Apple II series

The Apple II (stylized as apple ][ and later as apple //) was one of the first highly successful mass produced microcomputer series, manufactured by Apple Computer (now Apple Inc.) and introduced in 1977. It was among the first home computers on the market, and became one of the most recognizable and successful. In terms of ease of use, features and expandability the Apple II was a major technological advancement over its predecessor, the Apple I, a limited production bare circuit board computer for electronics hobbyists which pioneered many features that made the Apple II a commercial success. Introduced at the in 1977, the Apple II was among the first successful personal computers and responsible for launching the Apple company into a successful business (and for allowing several related companies to start at all). Throughout the years, a number of different models were introduced and sold, with the most popular model manufactured having relatively minor changes even into the 1990s. By the end of its production in 1993, somewhere between five and six million Apple II series computers (including approximately 1.25 million Apple II GS models) had been produced.

History
Throughout the late 1980s and much of the 1990s the Apple II was the standard computer in American education. It was popular with business users, families, and schools, particularly after the 1979 release of the popular VisiCalc spreadsheet for Apple II. The original Apple II operating system was only the built-in BASIC interpreter contained in ROM; most commercial Apple II software on disk, e.g. educational games and productivity programs, booted directly on the hardware and either had no operating system or incorporated one of its own (which was usually invisible to the user.) The Apple DOS Disk Operating System was added to support the diskette drive; the last version was "Apple DOS 3.3". Apple DOS was superseded by ProDOS, which supported a hierarchical filesystem and larger storage devices. With an optional third-party Z80 based expansion card the Apple II could boot into the operating system and run, , and other CP/M software. At the height of its evolution, towards the late 1980s, the platform had the graphical look of a hybrid of the Apple II and Macintosh with the introduction of the Apple II GS in 1986. By that point, the platform had 16-bit processing capabilities, a mouse-driven graphical user interface, and graphics and sound capabilities far beyond the original.

The expensive GUI-based Apple Lisa was introduced in 1983, but was not successful commercially. The Macintosh was introduced in 1984, and finally eclipsed the Apple II series in 1993. Even after the introduction of the Macintosh, the Apple II series was Apple's primary revenue source for years: with its associated community of third-party developers and retailers it was once a billion-dollar-a-year industry. The Apple II GS was sold until the end of 1992; the last II-series Apple in production, the IIe, was discontinued on October 15, 1993.

Apple II
The first Apple II computers went on sale on June 5, 1977 with a MOS Technology 6502 microprocessor running at 1 MHz, 4 kB of RAM, an audiocassette interface for loading programs and storing data, and the Integer BASIC programming language built into the ROMs. The video controller displayed 24 lines by 40 columns of monochrome, upper-case-only text on the screen, with NTSC composite video output suitable for display on a TV monitor, or on a regular TV set by way of a separate RF modulator. The original retail price of the computer was US$1298 (with 4 kB of RAM) and US$2638 (with the maximum 48 kB of RAM). To reflect the computer's color graphics capability, the Apple logo on the casing was represented using rainbow stripes, which remained a part of Apple's corporate logo until early 1998. The earliest Apple II's were assembled in Silicon Valley, and later in Texas; printed circuit boards were manufactured in Ireland and Singapore.

An external 5¼-inch floppy disk drive, the Disk II, attached via a controller card that plugged into one of the computer's expansion slots (usually slot 6), was used for data storage and retrieval to replace cassettes. The Disk II interface, created by Steve Wozniak, was regarded as an engineering masterpiece at the time for its economy of electronic components.While other controllers had dozens of chips for synchronizing data I/O with disk rotation, seeking the head to the appropriate track, and encoding the data into magnetic pulses, Wozniak's controller card had few chips; instead, the Apple DOS used software to perform these functions. The Group Code Recording used by the controller was simpler and easier to implement in software than the more common MFM. In the end, the low chip count of the controller contributed to making Apple's Disk II the first affordable floppy drive system for personal computers. As a side effect, Wozniak's scheme made it easy for proprietary software developers to copy-protect the media on which their software shipped by changing the low-level sector format or stepping the drive's head between the tracks; inevitably, other companies eventually sold software to foil this protection. Another Wozniak optimization allowed him to omit Shugart's Track-0 sensor. When the Operating System wants to go to track 0, the controller simply moves forty times toward the next-lower-numbered track, relying on the mechanical stop to prevent it going any further down than track 0. This process, called "recalibration", made a loud buzzing (rapid mechanical chattering) sound that often frightened Apple novices.

The approach taken in the Disk II controller was typical of Wozniak's design sensibility. The Apple II used several engineering shortcuts to save hardware and reduce costs. For example, taking advantage of the way that 6502 instructions only access memory every other clock cycle, the video generation circuitry's memory access on the otherwise unused cycles avoided memory contention issues and also eliminated the need for a separate refresh circuit for the DRAM chips. Rather than using a complex analog-to-digital circuit to read the outputs of the game controller, Wozniak used a simple timer circuit whose period was proportional to the resistance of the game controller, and used a software loop to measure the timer.

