Archive for ◊ January, 2011 ◊

27 Jan 2011 Cassette Security
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My first introduction to a microcomputer was a North Star back in 1980, and soon after had my first contact with the Apple II Plus. In both cases, I experienced the benefits of the latest and greatest in data storage and retrieval: The power of the floppy disk. I did not go through any of the trials and travails of those who had to load and save programs and data using cassettes (or, prior to that, paper tape).

Because of the time when I entered the Apple II scene, the whole topic of software cassettes was unknown to me, beyond a vague knowledge that they existed for a short time. In “computer years”, however, a short time can be a very long time. For a full year after the introduction of the Apple II in mid-1977, cassettes were the only way to do data and program storage and retrieval. And even after the Disk II became available in June 1978, at $495 it was not something that all Apple II users immediately purchased and began to use. For the first several years of the life of the Apple II and II Plus, cassettes were used by many, many of those early owners.

Surprisingly, Apple, Inc. still has a page on its support web site that outlines the details of the Apple II cassette interface (part 1 about the format of data on the tape and part 2 about use of the read and write routines from the Monitor, assembly language, and Integer and Applesoft BASIC). Brutal Deluxe, a software company that got its start in the days of the Apple IIGS, has created a web page documenting a collection of as many Apple II programs on cassette as can be discovered. Many of those listed have actually been digitized and are there available for download and execution on an appropriate emulator (such as Gerard Putter’s excellent Virtual ][) or transfer back to a cassette to run on a real Apple II.

Finally, I just discovered Andy McFadden’s excellent technical and programming discussion about the obscure topic of copy protection for cassette software on the Apple II. Everyone who knows about the Disk II on the Apple II and software that was distributed on it is aware of the many software protections schemes that made use of the flexibility that Wozniak built into that device. What I had not previously known was that with some clever programming hacks, early software companies made it difficult for the casual user to copy and share program tapes with others, while retaining the ability to load and run those programs. Some of the programs would not only load but also automatically run without further intervention from the user beyond entering the Monitor command to read data from the cassette!

Again, I am impressed with the power and flexibility that Wozniak built into that wonderful Apple II !

10 Jan 2011 Digging Into The 6502
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The 6502 holds a place of honor amongst the Apple II faithful only slightly lower than that occupied by Steve Wozniak. Apple likes to conclude their press releases with a brief company history that begins with the phrase, “Apple ignited the personal computer revolution in the 1970s with the Apple II”. Well, whether or not the personal computer revolution was truly ignited by Apple may be up for dispute amongst retro computing enthusiasts, but there is no doubt that it was the 6502 from MOS Technology that ignited the imagination of Woz to create the first Apple-1, and later the Apple II. It was as important to Apple as the internal combustion engine was to Henry Ford.

According to an article on Techworld (and reprinted on MacUser), digital archeologists Greg James, Barry Silverman, and Brian Silverman have literally taken the 6502 processor apart, layer by layer. Using this information, they have created a Javascript animation of the function of the 6502, which shows what is happening within the chip as a short machine language program is executed. You can view this animation here at visual6502.org.


Screen shot of part of the visual 6502


Addendum: Thanks to Ken Gagne’s quick eye, here are two more articles about this:

http://research.swtch.com/2011/01/mos-6502-and-best-layout-guy-in-world.html

http://www.youtube.com/view_play_list?p=5396743D539B7755