The Tarbell Cassette Interface is an expansion card for use with the Altair 8800 early personal computer, or other systems using the Altair's S-100 bus. It was designed by Don Tarbell [1] and sold by Tarbell Electronics starting in 1976. [2] At the time, it was considered to be fast, reliable, and popular, and became a de facto standard for compact cassette data storage. [3] [4]
The Tarbell format is essentially Manchester encoding where a "1" bit in the original data is output as "01", and a "0" bit is output as "10". This is accomplished by reading a byte into a shift register which is periodically triggered by a 555 timer. Although the system can be run at any audible frequency, it is normally set to 3,000 Hz. As each data bit requires two output bits, the effective data rate is 1,500 bits per second, or 187 bytes per second. On reading, the system uses clock recovery to calculate the original data rate to account for tape stretch and other effects. This means the data can be recorded at any hardware-supported rate, and the manual suggests up to 560 bytes per second. [5]
At the time of its release in 1976, the 300 bits per second Kansas City standard was also in use. Tarbell later modified the system to support these tapes. This increases the main oscillator from its normal 3,000 Hz to 4,800 Hz, and then writing either 00000000 to produce a single "1", or 01010101 to produce a "0". Because the system divides the basic rate by two, and each bit requires eight outputs, this produces the standard 300 bits per second output of the Kansas City standard. [5]
Tarbell also sold other products, including TARBELL CASSETTE BASIC in 1978 [6] and a Shugart Associates-compatible dual disk drive subsystem. The latter includes a Tarbell floppy disk interface, said to plug into any S-100 bus computer, introduced in 1979. [7]
In computer architecture, a bus is a communication system that transfers data between components inside a computer, or between computers. This expression covers all related hardware components and software, including communication protocols.
The 6800 is an 8-bit microprocessor designed and first manufactured by Motorola in 1974. The MC6800 microprocessor was part of the M6800 Microcomputer System that also included serial and parallel interface ICs, RAM, ROM and other support chips. A significant design feature was that the M6800 family of ICs required only a single five-volt power supply at a time when most other microprocessors required three voltages. The M6800 Microcomputer System was announced in March 1974 and was in full production by the end of that year.
The KIM-1, short for Keyboard Input Monitor, is a small 6502-based single-board computer developed and produced by MOS Technology, Inc. and launched in 1976. It was very successful in that period, due to its low price and easy-access expandability.
The Altair 8800 is a microcomputer designed in 1974 by MITS and based on the Intel 8080 CPU. Interest grew quickly after it was featured on the cover of the January 1975 issue of Popular Electronics and was sold by mail order through advertisements there, in Radio-Electronics, and in other hobbyist magazines. According to Harry Garland, the Altair 8800 was the product that catalyzed the microcomputer revolution of the 1970s. It was the first commercially successful personal computer. The computer bus designed for the Altair was to become a de facto standard in the form of the S-100 bus, and the first programming language for the machine was Microsoft's founding product, Altair BASIC.
The S-100 bus or Altair bus, IEEE 696-1983(inactive-withdrawn), is an early computer bus designed in 1974 as a part of the Altair 8800. The S-100 bus was the first industry standard expansion bus for the microcomputer industry. S-100 computers, consisting of processor and peripheral cards, were produced by a number of manufacturers. The S-100 bus formed the basis for homebrew computers whose builders implemented drivers for CP/M and MP/M. These S-100 microcomputers ran the gamut from hobbyist toy to small business workstation and were common in early home computers until the advent of the IBM PC.
The Kansas City standard (KCS), or Byte standard, is a data storage protocol for standard cassette tapes or other audio recording media at 300 bits per second. It originated in a symposium sponsored by Byte magazine in November 1975 in Kansas City, Missouri to develop a standard for the storage of digital microcomputer data on inexpensive consumer quality cassettes. The first systems based on the standard appeared in 1976.
"An Open Letter to Hobbyists" is a 1976 open letter written by Bill Gates, the co-founder of Microsoft, to early personal computer hobbyists, in which Gates expresses dismay at the rampant software piracy taking place in the hobbyist community, particularly with regard to his company's software.
