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Looking for binary representations of 6 bit alphabet  RSS feed

 
Greenhorn
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Anybody know where I can find all the 6 bit binary representations for the letters and other symbols? up to 64 available including the numbers. Not 8 bit binaries but 6 bit

For Example: I know letters A = 110001 I=111001
K=100010 M= 100100 R= 101001 and V= 010011
but thats all I can find.
https://en.wikipedia.org/wiki/BCD_(character_encoding)
shows me some tables but they dont make sense to me.
thanks
 
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What kind of representation are you looking for? BCD is rarely used; ASCII is much more common.
 
Marshal
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. . . and even when I first encountered ASCII in 1971, it used 7 bits not 6.
 
Jim Smithe
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Ya its old NASA data.
I am trying to decode a binary file -data from 1967. They used 6 bit back then on the IBM 7094 mainframe.
For letters and symbols the First 2 bits were "zone bits", which I am still trying to understand, and the next 4 bits were the usual based on 8 4 2 1

After that the next popular model was IBM 360 which then started using 8 bit. Extended BCD.
 
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Jim Smithe wrote:I am trying to decode a binary file -data from 1967. They used 6 bit back then on the IBM 7094 mainframe.



Are you sure that binary data represents characters? If it actually represents numbers then you might be going down the wrong blind alley.
 
Jim Smithe
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You are right Paul. I cant be sure if there are any characters in the data. It could all be numbers.
However I want to know all possibilities just in case. I am kind of hoping there are at least some characters at the top of columns of data to guide me in understanding
some of what the numbers mean that may be listed underneath. ..but like you say No guarantees.
 
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Jim Smithe wrote:I know letters A = 110001 I=111001
K=100010 M= 100100 R= 101001 and V= 010011


This codes could be using one of the Control Data 6-bit codes.  All of your examples match expect for V.  You have 010011, but the CDC coding shows 010101.  Are you you sure your last example is correct?
 
Ron McLeod
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These codes are documented in the Control Data 1604-A Computer Programming Manual, pages 39~43.
 
Campbell Ritchie
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The CDC 1604‑A was introduced in the year 1960. That is a very old encoding.
 
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The Binary Coded Decimal Interchange Code was, indeed a 6-bit code. Because of the limited number of bits it had, there were only a few special characters and no upper/lower case option.

As ancient as I am, the IBM 7000 series was pretty much extinct before I got into serious computer study, but the Extended Binary Coded Decimal Interchange Code was the staple for the IBM System/360 and subsequent mainframes and BCDIC is, as some have noted, embedded within it. Indeed, the programming and data interface for the IBM "green screen" terminals was rather obviously 6-bit based.

You should be able to translate from BCDIC to EBCDIC by simply filling in the leftmost bits of each data element to pad them out to 8 bits. You can see this in the gaps in alphanumeric groups on the famous IBM "Green Card" EBCDIC magic decoder.

Now the fun part is in how you obtained the bits. On Sys/360 equipment, the data might be in 6-bit form, but the I/O controllers returned it already padded to 8 bits. If you got the data raw off the tape, it would probably be 6 bits plus timing and parity bits. Older machines didn't have as much intelligence in the I/O control circuitry, so, for example, they might return a punched-card column as 12 bits, which was then decoded by a library that the programmer would have to include in the application (often by physically shoving a deck of punched-cards into the main program deck.

Storage was VERY expensive back then. A 9-track full-sided 6250 BPI IBM tape reel held only about 150MB and those were high-tech back then. The older machines used lower densities such as 800 BPI. So odds are very high that instead of alphameric data you have binary information. In particular if it was telemetry or captured image data, you'd need specific details on what equipment was intended to read it. Also, data from space probes would typically include some sort of error checking and correcting data of their own (such as Reed-Solomon) because the trip across space is a noisy one and I consider it likely that it wasn't worth the overhead to strip it out.
 
Campbell Ritchie
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Tim Holloway wrote:. . . Also, data from space probes would typically include some sort of error checking and correcting data . . . because the trip across space is a noisy one and I consider it likely that it wasn't worth the overhead to strip it out.

I always thought the reason for leaving the error‑correcting data in space probe information was so the correction could be repeated back on Earth.
 
Tim Holloway
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Campbell Ritchie wrote:

Tim Holloway wrote:. . . Also, data from space probes would typically include some sort of error checking and correcting data . . . because the trip across space is a noisy one and I consider it likely that it wasn't worth the overhead to strip it out.

I always thought the reason for leaving the error‑correcting data in space probe information was so the correction could be repeated back on Earth.



Where else would it have been corrected? All these units could do usually was capture data and transmit it.

But considering the technology of the time it was probably most common to record the data directly to tape as it came in and let downstream processing handle the ECC operations offline. Aside from that, if you got bad data from a moving probe 15 lightt-hours away, it would be kind of difficult to get it to back up and capture another sample anyway.
 
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