VisiCalc is credited as being the defining " killer app " in the microcomputer industry. Blue and orange are available by tweaking the offset of the pixels by half a pixel-width in relation to the color-burst signal. Sound[ edit ] Rather than a dedicated sound-synthesis chip, the Apple II has a toggle circuit that can only emit a click through a built-in speaker or a line out jack; all other sounds including two- three- and, eventually, four-voice music and playback of audio samples and speech synthesis are generated entirely by software that clicked the speaker at just the right times.
Similarly, in the high-resolution graphics mode, color is determined by pixel position and can thus be implemented in software, saving Wozniak the chips needed to convert bit patterns to colors.
Rather than use a complex analog-to-digital circuit to read the outputs of the game controller, Wozniak used a simple timer circuit whose period is proportional to the resistance of the game controller, and used a software loop to measure the timer. There is also a third-party card that allows OS-9 Level One to be run.
Perhaps most significantly, the Apple II was a catalyst for personal computers across many industries; it was responsible for opening the doors to software marketed at consumers. All existing customers who sent in their warranty cards were sent free copies of the Red Book.
The Z80 card also allows the connection to a modem and thereby to any networks that the user might have access to. Revision 0 Apple IIs powered up in an undefined mode and had garbage on-screen, requiring the user to press Reset. The earliest version was known as Revision 0, and the first 6, units shipped used it. These patterns are stored in the character generator ROM and replace the text character bit patterns when the computer is switched to low-res graphics mode.
In the early days, these were scarce, but expanded significantly with the development of bulletin board systems. This feature enabled hackers to write and debug machine code programs without needing further development software.
Display and graphics[ edit ] Main article: Early Apple IIs were often sold with a Sup'R'Modwhich allowed the composite video signal to be viewed on a television. Revision 0 Apple IIs could display only four colors, but Wozniak was later able to generate 16 in low-res mode. Color was added on later by adding a 3. The high-resolution display offers more colors by compressing more and narrower pixels into each subcarrier cycle.
As shipped, the machine incorporated a "monitor" program which supported functions such as displaying and altering the contents of the computer's RAM memory in hexadecimal format, either one byte at a time or in blocks of bytes at once. During the first five years of operations, revenues doubled about every four months.
Routines in the ROM encode and decode data in frequency-shift keying for the cassette. The coarse, low-resolution graphics display mode works differently, as it can output a pattern of dots per pixel to offer more color options.
The Apple II display provides two pixels per subcarrier cycle. History[ edit ] BySteve Jobs had convinced the product designer Jerry Manock who had formerly worked at Hewlett Packard designing calculators to create the "shell" for the Apple II — a smooth case inspired by kitchen appliances that would conceal the internal mechanics.
Written by Wozniak, the interpreter enabled users to write software applications without needing to purchase additional development utilities. This was eliminated on the later board revisions. Third-party sound cards greatly improve audio capabilities, allowing simple music synthesis and text-to-speech functions.
Apple added vent holes to the case within three months of production; customers with the original case could have them replaced at no charge.
In addition, the initial case design had no vent openings, causing high heat buildup from the PCB and resulting in the plastic softening and sagging. While mentioning the "oddity" of the artifact colors that produced output "that is not always what one wishes to do", it noted that "no-one has colour graphics like this at this sort of price".
Taking advantage of the way that processor only accesses memory on alternate phases of the clock cycle, the video generation circuitry's memory access on the otherwise unused phase avoids memory contention issues and interruptions of the video stream. The original NTSC television signal specification was black-and-white.
A assembler was soon offered on disk, and later the UCSD compiler and operating system for the Pascal language were made available.
Reception[ edit ] Advertisement for the Apple II Jesse Adams Stein wrote, "As the first company to release a 'consumer appliance' micro-computer, Apple Computer offers us a clear view of this shift from a machine to an appliance.
Written with game programmers and hobbyists in mind, the language only supported the encoding of numbers in bit integer format.
Unlike most machines, all ICs on the Apple II PCB were socketed; although this cost more to manufacture and created the possibility of loose chips causing a system malfunction, it was considered preferable to make servicing and replacement of bad chips easier. This also allows for subpixel font rendering since orange and blue pixels appear half a pixel-width farther to the right on the screen than green and purple pixels.
The Disk II interface, created by Wozniak, is regarded as an engineering masterpiece for its economy of electronic components. The text mode and low-res graphics mode use the same memory region and the same circuitry is used for both.