The text and graphics screens had a somewhat outdated arrangement (the scanlines were not stored in sequential areas of memory) which was reputedly due to Wozniak's realization that doing it that way would save a chip; it was less expensive to have software calculate or look up the address of the required scanline than to include the extra hardware. Similarly, in the high-resolution graphics mode, color was determined by pixel position and could thus be implemented in software, saving Wozniak the chips needed to convert bit patterns to colors. This also allowed for sub-pixel font rendering since orange and blue pixels appeared half a pixel-width further to the right on the screen than green and purple pixels.

Color on the Apple II series took advantage of a quirk of the NTSC television signal standard, which made color display relatively easy and inexpensive to implement. The original NTSC television signal specification was black-and-white. Color was tacked on later by adding a 3.58 MHz subcarrier signal that was partially ignored by B&W TV sets. Color is encoded based on the phase of this signal in relation to a reference color burst signal. The result is that the position, size, and intensity of a series of pulses define color information.

Apple II plus
The Apple II plus was very similar to the original Apple II. The smaller memory sizes were no longer available, so the II plus always had a total of 48 kB of RAM, expandable to 64 kB by means of the "language card", a 16 kB RAM expansion card that could be installed in the computer's slot 0. The Apple's 6502 microprocessor could support a maximum of 64 kB of memory, and a machine with 48 kB RAM reached this limit because of the additional 12 kB of read-only memory and 4 kB of I/O addresses. For this reason, the extra RAM in the language card was bank-switched over the machine's built-in ROM, allowing code loaded into the additional memory to be used as if it actually were ROM. Users could thus load Integer BASIC into the language card from disk and switch between the Integer and Applesoft dialects of BASIC with DOS 3.3's INT and FP commands just as if they had the BASIC ROM expansion card. The language card was also required to use the UCSD Pascal and FORTRAN 77 compilers, which were released by Apple at about the same time. These ran under a non-DOS operating system called the UCSD P-System, which had its own disk format and included a "virtual machine" that allowed it to run on many different types of hardware. The UCSD P-system had a curious approach to memory management, which became even more curious on the Apple III.

Variants

 * The Apple II Europlus was released in Europe in 1979.
 * The Apple II j-plus was released in Japan in 1979.

Apple IIe
The Apple IIe succeeded the Apple II plus in 1983. The IIe RAM was configured as if it were a 48 kB Apple II plus with a language card; the machine had no slot 0, but instead had an auxiliary slot that for most practical purposes took the place of slot 3, the most commonly used slot for 80-column cards in the II plus.

The auxiliary slot could accept a 1 kB memory card to enable the 80-column display. This card contained only RAM; the hardware and firmware for the 80-column display was built into the Apple IIe, remaining fairly compatible with the older Videx-style cards, even though the low-level details were very different. An "extended 80-column card" with more memory expanded the machine's RAM to 128 kB.

As with the language card, the memory in the 80-column card was bank-switched over the machine's main RAM; this made the memory better suited to data storage than to running software, and in fact the ProDOS operating system, which was introduced with the Apple IIe, would automatically configure this memory as a RAM disk upon booting.

Third-party aux-slot memory cards later allowed expansion up to 1 MB. The 1 K 80-column card also enabled one new graphics mode, Double Lo-Res (80×48 pixels). The extended 80-column card enabled two, Double Lo-Res and Double Hi-Res (560×192 pixels). Both modes doubled the horizontal resolution in comparison to the standard Lo-Res (40×48) and Hi-Res (280×192) Modes; in the case of Double Hi-Res, the number of available colors was increased as well, from 6 to 15. Apple IIe's from the very first production run cannot use Double Hi-Res. Neither of these modes was directly supported by the built-in BASIC, however, so the user had to resort to the use of lots of POKE and CALL commands in BASIC, or assembly language programming, or one of a number of software Toolkits to exploit these modes.

While it was possible for software to switch out the 80-column firmware, making the firmware of a card in slot 3 available with a card in the auxiliary slot, it was not a common thing to do. However, even with the 80-column firmware enabled, slot 3's I/O memory range was still usable, giving it approximately the capability of slot 0 on a II or II plus. This meant that it actually was possible to use slot 3 for things, such as coprocessor cards and language cards, that did not use slot firmware space.

Introduced with the IIe was the DuoDisk, essentially two Disk II 5¼-inch drives in a single enclosure designed to stack between the computer and the monitor, and a new controller card to run it. This controller was (by design) functionally identical to the original Disk II controller but used a different connector, allowing a single cable to control both drives in the DuoDisk. The DuoDisk was plagued by reliability problems, however, and did not catch on as well as the Apple IIe itself.

