Hmm...

[intvnut]

One more comment on the Keyboard Component tape format: It's one of the most heavily engineered tape formats of its era. It's got some really heavy duty stuff going on. Some bullet points:

• Manchester encoded bits
  
• Special, durable framing at two frequencies to allow identifying block boundaries even when seeking
  
• Hardware dropout detection to aid error recovery
  
• Detect-2, Correct-1 Hamming code (also called SECDED) applied on 10-bit values (15-bit code), divided into blocks of 32 interleaved words, to spread dropouts across multiple Hamming-protected words. Dropout detection information gets used in the 2-error case to allow attempting to fix those errors also.
  
• Dropout-resistant time code sequence for synchronizing audio blocks with program code
  

It's like they tried to take one of those minicomputer reel-to-reel block addressable tape units and shrink it into the Keyboard Component.

 

Compare this to, say, the Kansas City Standard, which was basically just playing half of a 300 or 1200 baud FSK modem at the tape drive.

Edited September 17, 2012 by intvnut

[Intymike]

The Keyboard Component may actually require preformatted cassettes.

 

Keyboard Component tapes are the same mechanically as regular stereo cassette tapes, but the read/write head setup is different. Instead of two pairs of stereo tracks going opposite directions, the Keyboard Component treats it as 4 tracks all going the same direction. One pair of tracks is read-only, and the other pair is read-write. There's a read-only data track and a read-only analog track for sound, music and prerecorded voice. Likewise, there's a read-write data track and a read-write analog track. The read-only and read-write analog tracks are how Conversational French does its magic of, saying a phrase, sampling you saying it and playing your voice back to you.

 

The cassette unit is completely automated and block addressable. You may have noticed looking at the Keyboard Component that there are no buttons to operate the tape drive. Instead, the data sectors contain special headers that encode block boundaries and block identifiers. They're actually encoded twice at two frequencies so that the block boundaries can be identified while the tape's being fast-forwarded. (I think it can also detect them during rewind, but I'm not sure. Frank may know.)

 

The block boundaries define the pacing for all the tracks, including the audio portions. If you want to play a specific piece of audio, you specify which data block it starts at in order to seek to the right spot. The data tracks that go in parallel to audio portions are encoded specially with a unique time-code sequence that allows software to correctly synchronize with the audio regardless of whether the tape has stretched or there's variations in the tape drive motor speed. (Google around for "PicSee", which is the name David Rolfe gave to this synchronizing approach.)

 

Now here's where it gets a little fuzzy: I think all the block boundaries are all defined solely based on the read-only data track for consistency purposes. I'm pretty sure that was the case. If that is indeed true, then yes, you need special preformatted cassettes, since it's not physically possible for the Keyboard Component to format the cassette for you. From what I remember, it does not have write heads for the two read-only tracks.

 

Frank Palazzolo would likely be able to say for sure whether the KC had the ability to format a cassette. My memory is that it did not. In a sense, it's a little like "hard sectoring", only without an optical mark for the sector boundaries.

 

Wow, that sounds like the most advanced cassette system ever!

 

It´s good that I could use a normal cassette player and cassettes for the ECS. This way I was able to type your Simon Sez game in and saved it on tape.

[+DZ-Jay]

 

The Keyboard Component may actually require preformatted cassettes.

 

Ah, that makes sense, since the read-only tracks could not be formatted from the KC, as you mention later on in your post.

 

Keyboard Component tapes are the same mechanically as regular stereo cassette tapes, but the read/write head setup is different. Instead of two pairs of stereo tracks going opposite directions, the Keyboard Component treats it as 4 tracks all going the same direction.

 

How is this different from 4-track cassette "mini-studio" recorders? I had a TASCAM one and it used standard cassettes.

 

Doesn't that depend only on the way the read/write head is operated?

 

I'm genuinely curious.

[intvnut]

How is this different from 4-track cassette "mini-studio" recorders? I had a TASCAM one and it used standard cassettes.

 

Well, the cassette itself is standard. It's being used in a unique way that is rather similar to the 4-track TASCAM you mention. But, instead of 4 audio tracks, it's 2 audio, 2 data.

 

Doesn't that depend only on the way the read/write head is operated?

 

I'm genuinely curious.

 

As I recall, tape heads are in principle reversible: that is, you can use the same head for writing as for reading. In the KC hardware, though, I don't believe a provision was made to allow the fixed tracks to be written in its electronics.

 

Also, I don't remember if the KC has a separate erase head or not. Erase heads can improve the quality of a recording by more completely eliminating the prior signal. They're also part of the reason why, on recorders that use them, you can't seamlessly overwrite something (unless the recorder's electronics are more sophisticated than the cheap recorders I grew up with). Rather, there's always a slight gap, corresponding to the distance between the erase head and the read/write head.

 

Frank would know for sure if the KC had a separate record or erase head. I honestly don't know / remember. I do distinctly recall him saying there was no provision in the KC to write to two of the four tracks.

