not switched to the [[IBM Selectric typewriter|Selectric]] layout as had become standard, instead retaining the same [[ADM-3A]]-derived design as on Commodore's prior models.

[[file:Commodore-128-Computer-BL-Low.jpg|thumb|The back of the Commodore 128]]

NTSC C128s will work with any [[CGA monitor|CGA-type monitor]] ([[Transistor–transistor logic|TTL]] RGB @ 15&nbsp;kHz/60&nbsp;Hz) such as the IBM 5153. However, PAL models of the C128 operate at 50&nbsp;Hz and aren't compatible with most CGA monitors, which expect a 60&nbsp;Hz refresh rate.

Two new disk drives were introduced in conjunction with the C128: the short-lived single-sided [[Commodore 1570|1570]] and the double-sided [[Commodore 1571|1571]]. A dual-disk [[Commodore 1572|1572]] model was announced but never produced. Later on, the 3.5-inch [[Commodore 1581|1581]] was introduced.{{citation needed|date=December 2023}}  The 1581 drive also has more on-board RAM than its predecessors, making it possible to open a larger number of files at one time. BASIC 7.0 includes <code>DLOAD</code> and <code>DSAVE</code> commands to support loading and saving to disk without using the <code>,8</code> or other device number, and also a <code>DIRECTORY</code> command that reads a disk's catalog information directly to screen memory without overwriting BASIC memory as in BASIC 2.0. In addition, the C128 introduces auto-booting of disk software, a feature standard on most personal computers, but absent from Commodore machines up to that point. Users no longer have to type <code>LOAD"*",8,1</code>. BASIC also added a <code>COLLECT</code> command for removing "splat" files (files that were not closed properly and truncated to zero length).{{citation needed|date=December 2023}}

All 1571 drives will normally start up in native mode on the C128. If the user switches to C64 mode by typing <code>GO 64</code>, the drive remains in native mode. But if C64 mode is activated by holding the Commodore key down when powering up, the 1571 then goes into 1541 mode. This routine is necessary for software that performs low-level drive access.{{citation needed|date=December 2023}}

The C128 has twice the RAM of the C64, a far higher proportion of which is available for BASIC programming, due to the new [[Memory management unit|MMU]] bank-switching chip. This allows BASIC program code to be stored separately from variables, greatly enhancing the machine's ability to handle complex programs, speeding [[garbage collection (computer science)|garbage collection]] and easing debugging for the programmer. An executing program can be <CODE>STOP</CODE>ped, its code edited, variable values inspected or altered in [[direct mode]], and program execution resumed with the variable table intact using BASIC's <CODE>GOTO</CODE> command.{{sfn|Simmonds|Borden|1986|p=84}} Although other BASICs support the <code>CONT</code> command to restart execution without clearing variables, editing any code causes them to be cleared.<ref>{{cite web|url=http://www.antonis.de/qbebooks/gwbasman/|title=GW-BASIC User's Guide}}</ref> Different memory configurations can be loaded using BASIC's <code>BANK</code> command.{{citation needed|date=December 2023}}

BASIC 7.0 has a full complement of graphics and sound-handling commands, as well as BASIC 4.0's disk commands and improved garbage cleanup, and support for structured programming via <code>IF...THEN...ELSE, DO...WHILE</code>, and <code>WHILE...WEND</code> loops.{{citation needed|date=December 2023}}

On the downside, BASIC 7.0 ran considerably slower than BASIC 2.0 unless 2&nbsp;MHz mode was used due to its 28&nbsp;KB size (a 250% increase over BASIC 2.0) and having to bank switch to access program variables and BASIC program text (if greater than 16k in length).{{citation needed|date=December 2023}}

The 128's ROM contains an [[List of Easter eggs in Microsoft products|easter egg]]: Entering the command <code>SYS 32800,123,45,6</code> in native mode reveals a screen with a listing of the machine's main developers followed by the message <code>Link arms, don't make them."</code> Also, entering the keywords <code>QUIT</code> or <code>OFF</code> will produce an <code>?UNIMPLEMENTED COMMAND ERROR</code>. These commands are holdovers from the BASIC interpreter intended for a planned but never-produced [[Commodore LCD|LCD portable computer]] and had been intended to exit from the BASIC interpreter and to ignore keyboard input during sensitive program execution, respectively.{{citation needed|date=December 2023}}

The C128's greater hardware capabilities, especially the increased RAM, screen display resolution, and serial bus speed, made it a more capable platform than the C64 for running the [[GEOS (8-bit operating system)|GEOS]] graphical operating system.{{citation needed|date=December 2023}}