Apple IIc
Apple released the Apple IIc in April 1984, billing it as a portable Apple II, because it could be easily carried; however, it lacked battery power and a built-in display, so while it was portable, it was not mobile in the common modern sense. The IIc even sported a carrying handle that folded down to prop the machine up into a typing position. It was the first of three Apple II models to be made in the Snow White design language, and the only one that used its unique creamy off-white color. (The other Snow White computers from the Apple II series, the II GS and the Apple IIc plus, were light gray, called "Platinum" by Apple.)

The Apple IIc was the first Apple II to use the updated 65C02 processor, and featured a built-in 5.25-inch floppy drive and 128 kB RAM, with a built-in disk controller that could control external drives, composite video (NTSC or PAL), serial interfaces for modem and printer, and a port usable by either a joystick or mouse. Unlike previous Apple II models, the IIc had no internal expansion slots at all, this being the means by which its compact size was attained. Third parties did eventually figure out how to wedge up to 1 MB of additional memory and a real-time clock into the machine, and a later revision of the motherboard provided an expansion slot that could accept an Apple memory card bearing up to 1 MB of RAM. The disk port, originally intended for a second 5¼-inch floppy drive, eventually was able to interface to 3½-inch disk drives and (via third parties) even hard disks.

To play up the portability, two different monochrome LCD displays were sold for use with the IIc's video expansion port, although both were short-lived due to high cost and poor legibility. (An Apple IIc with the smaller of these displays appeared briefly in the film 2010.) The IIc had an external power supply that converted AC power to 12 V DC, allowing third parties to offer battery packs and automobile power adapters that connected in place of the supplied AC adapter. The Apple IIc (in its American version) was the first microcomputer to include support for the Dvorak Simplified Keyboard, which was activated using a switch above the keyboard. This feature was also later found in late-model American Apple IIe computers (though the switch was inside the computer) and in the Apple II GS (accessible via the built-in control panel). The international models used the same mechanism to switch between the localized and the American keyboard layouts, but did not offer Dvorak.

Apple IIGS
The next member of the line was the Apple II GS  computer, released in September 15, 1986. A radical departure from the existing Apple II line, the II GS featured a true 16-bit microprocessor, the 65C816, operating at 2.8 MHz with 24-bit addressing, allowing expansion up to 8 MB of RAM without the bank-switching hassles of the earlier machines (RAM cards with more than 4 MB were never directly supported by Apple). It introduced two completely new graphic modes sporting higher resolutions and a palette of 4,096 colors; however, only 4 (at 640×200 resolution) or 16 (at 320×200 resolution) colors could be used on a single line at a time, although a technique known as dithering was often employed in software to increase the number of perceived colors.

In a departure from earlier Apple II graphics modes, the new modes laid out the scanlines sequentially in memory. However, programmers in search of a graphics challenge could always turn to 3200-color mode, which involved precisely swapping in a different 16-color palette for each of the screen's 200 scanlines as the monitor's electron beam traced the screen line by line. This exotic technique did not leave many CPU cycles available for other processing, so this "mode" was best suited to displaying static images.

The Apple II GS stood out from any previous (or future) Apple II models, evolving and advancing the platform into the next generation of computing while still maintaining near-complete backward compatibility. The secret of the Apple II GS 's compatibility was a single chip called the Mega II, which contained the functional equivalent of an entire Apple IIe computer (sans processor). This, combined with the flawless 65C02 emulation mode of the 65C816 processor, provided full support for legacy software.

The computer also included a 32-voice Ensoniq 5503, 'wavetable' sample-based music synthesizer chip with 64 kB dedicated RAM, 256 kB of standard RAM, built-in peripheral ports (switchable between IIe-style card slots and IIc-style onboard controllers for disk drives, mouse, RGB video, and serial devices), built-in AppleTalk networking, and a ROM toolbox that supported a graphical user interface derived from the Macintosh toolbox. The computer could run existing 8-bit Apple II software (including software written for the very first Apple II in Integer BASIC), but also supported 16-bit software running under a new OS first called ProDOS 16 and later called GS/OS. The new OS eventually included a Finder that could be used for managing disks and files and opening documents and applications, along with desk accessories — just like the Macintosh. The 16-bit operating system would automatically switch to the text display and downshift to 8-bit mode to run legacy software, while offering a consistent, Macintosh-like graphical interface for native 16-bit applications. Eventually the II GS gained the ability to read and write Macintosh disks and, through third-party software, even multitasking (both cooperative and preemptive, the latter in the form of a Unix-type shell), outline TrueType font support, and in one case, even real-time 3D gaming using texture mapping.

The first 50,000 Apple II GS computers came with Steve Wozniak's "Woz" signature silkscreened on the front and were referred to as the "Woz Limited Edition". These machines are not functionally different from machines from the same time period without the signature.