Editing Apple II (original) (section)

==Overview==
In the May 1977 issue of [[Byte (magazine)|''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."<ref name="wozniak197705">{{Cite magazine |last=Wozniak |first=Steve |date=May 1977 |title=System Description / The Apple-II |pages=34–43 |magazine=[[Byte (magazine)|BYTE]] |volume=2 |issue=5 |url=https://archive.org/stream/byte-magazine-1977-05/1977_05_BYTE_02-05_Interfacing#page/n35/mode/2up |access-date=October 17, 2013}}</ref>

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 [[Memory refresh|refresh]] circuit for [[Dynamic random-access memory|DRAM]] chips, as video transfer accessed each row of dynamic memory within the [[Memory refresh#Refresh interval|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&nbsp;MHz master oscillator (f<sub>M</sub>) was divided by various ratios to produce all other required frequencies, including microprocessor clock signals (f<sub>M</sub>/14), video transfer counters, and color-burst samples (f<sub>M</sub>/4). A solderable jumper on the main board allowed to switch between European 50&nbsp;Hz and USA 60&nbsp;Hz 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.<ref>{{Cite web |last=Gibson |first=Steve |title=The origins of sub-pixel font rendering |url=http://www.grc.com/ctwho.htm |url-status=live |archive-url=https://web.archive.org/web/20060721130149/http://www.grc.com/ctwho.htm |archive-date=July 21, 2006 |access-date=August 4, 2006 |publisher=Gibson Research Corporation}}</ref>

The Apple II at first used [[data cassette]] storage, like most other microcomputers of the time. In 1978, the company introduced an external {{frac|5|1|4}}-inch [[floppy disk]] drive, called [[Disk II]] (stylized as Disk ][), attached through a controller card that plugs into one of the computer's [[expansion slot]]s (usually slot 6). The Disk II interface, created by Wozniak, is regarded as an engineering masterpiece for its economy of electronic components.<ref>{{Cite web |last=Weyhrich |first=Steven |date=December 28, 2001 |title=5-The Disk II |url=http://apple2history.org/history/ah05.html |url-status=dead |archive-url=https://web.archive.org/web/20061201122002/http://apple2history.org/history/ah05.html |archive-date=December 1, 2006 |access-date=November 16, 2006 |publisher=Apple II History}}</ref><ref>{{Cite book |last1=Freiberger |first1=Paul |title=Fire In The Valley, Part Two |last2=Swaine |first2=Michael |date=January 1985 |work=A+ Magazine |page=45 |type=Book excerpt |author-link=Paul Freiberger |author-link2=Michael Swaine (technical author)}}</ref>

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.