All these modems take an incoming bit stream and convert it to a series of
line symbols on the wire (or fiber or radio wave). These line symbols are
designed to be easy to tell apart, even after having been distorted and
corrupted a bit on the line, so the receiving modem can tell with very high
reliability which line symbol was sent, thus recovering the original bit
Because only a known set of line symbols are sent, and nothing in between,
the receiver can assume that the intended line symbol is that one that is
closest to one of these known line symbols.
Design of such symbol sets is a career, and there is a large literature, but
a good place to start is any college textbook on data communications.
The difference between digital and analog is one is digital, the
other is analog.
Analog signals are signals af varying frequency and intensity.
You can get a good signal, a weak signal, or a bad signal
Digital signals are a pulse train of ones and zeroes. There is error
checking built in - and you either get a signal or you don't. No such
thing as "fringe reception" If you get the sinal the digital to
analog converters decipher the code, and/or codecs in firmware decode
the signal to audio and video signals,
On Sat, 26 Dec 2015 22:52:47 -0500, email@example.com wrote:
OK, I'm all for tautologies as arguments. ;-)
IOW, DSL, ADTV, Satellite TV, Cell phones, and just about everything
else that's considered "digital". You will get errors, retries, data
drop, freezes, and all that jazz before it drops the connection
OK, so the question remains, is v.90 digital or analog?
Your "distinction" isn't, either.
As something of an "expert", I say that if the data is abstractable to a
sequence of 0's and 1's,
then even if it is transmitted in an analog fashion, then it's
*digital*. E.g. Computer files are digital. A paper tape is digital.
While, not an expert about them, I would say that a cassette recording
is not digital.
Not really... Except we didn't have hard drives in those days. If we had
diskette drives we were doing good. (Everyone seemed to have the 1541 if
they had a Commodore 64, though.)
I've always wondered if we'd be successful playing an old computer's
cassette "recording" over the phone line to another computer that was
listening for it. Basically, convert the cassette ports in to a modem. I
know it's an extremely convoluted and pathetic way to do it, but sometimes
that's reason enough to do it!
It's been tried. It kinda half works - but 99%accuracy in digital
communication without error correction is virtually useless - and the
best results were well jnder 99%. (If I remember correctly we achieved
better than 80% -)so we went to "plan b" with the Telex tape
duplicator and "sneakernet" to distribute the programs.
Actually in the late 70's early 80's I ordered parts from GM/GMPD using
a thermal heat print terminal/computer terminal. With a keyboard and a
dual cassette deck on top I would communicate with our inventory control
service provider, Reynolds and Reynolds. I would run a routine from
that terminal to generate a stock order, get the results, and record
them on a cassette, they looked like the common cassette. From there I
flipped a series of toggle switches and typed in a phone number to
GMPD's computer and their computer communicated with my terminal and
read the cassette. The response of their computer was sent back and
recorded on the other cassette on my terminal. And finally my terminal
read the cassette and answer from GMPD and printed the results on that
terminals thermal heat print paper.
The Reynolds and Reynolds and ADP systems used modems to send and
recieve the data - which implemented error checking and correction.
A lot of those early modems used "accoustic couplers" - you placed the
handset of the phone onto the coupler and it "talked" to the phone to
transmit the modulated signals. I think that worked all the way up to
about 200 baud. - mabee 300.
That was about the limit for data transmission on the audio tape too.
Even then I thought the R&R service was archaic. A few years later we
switched to ADP and it was like we switched to the current century. Then
we built a new facility and had ADP in house. I loved that system.
The R&R mentioned above terminal was. TI. When we opened that dealership I
had to temporarily use the handset coupler, the regular modem had not yet
arrived. IIRC one or the other accomplished 300.
On Sun, 27 Dec 2015 19:21:18 +0000 (UTC), Larry Blanchard
Actually both speed and capacity went UP. The first 5.25 disks I
used were somethink like 80kb Shugart hard sectored, then 360kb soft
sectored, then up to DSDD 1.2mb.
The 3.5" disks started at 280 (which never went anywhere) then 360
single sided, 720 double sided, and 1.44mb DSDD (or HD).
Then came the Flopticals, LS120 and LS240 3.5 disks with 21, 120, and
240MB capacity.and a few other nonstandard (Proprietary) systems that
were ineffective to varying degrees.
Flopticals were nice at the time. I still have a final-generation
floptical USB drive that gets used occasionally when someone needes to
read a 3-1/2 inch diskette. One neat trick was that with the right
driver they could get something like 16 meg on a standard diskette.
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