Working Apple I nets record-smashing $640,000
12-12-2012, 03:43 AM
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Working Apple I nets record-smashing $640,000
12-12-2012, 03:28 PM
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'70s personal computers had the crapiest data storage. It was a real fussy thing, and you had to use it because they had small internal memory. I recall the Radio Shack Tandy TRS-80, a simple early pc.
Cassette tape drive
User data was originally stored on cassette tape. Radio Shack's model CTR-41 cassette recorder was included with the $599 package. The cassette tape interface was very slow and erratic; it was sensitive to audio volume changes, and the machine only gave the very crudest indication as to whether the correct volume was set, via a blinking character on screen when data was being loaded. To find the correct volume, one would sometimes have to attempt to load a program once adjusting volume until the machine picked up the data, then reset the machine, rewind the tape and attempt the load again. Users quickly learned to save a file three or more times in hopes that one copy would prove to be readable. Automatic gain control or indicator circuits could be constructed to compensate for this (the owner's manual provided complete circuit diagrams for the whole machine, including the peripheral interfaces, with notes on operation).
An alternative tape interface could receive transmissions from the BBC's Chip Shop programme in the UK, which broadcast software for several different microcomputers over the radio. A special program (loaded using the conventional tape interface) was needed to access the custom interface. Tandy eventually replaced the CTR-41 unit with the CTR-80 which had built-in AGC circuitry (and no volume control). This helped the situation, but tape operation was still unreliable. TRS-80s with Level I BASIC read and wrote tapes at 250 bits per second (31.25 bytes per second); Level II BASIC doubled this to 500 bits per second (62.5 bytes per second). Some programmers wrote machine language programs that would increase the speed to up to 1800 bits per second without loss in reliability.
For loading and storing data, no hardware controller existed. Instead, the processor created the sound itself by switching the output voltage between three states, creating very crude sine wave audio.The first models of the Model I also had problems reading from the cassette drives. Tandy eventually offered a small board which was installed in a service center to correct earlier models. The ROMs in later models were modified to correct this...
From Wikpedia Tandy TRS-80 article
Cassette tape drive
User data was originally stored on cassette tape. Radio Shack's model CTR-41 cassette recorder was included with the $599 package. The cassette tape interface was very slow and erratic; it was sensitive to audio volume changes, and the machine only gave the very crudest indication as to whether the correct volume was set, via a blinking character on screen when data was being loaded. To find the correct volume, one would sometimes have to attempt to load a program once adjusting volume until the machine picked up the data, then reset the machine, rewind the tape and attempt the load again. Users quickly learned to save a file three or more times in hopes that one copy would prove to be readable. Automatic gain control or indicator circuits could be constructed to compensate for this (the owner's manual provided complete circuit diagrams for the whole machine, including the peripheral interfaces, with notes on operation).
An alternative tape interface could receive transmissions from the BBC's Chip Shop programme in the UK, which broadcast software for several different microcomputers over the radio. A special program (loaded using the conventional tape interface) was needed to access the custom interface. Tandy eventually replaced the CTR-41 unit with the CTR-80 which had built-in AGC circuitry (and no volume control). This helped the situation, but tape operation was still unreliable. TRS-80s with Level I BASIC read and wrote tapes at 250 bits per second (31.25 bytes per second); Level II BASIC doubled this to 500 bits per second (62.5 bytes per second). Some programmers wrote machine language programs that would increase the speed to up to 1800 bits per second without loss in reliability.
For loading and storing data, no hardware controller existed. Instead, the processor created the sound itself by switching the output voltage between three states, creating very crude sine wave audio.The first models of the Model I also had problems reading from the cassette drives. Tandy eventually offered a small board which was installed in a service center to correct earlier models. The ROMs in later models were modified to correct this...
From Wikpedia Tandy TRS-80 article
12-12-2012, 09:03 PM
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