Re: [USMA:38926] Re: Discussion on the metric systemBill et al:
Although this may be fundamentally off the metric topic, it has a direct
bearing on why developing, learning and using the SI is so important.
The SI is coherent, simple and compatible. And, the SI standard helps to
reduce costs of learning, production and operations. The SI can and does
improve efficiency when understood and applied correctly. The new quadlitre
milk jug is a prime example. The manufacturing of cars which now are designed
and built in metric is another prime example. And there are many more
examples. The US is going metric very subtlely and consumers don't care until
arm-waving less knowledgeable media or those with an agenda intervene to try to
stop it. Those people just aggravate the issue unnecessarily.
BCD is "binary coded decimal" which IBM and other computer companies use
to pack two decimal digits into one 8-bit byte for efficiency purposes. Some
inexpensive calculators use this today. However, that became the basis for
using 8-bits to represent various characters and functions. The five-bit
Baudot codes were used as the basis for the ASCII codes since the shift bit was
added to the 5-bits to represent upper and lower case characters, numbers and
functions. Six bits were used initially since computer words were in 6-bit
increments until the 8-bit-based words were invented for packed decimal
efficiency and to make available more codes for more character sets.
Computers have been growing from 8-bit to 16-bit to 32-bit to 64-bit and to
128-bit machines to meet the increasing demand for precision, HD displays,
video and for computation, TV and game applications.
The length of the start and stop bits is irrelevant to information coding
schemes except to define the length and separation of characters during
transmission. The start and stop bits were used for asynchronous
transmission. They were eliminated for synchronous transmission to increase
thruput (available information transfer time). During the late 1960s I
designed and implemented a KCRT synchronous transmission and display system
for weather rather than use asynchronous because I could get 3000 words per
minute for synchronous versus 2000 WPM for asynchronous over the same
transmission facilities economically. A character check bit was added to the
coding scheme and used during the transition from Baudot to synchronous
transmissions. As computer technology advanced and costs became less, complex
longitudinal and lateral computations on transmitted bits were used to replace
the check bits for transmission error detection and correction and to increase
thruput.
The A, B, C, D etc you mention are represented by the binary equivalent
decimals of 1, 2, 3, 4 etc.up to 31 (32 numbers including zero) in the 5-bit
code and 15 in the 4-bit binary coding scheme for BCD. They occupy the
right-most (least significant bit) positions in the coding scheme as you
indicate. The sixth bit was needed to provide for lower case and special
characters. Therefore, the left-most bits could be stripped in processing and
the right-most (least significant bits) could be used to represent a, b, c, d,
etc regardless of case and still retain some base-intelligence. That technique
is still used today in the Internet for characters which are not case
sensitive. (Names to the left of the @ sign in email addresses.) When the
8-bit characters became available, complete foreign character sets and
special character sets were invented and are used today.
Coding compatibility was a major issue to contain manufacturing costs while
upgrading teletypewriter systems from Baudot to ASCII machines and to minimize
conversion operations within computers.
Regards, Stan Doore
----- Original Message -----
From: Bill Potts
To: U.S. Metric Association
Sent: Monday, July 23, 2007 3:59 AM
Subject: [USMA:39153] Re: Discussion on the metric system (off topic -- of
course)
Stan:
This is the statement with which I have a problem: "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."
I can understand (intellectually, but not practically) the creation of a 7-
or 8-bit code in which, say, the five low-order bits are ITA-2 code points.
However, such a code is not ASCII (or EBCDIC). In ITA-2 code (in which letters
are upper-case only, as they were in BCD), A, B, C and D are 11000 (24), 10011
(19), 01110 (14), and 10010 (18), respectively. They are not even in ascending
sequence and, of course, those same codes are used in Figures Shift mode for =,
?, :, and $. In ASCII, the five low-order bits of the codes for A, B, C and D
are 00001, 00010, 00011, and 00100, respectively. So there's no correspondence
at all.
The older ("Telex") and the newer (TWX) teletype machines were not, in fact,
compatible. As their public networks were owned by competing companies (Western
Union and AT&T, I believe), compatibility wasn't much of an issue. Devices
(typically computer peripherals) were built that could handle any 5, 6, 7 or
8-bit paper tape, using any code (determined by the software controlling them).
I managed a computer service bureau, in 1971, where our RJE (Remote Job Entry)
terminal had paper tape capabilities, including 6-level tape containing output
from cash registers. Incidentally, when connected to computer-based networks,
Telex and TWX terminals were able to benefit from the code conversion
capabilities of the computer software.
By the way, you may have missed my reference to 36-bit words in message 38931.
Best regards,
Bill Potts
SI Navigator (http://metric1.org)
----------------------------------------------------------------------------
From: STANLEY DOORE [mailto:[EMAIL PROTECTED]
Sent: Monday, July 23, 2007 00:13
To: [EMAIL PROTECTED]; U.S. Metric Association
Subject: Re: [USMA:39147] Re: Discussion on the metric system (off topic --
of course)
Thanks 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).
