Re: [USMA:38926] Re: Discussion on the metric systemThanks Bill for the very
detailed technical explanation.
I wasn't trying to belabor the point, but only to tell how the eight-bit
ASCII code was adopted in practice. The five bits of the Baudot code are
incorporated into the eight-bit ASCII code to ensure compatibility between the
old and new teletype machines and to use ASCII internally to computers like we
now have in PCs etc.
Word length in early IBM computers were 36 bits which is not divisible by
8 (ASCII). That's why the 16-bit, 32-bit, 64-bit and 128-bit (PlayStations
and supercomputers) word machines were created for compatibility.
Now that manufacturing of longer word machines is becoming less expensive
and necessary and the need for intense image and video processing, industry is
moving to longer word machines. This is necessary as new technology and high
definition TV come onto the market and discs like the BluRay which have a
capacity of 50 GBytes are necessary.
Regards, Stan Doore
----- Original Message -----
From: Bill Potts
To: U.S. Metric Association
Sent: Sunday, July 22, 2007 8:25 PM
Subject: [USMA:39147] Re: Discussion on the metric system (off topic -- of
course)
Stan:
I'm afraid I must respectfully disagree with you about Baudot Code. The
five-bit code used for teletype machines was a 1930 variant, called ITA-2
(International Telegraph Alphabet No. 2). TWX (TeletypeWriter eXchange)
machines used ITA-5, otherwise known as ASCII. I will acknowledge, though, that
ITA-2 was known colloquially as Baudot Code. (See
http://groups.msn.com/CTOSeaDogs/baudotcode1.msnw.)
However, that disagreement is really only semantic. More important is that
there is no relationship between the 5-bit codes and either 7- or 8-bit ASCII
(i.e., ASCII is not an extension of ITA-2, as even a cursory examination of the
two code tables will show). With the 5-bit codes, the meaning depended on
whether the device was in Letters Shift or Figures Shift mode-and, of course,
two of the code points were used for effecting the shift. One of the virtues of
ASCII and EBCDIC (and previously, of BCD) is that, for a given natural
language, every code point is unique and there's no possibility of getting a
garbled message because of being in the wrong shift mode. Seven-bit ASCII
includes Shift Out and Shift In code points, used to change the character
associated with some of the alphanumeric code points. I've never worked with an
actual implementation of that, though.
Another feature of ASCII and EBCDIC is the dedication of the lower-value code
points to control functions (0 to 31 [hex 1F] for ASCII, 0 to 63 [hex 3F] for
EBCDIC). Other than Letters Shift, Figures Shift, Carriage Return, Line Feed,
and Space, ITA-2 had no assigned control code points. The ones I've mentioned
were independent of the shift mode and, therefore, could legitimately be called
control codes. As BEL (bell) was simply the Figures Shift counterpart of the
letter S (i.e., same code point, different shift status), it can't be
considered a control code.
Best regards,
Bill Potts
SI Navigator (http://metric1.org)
----------------------------------------------------------------------------
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of STANLEY DOORE
Sent: Sunday, July 22, 2007 15:06
To: U.S. Metric Association
Subject: [USMA:39145] Re: Discussion on the metric system (off topic -- of
course)
Hi Bill et al:
Sounds like you and I came from the same era (circa 1958) of punched
cards. I was on the US federal advisory committee for standardizing on the
eight-bit ASCII code. We selected the eight-bit ASCII code as the base even
though IBM wanted a BCD-based system.
At the time, the whole world used the five-bit baudot code in
communications and Digital Equipment Corporation computers used an extension of
it (ASCII) internal to their computers. It meant that the conversion would be
less stressful, less complex and more compatible by expanding the five-bit
baudot code to the eight-bit ASCII code for various reasons Including the
accommodation of international and special characters for both communications
and computers. Eight bits became a byte in computers now used today while six
bits were used to represent characters in early machines of IBM etc.
Regards, Stan Doore
----- Original Message -----
From: Bill Potts
To: U.S. Metric Association
Sent: Saturday, July 21, 2007 4:20 PM
Subject: [USMA:39118] Re: Discussion on the metric system (off topic --
of course)
Stan:
Please excuse the delayed response. I only visit this list occasionally
these days.
Although this business of codes is obviously somewhat off-topic, it's
interesting, especially to those of us concerned with the niceties of the
metric system and therefore of the view (probably, but not necessarily) that
there's no such thing as an uninteresting number (or, apparently, code).
The interesting thing about EBCDIC is that, as with the old 6-bit BCD,
there's a direct correspondence between the encoding of any given character and
its representation, as punch holes, on the now-obsolete punch cards. Every one
of the 256 values has a corresponding set of punch holes. And, of course, as
the punch card came first, EBCDIC code points are based on that, rather than
the other way around.
Used to the maximum, the 12 rows of a punch card column could, of course,
accommodate 4096 unique values. IBM's "scientific" 7000 series computers used
row binary to take advantage of that, with the first 72 columns of one card
being able to store the contents of twenty-four 36-bit words.
However, although looking back is fun, I'm glad technology has moved on.
I've never missed those days of humping ten-thousand-card cartons of punch
cards around the computer room (or the card jams or the dropped cards).
Bill
------------------------------------------------------------------------
From: G Stanley Doore [mailto:[EMAIL PROTECTED]
Sent: Wednesday, June 20, 2007 10:20
To: [EMAIL PROTECTED]; U.S. Metric Association
Subject: Re: [USMA:38932] Re: Discussion on the metric system
Thanks Bill for the correction and further explanation.
EBCDIC was invented to use the full 8 bits for expanded representations.
Stan Doore
----- Original Message -----
From: Bill Potts
To: U.S. Metric Association
Sent: Tuesday, June 19, 2007 4:33 PM
Subject: [USMA:38932] Re: Discussion on the metric system
Stan Doore wrote: "IBM invented the hexadecimal to provide for all
types of international characters and many special symbols."
Not quite. For that purpose, they invented and introduced EBCDIC
(Extended Binary Coded Decimal Interchange Code), for which the unit was/is the
byte, defined as a group of 8 bits. Because the three-bit grouping of the octal
notation was potentially awkward, they introduced four-bit [half byte]
hexadecimal notation, which already existed conceptually, but had no practical
application in the days of computers with 36-bit word sizes (e.g., the IBM
7090). Any EBCDIC value was thus expressible as 2 hexadecimal digits (as was,
eventually, any 8-bit ISO 646 [ASCII in the US] value).
Of course, it was still awkward, in that we all had to learn to use A
through F for the six four-bit groupings beyond the one expressed as 9.
Code points in today's 16-bit Unicode are, of course, expressible as
strings of four hexadecimal digits.
Bill Potts
(whose first experience with a computer was on the Burroughs E101
Desk Size Engineering Computer, with its 256 10-digit decimal words on a drum,
plugboard programming, and a contemporary accounting-machine numerals-only
print mechanism).
