The Apple II (stylized as ) is a personal computer released by Apple Inc. in June 1977. It was one of the first successful mass-produced microcomputers and is widely regarded as one of the most important personal computers of all time due to its role in popularizing home computing and influencing later software development.
The Apple II's initial electrical design was done by Steve Wozniak. The system is based around the MOS Technology 6502, an 8-bit microprocessor. Howard Cantin designed the printed circuit board, Jerry Manock designed the foam-molded plastic case, and Rod Holt developed the switching power supply. Steve Jobs was not involved in the electrical design of the Apple II, but contributed in its high-level design and positioning as a non-hobbyist general purpose appliance.
The Apple II was introduced by Jobs and Wozniak at the 1977 West Coast Computer Faire, and marks Apple's first launch of a computer aimed at a consumer market—branded toward American households rather than businessmen or computer hobbyists. Byte magazine referred to the Apple II, Commodore PET 2001, and TRS-80 as the "1977 Trinity". As the Apple II had the defining feature of being able to display color graphics, Apple's company logo was redesigned to have a spectrum of colors.
The Apple II was the first in a series of computers referred to by the Apple II name. It was followed by the Apple II+, Apple IIe, Apple IIc, Apple IIc Plus, and the 16-bit Apple IIGS—all of which remained compatible. Production of the last available model, the Apple IIe, ceased in November 1993.
History The Apple II was intended to be a successor to the Apple I. Steve Wozniak designed the Apple II circuit to have better capabilities than the Apple I, including color display. It was designed with an MOS Technology 6502 microprocessor running at 1.023 MHz ( of the NTSC color subcarrier). The video controller displays 24 lines by 40 columns of monochrome, uppercase-only text on the screen (the original character set matches ASCII characters 20h to 5Fh), with NTSC composite video output suitable for display on a video monitor or on a regular TV set (by way of a separate RF modulator).
Certain aspects of the system's design were influenced by Atari, Inc.'s arcade video game Breakout (1976), which was designed by Wozniak, who said: "A lot of features of the Apple II went in because I had designed Breakout for Atari. I had designed it in hardware. I wanted to write it in software now".Connick, Jack: "...And Then There Was Apple". Call-A.P.P.L.E. Oct 1986: 24. This included his design of color graphics circuitry, the addition of game paddle support and sound, and graphics commands in Integer BASIC, with which he wrote Brick Out, a software clone of Breakout. Wozniak said in 1984: "Basically, all the game features were put in just so I could show off the game I was familiar with—Breakout—at the Homebrew Computer Club. It was the most satisfying day of my life [when] I demonstrated Breakout—totally written in BASIC. It seemed like a huge step to me. After designing hardware arcade games, I knew that being able to program them in BASIC was going to change the world."
By 1976, Steve Jobs had convinced product designer Jerry Manock (who had formerly worked at Hewlett Packard) to create the "shell" for the Apple II—a smooth case inspired by kitchen appliances that concealed the internal mechanics.
The first computers went on sale on June 10, 1977 June 10, 1977 was a Friday. bundled with two game paddles (bundled until 1980, when they were found to violate FCC regulations), 4 KiB of RAM, an audio cassette interface for loading programs and storing data, and the Integer BASIC programming language built into ROMs. The original retail price of the computer with 4 KiB of RAM was and with the maximum 48 KiB of RAM, it was 1977 Apple II price list A-VIDD Electronics Co., 1977 Long Beach, CA.
To reflect the computer's color graphics capability, the Apple logo on the casing has rainbow stripes, which remained a part of Apple's corporate logo until early 1998. The Apple II was a significant catalyst for personal computers across many industries; it opened the doors to software marketed at consumers.
The earliest Apple II computers were assembled in Silicon Valley and later in Texas; printed circuit boards were manufactured in Ireland and Singapore.
Overview In the May 1977 issue of Byte, Steve Wozniak published a detailed description of his design; the article began, "To me, a personal computer should be small, reliable, convenient to use, and inexpensive."
The Apple II used peculiar engineering shortcuts to save hardware and reduce costs, such as: Taking advantage of the way the 6502 processor accesses memory: it occurs only on alternate phases of the clock cycle; video generation circuitry memory access on the otherwise unused phase avoids memory contention issues and interruptions of the video stream; This arrangement simultaneously eliminated the need for a separate refresh circuit for DRAM chips, as video transfer accessed each row of dynamic memory within the timeout period. In addition, it did not require separate RAM chips for video RAM, while the PET and TRS-80 had SRAM chips for video; Apart from the 6502 CPU and a few support chips, the vast majority of the semiconductors used were 74LS low-power Schottky chips; Rather than use a complex analog-to-digital circuit to read the outputs of the game controller, Wozniak used a simple timer circuit, built around a quad 555 timer IC called a 558, whose period is proportional to the resistance of the game controller, and he used a software loop to measure the timers; A single 14.31818 MHz master oscillator (fM) was divided by various ratios to produce all other required frequencies, including microprocessor clock signals (fM/14), video transfer counters, and color-burst samples (fM/4). A solderable jumper on the main board allowed to switch between European 50 Hz (PAL) and USA 60 Hz (NTSC) video.