The Commodore 1530 (C2N) Datasette, later also Datassette, is Commodore's dedicated magnetic-tape data storage device. Using compact cassettes as the storage medium, it provides inexpensive storage to Commodore's 8-bit computers, including the PET, VIC-20, and Commodore 64. A physically similar model, Commodore 1531, was made for the Commodore 16 and Plus/4 series computers.
Micro Instrumentation and Telemetry Systems, Inc. (MITS), was an American electronics company founded in Albuquerque, New Mexico that began manufacturing electronic calculators in 1971 and personal computers in 1975.
Processor Technology Corporation was a personal computer company founded in April 1975, by Gary Ingram and Bob Marsh in Berkeley, California. Their first product was a 4K byte RAM board that was compatible with the MITS Altair 8800 computer but more reliable than the MITS board. This was followed by a series of memory and I/O boards including a video display module.
The TV Typewriter is a video terminal that could display two pages of 16 lines of 32 upper case characters on a standard television set. The design, by Don Lancaster, appeared on the cover of Radio-Electronics magazine in September 1973.
The Sol-20 was the first fully assembled microcomputer with a built-in keyboard and television output, what would later be known as a home computer. The design was the integration of an Intel 8080-based motherboard, a VDM-1 graphics card, the 3P+S I/O card to drive a keyboard, and circuitry to connect to a cassette deck for program storage. Additional expansion was available via five S-100 bus slots inside the machine. It also included swappable ROMs that the manufacturer called 'personality modules', containing a rudimentary operating system.
The Dick Smith Super-80 was a Zilog Z80 based kit computer developed as a joint venture between Electronics Australia magazine and Dick Smith Electronics.
Heathkit's H8 is an Intel 8080A-based microcomputer sold in kit form starting in 1977. The H8 is similar to the S-100 bus computers of the era, and like those machines is often used with the CP/M operating system on floppy disk.
The Cromemco Dazzler was a graphics card for S-100 bus computers introduced in a Popular Electronics cover story in 1976. It was the first color graphics card available for microcomputers. The Dazzler was the first of a succession of increasingly capable graphics products from Cromemco which, by 1984, were in use at 80% of all television stations in the U.S. for the display of weather, news, and sports graphics.
The original IBM Personal Computer and IBM PCjr included support for storing data and programs on compact cassette tape.
The Serial Input/Output system, universally known as SIO, was a proprietary peripheral bus and related software protocol stacks used on the Atari 8-bit computers to provide most input/output duties for those computers. Unlike most I/O systems of the era, such as RS-232, SIO included a lightweight protocol that allowed multiple devices to be attached to a single daisy-chained port that supported dozens of devices. It also supported plug-and-play operations. SIO's designer, Joe Decuir, credits his work on the system as the basis of USB.
PolyMorphic Systems was a manufacturer of microcomputer boards and systems based on the S-100 bus. Their products included the Poly-88 and the System 8813. The company was incorporated in California in 1976 as Interactive Products Corporation d/b/a PolyMorphic Systems. It was initially based in Goleta, then Santa Barbara, California.
Parasitic Engineering, Inc., was an American computer company founded by Howard Fullmer and Gene Nardi in 1974. Named as a tongue-in-cheek reference to a comment by MITS co-founder Ed Roberts, Parasitic's first products were hardware upgrade kits to MITS' Altair 8800 microcomputer kit, improving the latter's power supply rating and susceptibility to noise. The company later released their own microcomputer based on the same bus as the Altair, the S-100, but it was less popular than the company's hardware-improvement kits. By 1979, the company had pivoted to providing upgrades to Tandy's TRS-80. Parasitic went defunct in 1983.
My name is Paula Rouse. I worked for the "Famous" Don Tarbell at Tarbell Electronics in Carson, CA from 1976 to 1983. I was his first employee when he began selling cassette interface kits and assembled units. He was a terrific boss and his wife Brenda and I have been best friends for all these years. She called me this evening to say that Don passed away this morning, May 19th, 1998, after a long bout with cancer.