 

 

[intvnut]

Frank would know for sure if the KC had a separate record or erase head. I honestly don't know / remember. I do distinctly recall him saying there was no provision in the KC to write to two of the four tracks.

 

BTW, I did find the last copy of his notes that he had sent me. Relevant excerpts:

 

* Side A is pre-recorded, Side B can be recorded over

* The hardware lacks the ability to specify overwriting side A entirely. It has four modes specified in 2 bits: "Read B-side data", "Read A-side data", "Write B-side data", "Write B-side audio".

* There's a bit marked "Tied to Erase Head? (TBD)" which suggests there is an erase head.

 

So there you go.

 

[+DZ-Jay]

 

BTW, I did find the last copy of his notes that he had sent me. Relevant excerpts:

 

* Side A is pre-recorded, Side B can be recorded over

* The hardware lacks the ability to specify overwriting side A entirely. It has four modes specified in 2 bits: "Read B-side data", "Read A-side data", "Write B-side data", "Write B-side audio".

* There's a bit marked "Tied to Erase Head? (TBD)" which suggests there is an erase head.

 

So there you go.

 

Perfect! That answers the question: the KC requires pre-formatted tapes.

 

However, to my original point, since the KC is so rare, and most of the surviving ones don't even have a working tape drive, anybody could auction off a regular music tape with a custom label slapped on. And who would know the difference.

 

Thanks!

Edited September 17, 2012 by DZ-Jay

[+cmart604]

 

 

Perfect! That answers the question: the KC requires pre-formatted tapes.

 

Thanks!

 

But it doesn't answer the question of whether I should buy that tape or not.

[Intymike]

But it doesn't answer the question of whether I should buy that tape or not.

 

If you buy it you never would use it because it´s that damn expensive!

 

But you want it...

[+cmart604]

 

 

If you buy it you never would use it because it´s that damn expensive!

 

But you want it...

 

Lol! True.

[intvnut]

Perfect! That answers the question: the KC requires pre-formatted tapes.

 

Well, I'm not sure it does. The notes indicate that the header tone appears in parallel on all four channels, though, and the digital channel locks to it. It didn't say which digital channel; it could be that either digital channel can lock to it, in which case it's conceivably possible that KC BASIC can format a data cassette.

 

However, to my original point, since the KC is so rare, and most of the surviving ones don't even have a working tape drive, anybody could auction off a regular music tape with a custom label slapped on. And who would know the difference.

 

I wonder if there's some way to tell through, say, the write protect notch or other case attribute? For example, the recording bias, write protect status and other details are encoded with various notches in the case. Or, at least they were by the end of the 80s. The earlier tapes lacked these, I believe. You'd have to find a suitably old tape that lacked some of these features.

 

If the write-protect notch is open (which I believe they are on KC cassettes to prevent over-writing in a regular recorder), you'd have to start with a prerecorded music cassette rather than a consumer cassette, since consumer cassettes would have either a knock-out tab or a slider there.

 

Finally, if you compare to an official tape, it should have a certain amount of tape on it total. (This can be measured in any tape deck by fast-forward / rewind.) So, in principle you could validate that the correct length of tape is in the cassette.

 

Hmmm... maybe if my engineering career peters out, I should consider forensics.

Edited September 17, 2012 by intvnut

[intvnut]

Well, I'm not sure it does. The notes indicate that the header tone appears in parallel on all four channels, though, and the digital channel locks to it. It didn't say which digital channel; it could be that either digital channel can lock to it, in which case it's conceivably possible that KC BASIC can format a data cassette.

 

Here's another thought, though: If you're careful, it seems like you should be able to dub an official blank onto another blank to "format" it. I wonder how aligned the header tones need to be across all four tracks?

[+DZ-Jay]

 

Well, I'm not sure it does. The notes indicate that the header tone appears in parallel on all four channels, though, and the digital channel locks to it. It didn't say which digital channel; it could be that either digital channel can lock to it, in which case it's conceivably possible that KC BASIC can format a data cassette.

 

 

 

I wonder if there's some way to tell through, say, the write protect notch or other case attribute? For example, the recording bias, write protect status and other details are encoded with various notches in the case. Or, at least they were by the end of the 80s. The earlier tapes lacked these, I believe. You'd have to find a suitably old tape that lacked some of these features.

 

If the write-protect notch is open (which I believe they are on KC cassettes to prevent over-writing in a regular recorder), you'd have to start with a prerecorded music cassette rather than a consumer cassette, since consumer cassettes would have either a knock-out tab or a slider there.

 

Finally, if you compare to an official tape, it should have a certain amount of tape on it total. (This can be measured in any tape deck by fast-forward / rewind.) So, in principle you could validate that the correct length of tape is in the cassette.

 

Hmmm... maybe if my engineering career peters out, I should consider forensics.

 

All that just means that *you* wouldn't fall for it.