The text and graphics screens have a complex arrangement. For instance, the scanlines were not stored in sequential areas of memory. This complexity was reportedly due to Wozniak's realization that the method would allow for the refresh of dynamic RAM as a side effect (as described above). This method had no cost overhead to have software calculate or look up the address of the required scanline and avoided the need for significant extra hardware. Similarly, in high-resolution graphics mode, color is determined by pixel position and thus can be implemented in software, saving Wozniak the chips needed to convert bit patterns to colors. This also allowed the ability to draw text with subpixel rendering, since orange and blue pixels appear half a pixel-width farther to the right on the screen than green and purple pixels.
The Apple II at first used data cassette storage, like most other microcomputers of the time. In 1978, the company introduced an external -inch floppy disk drive, called Disk II (stylized as Disk ][), attached through a controller card that plugs into one of the computer's expansion slots (usually slot 6). The Disk II interface, created by Wozniak, is regarded as an engineering masterpiece for its economy of electronic components.
The approach taken in the Disk II controller is typical of Wozniak's designs. With a few small-scale logic chips and a cheap PROM (programmable read-only memory), he created a functional floppy disk interface at a fraction of the component cost of standard circuit configurations.
Case design The first production Apple II computers had hand-molded cases; these had visible bubbles and other lumps in them from the imperfect plastic molding process, which was soon switched to machine molding. In addition, the initial case design had no vent openings, causing high heat buildup from the printed circuit board (PCB) and resulting in the plastic softening and sagging. Apple added vent holes to the case within three months of production; customers with the original case could have them replaced at no charge.
Circuit board revisions
The Apple II's printed circuit board (PCB) underwent several revisions, as Steve Wozniak and other Apple engineers made modifications to it. The earliest version was known as Revision 0, and the first 6,000 units shipped used it. Later revisions added a "color killer" circuit to prevent color fringing when the computer was in text mode, as well as modifications to improve the reliability of cassette I/O. Revision 0 Apple IIs powered up in an undefined mode and displayed random characters from memory on-screen, requiring the user to press . This was eliminated in later board revisions. Revision 0 Apple IIs could display only four colors in hi-res mode, but Wozniak was able to increase this to six hi-res colors on later board revisions. (Technically it was eight, but only six were visible.)
There are many revisions of the Apple II circuit board, including revisions 0, 1, 2, 3, 4, 7, and updated versions that are compliant with FCC electromagnetic radiation standards, referred to as "RFI" revisions, including RFI revision 1, revision C, and revision D.
Apple II PCBs have three RAM banks for a total of 24 RAM chips. Original Apple IIs had jumper switches to adjust RAM size, and RAM configurations could be 4, 8, 12, 16, 20, 24, 32, 36, or 48 KiB. The three smallest memory configurations used 4kx1 DRAMs, with larger ones using 16kx1 DRAMs, or mix of 4-kilobyte and 16-kilobyte banks (the chips in any one bank have to be the same size). The early Apple II+ models retained this feature, but after a drop in DRAM prices, Apple redesigned the circuit boards without the jumpers, so that only 16kx1 chips were supported. A few months later, they started shipping all machines with a full 48 KiB complement of DRAM.
Unlike most machines, all integrated circuits on the Apple II PCB were socketed; this cost more to manufacture and created the possibility of loose chips causing a system malfunction, but it was considered preferable to make servicing and replacement of bad chips easier.
The Apple II PCB lacks any means of generating an interrupt request, although expansion cards may generate one. Program code had to stop everything to perform any I/O task; like many of the computer's other idiosyncrasies, this was due to cost reasons and Steve Wozniak assuming interrupts were not needed for gaming or using the computer as a teaching tool.
Display and graphics
Color on the Apple II series uses 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 added later by adding a 3.58-megahertz subcarrier signal that was partially ignored by black-and-white 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. These pulses can translate into pixels on the computer screen, with the possibility of exploiting composite artifact colors.
The Apple II display provides two pixels per subcarrier cycle. When the color burst reference signal is turned on and the computer is attached to a color display, it can display green by showing one alternating pattern of pixels, magenta with an opposite pattern of alternating pixels, and white by placing two pixels next to each other. Blue and orange are available by tweaking the pixel offset by half a pixel-width in relation to the color-burst signal. The high-resolution display offers more colors by compressing more (and narrower) pixels into each subcarrier cycle.