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KIM-1

Developed by Mos Technology. later acquired by Commodore, to show the possibilities of the 6502 microprocessor but quickly discovered as the first mass-produced personal computer. Easy to extend, lots of detailed documentation. With assembler/editors, first Microsoft Basic on cassette and even a Pascal compiler, it could do a lot. The first have an original Mos Technology logo, later versions have the Commodore logo on the board, small technical differences other than more recent 6502 IC’s without the infamous ROR bug.
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This prehistoric computer has no “real” keyboard and no video output, program are entered by the small hexadecimal keyboard (located in the lower right part of the picture) and results are displayed on the small LED “screen” (it can display only 6 digits). It has a simple monitor that allows one to examine & modify memory, load and save paper tape, load and save cassette tape, run and debug programs through a ‘single step’ mode. The monitor works with the built in keypad and LEDs, or a terminal like the Teletype ASR33. This 20 mA current loop is easy to adapt to RS232C and so any videoterminal can be used.

Information on the KIM-1, also reachable from the menu on the right:

Prototype KIM-1

On team6502  I found a photo of a prototype KIM-1 at MOS Technology, Terry Holdt has this in his office.
The layout is different from the final product, everything seems to be present on this prototype.

MOS Technology 6502

The 6502 CPU, from MOS Technology, has been widely used since its debut in 1975. Designed by a group of people at MOS Technology led by Chuck Peddle, later of Commodore fame, and used in machines like the PET and C64. Also quickly adapted by computer designers like Steve Wozniak in the Apple series, the 1 and ][ and 2 and 2e and 2c and 3. And many others followed!

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For more 6502 IC photos: look at the cpu-collection page.
For an introduction to the 6502 family go to this wikipedia page.
An introduction on the 6502 programming can be found in this wikibook on 6502 assembly.

The 6502 turned out to be an affordable, yet powerful CPU, easy to interface and easy to understand. Many single board computers were designed with the 6502, most often becoming the heart of largely expanded systems.

The KIM-1, developed by MOS technology as a design example, became such a hit. Many were sold, not only to the original target audience, but also to  hobbyists and electronic engineers and system integrators. A new industry was born, based on the microprocessor as the heart of electronic devices. And also the birth of the personal computer, the Apple 2.Nowadays the 6502 is not much more than a memory for most. But the 6502 core is still found in many embedded applications, as sold by the Western Design Centre.

Books in pdf format for download to get started, more books here

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This page is about my interest in retro 8-bit small computer systems computing and electronics. And the role of Dutch electronic magazines like Elektuur and Radio Bulletin in the eighties of the 20th century. Also the Dutch users club, called KIM Gebruikersclub, which I joined in 1978 and contributed to as member of the board and as chief editor of the magazine issue 11 to 25.
The retro computing pages are documenting my experiences with 8-bit systems like the KIM-1 and its relatives such as the Apple 1 and the Junior. And various small Z80 and other systems.
I set up this archive as my personal archive of what I research on the subject. If it is of any use for others, fine, enjoy!

Magazines

In the early days of computing, magazines about popular electronics played a big role in making microprocessors available for the beginner, whether the professional or hobby electric engineer.  The magazines featured here are the dutch magazines Elektuur and Radio Bulletin. From 1977 until 1996 I worked as technical editor for Radio Bulletin and published about microcomputers and more general electronics.  Elektuur published also articles on these subjects, many are available here.

What is a SBC for me?

A SBC, short for Single Board Computer can be defined as a computer system, based on a microprocessor, on one printed circuit, with keyboard and display, programmable I/O ports, expansion connectors and without a casing. The ‘operating system’ is stored in a (EP)ROM, an often small amount of RAM is available to store programs and data These were the first microprocessor based computers with affordable prices for hobbyists in the late seventies of the previous century. For professionals a way of getting acquainted with the new hardware and learning the basics of programming at a (very!) low level.

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Though it is a complete computer, it has a CPU, memory and I/O, it is also a very limited one. The I/O is often not more than a small keyboard with hexadecimal functions. The display is often not more than 6 or 8 seven segment LED displays, just enough to show, in hexadecimal format, addresses and data. The operating system allows entering and examining of data in memory locations, and start and stop a program. Loading and saving data is limited to either papertape readers and punches, quite common in these days, or via some modulation as data files on audio cassette recorders. Also common is the ability to attach a teletype like the ASR33.

A good example of such a SBC is the KIM-1, shown below. 2K ROM, 1K RAM, many I/O lines free, six LED displays and a keyboard with hexadecimal keys and some function keys.
Why these SBCs like the KIM-1 became so popular? One reason was the low price ($ 280 for a KIM-1, I paid 795 guilders ), so it was in the price range of the average student and hobbyist. Another is the design being open, the complete hardware description and detailed listing of the ROM was included. And it is not the frightening computer, but more a programmable piece of hardware. Because it was so easy accessible and low speed, adding and changing hardware is not hard also. Programming was not easy, but editors/assemblers that could run with some added hardware like RAM and a video terminal made that possible. The nowadays common practice of cross compiling was not available for the hobbyist then.

Besides playing with the SBC, to learn what the microprocessor is capable of, many SBCs were put to work as a sort of PLC, controlling devices in the real world.
What changed the popularity of SBCs was the wish to transfer it to a computer with a better user interface, like graphics on a video screen, a full blown keyboard, a real operating system with mass storage such as floppy drives, and a higher fun factor, a.k.a. games. Or to make it a serious computer fit for business. So SBCs became extinct fast in the mainstream hobby world when the hobbycomputer appeared on the market, like the TRS-80, PET and later the C-64, MSX etc. Even later the boring business PC killed the hobby computer, but that is another story.
It seems the SBC’s are back though: Arduino and Raspberry Pi and the availability of cheap Chinese electronic shops and cross compilation on the PC make it possible to play affordable with small programmable devices at a lower level.

This site is mostly specialized on the 6502 and Z80 SBC (Single Board Computer), small computers based on an 8 bit microprocessor. Good for learning about digital electronics and programming at a lower level. And for many the start of their career in computer science.
SBCs featured here are systems like KIM-1, Apple 1 and equivalent boards like the A-ONE, Apple 1 Replica, Micro-KIM, Elektor Junior, AIM-65, SYM-1, RC2014, TEC-1, MBC-2 and such.

Please use the Contact form to contribute to this fascinating hobby!
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