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Please explain the differences between ports; parallel? usb? serial?  

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I was wondering about the performance differences. Someone said that
using USB for a scanner for high resolution would be slower than a
parallel port.  Anyone have info on that one?

Now to answer your question:

Parallel port means there are multiple wires on the cable all carrying
part of the data.  The parallel port on printers has 8 data wires and
several more for control.  Therefore a whole byte can be sent at once.

Serial ports, mean all the bits are sent in sequence.  The orginal PC's
had 25 pin connectors; all new PCs have 9 pin connectors.  In practice
all the data is carried on 1 wire out and a different wire back.  For
example, not that long ago modems were all external and had rates of
1200 or 9600 bits per second.  There were some extra bits for the start
and stop of each byte, so in practice the data is sent at a rate of 120 or
960 bytes per second.  With serial ports, it is absolutely necessary to
have things set up for the correct bit rate.

USB is a rather new style serial bus.  It is being supported by many
manufacturers for many products.  It is also designed to allow one to
connect or disconnect devices while the computer is turned on.  

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Quote:>> Please explain the differences between ports; parallel? usb? serial?
>I was wondering about the performance differences. Someone said that
>using USB for a scanner for high resolution would be slower than a
>parallel port.  Anyone have info on that one?

>Now to answer your question:

>Parallel port means there are multiple wires on the cable all carrying
>part of the data.  The parallel port on printers has 8 data wires and
>several more for control.  Therefore a whole byte can be sent at once.

There are several aspects you forgot to mention:
data speed and wiring constraints.

[http://www6.tomshardware.com/ has a wonderful overview of this
but so help me, I can't find it now particularly with the search broken.
He had a nice table of ports vs max speeds and why]

PC parallel ports were originally intended just for printers,
so they were output only and only status input (paper out, busy, etc).
By using 9 wires for data at a speed of about
1 MHz (1,000,000 cycles per second),
you got speeds of 1 MegaBYTE per second.
Then bidirectional ports were available, and then higher speed
so with the new ECP/EPP (I keep forgetting which is which)
you can achieve about 2-3 MegaBYTES per second for a few devices.
Since there are only 9 data wires, data can go either IN or OUT
but not BOTH at the same time.

Doe to electrical considerations, the wire may only be about
10 feet in length.  Some parallel port devices (such as ZIP drives)
have "pass through" connectors
to allow multiple devices on the same parallel port.

You can usually have 2-3 parallel ports on one PC directly,
but you can have more via the USB (there are converter/adapters).

Quote:>Serial ports, mean all the bits are sent in sequence.  The orginal PC's
>had 25 pin connectors; all new PCs have 9 pin connectors.  In practice
>all the data is carried on 1 wire out and a different wire back.

Serial ports using the RS232 standard have been around a LONG time
so they're terrific for connecting to older "legacy" hardware.
Data is sent ONE bit at a time on the XMT wire,
received one BIT at a time on the RCV wire.
"full duplex" devices can transmit and receive simultaneously.
Currently, speeds up to 115,200 BITS per second are supported,
which is 11,520 BYTES per second IN EACH DIRECTION
(divide by 10, not 8 due to timing signals around the data).
Going faster is possible if using external clocks and symchronous mode
a-la IBM's SDLC instead of asymchronous.
Apple pushed the serial chips to 1 megaBIT for AppleTalk!)

Serial lines can be run really long (hundread of feet) if using
proper cables, and can be extended for miles by using
"short haul modems" which boost the signal.
Regular modems extend their reach too!

Typically, serial lines are point to point
(ex: just a MOUSE on the port, just one printer on the port, etc).
While it is *possible* to have >1 device on one serial port
(ex: a terminal with a pass-thru printer port),
that's getting rare now that ports are not so expensive.

Quote:>USB is a rather new style serial bus.  It is being supported by many
>manufacturers for many products.  It is also designed to allow one to
>connect or disconnect devices while the computer is turned on.

http://www.usb.org/ is an authoritative source.

USB is a 12 megaBIT (thus 1.5 MegaBYTE/second) speed serial interface
that's more like a network since it also implies a protocol
to allow multiple devices sharing the same wire.
Devices self identify thus being Plug-and-play.

USB is REALLY popular now since it simplifies wiring.
It's now on the Macs as well as PC,
but it's mostly supported by WIndows-98.
You can have kybd, mouse, printer, scanner, etc all on ONE wire
(well, via hubs and pass-thru connectors: you can't just just
tap into the wire like the old coax ethernets).
BUT beware the wire limitations of about 6 feet and 2 hub cascade limit!
If you want to reach further, consider wireless
or a real network such as ethernet or 10/100-base-t.

quick simmary:
serial: 11k BYTES/second speed, one device per port
parallel: 1-3 MegaBYTES/second speed, sometimes >1 device per port
USB: 12 megaBIT/second (1.5 megaByet/sec), shared among devices
ethernet: 10 or 100 megaBIT/second, highly shared among devices
--
Jeffrey Jonas

The original Dr. JCL and Mr .hide

FYI, you can do the same thing with serial or parallel ports,
even though they weren't (?!) designed for that.  

Parallel:  device is capable of receiving several bits at a time.
USB:  Universal Serial Bus is an external bus standard that supports up to
12Mbps and a USB port can support up to 127 devices.
Serial:  Opposite of parallel.. transferring only one bit at a time.

USB is the latest of those hence the best.

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You want the physical description, capabilities, usage, or what? They are
physically different ports...

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Hot connects are permitted under the RS-232 serial port standard
and shouldn't cause damage "in a properly engineered RS-232
interface". Not so for regular parallel ports.

what utter *is that? USB is the newest and therefore the best? what the
hell are you thinking. i have win98 SE. it crashes almost every time i shut
down. good old DOS however, crashed on me twice in my 6 years of using it. so
which is better?Netscape 4.7 crashes left and right, but it is newer than lynx,
which is rock solid and doesnt crash for me, so i guess netscape is better
right?I have a really old IBM keyboard, the ~5 pounder with a pleasing "clack"
every time i press a key. i love that keyboard. i also have a "mouse systems"
win 95 keyboard, which is approximately 15 years newer. even tho the mouse
systems sucks, its gotta be better, cause 15 years, is like, ancient man. dont
be stupid. you cant judge the quality or use of a technology just by its age.i
have a new motherboard, being used by a P3. that motherboard is so firmly
sucking on my left nut, it will never be removed. it is a piece of crap,
onboard everything, evertything crappy, no expansion capabilities. i also have
an old motherboard, an LX which is being used by a P2 which i am typing this
on. it rules. it has lots of expansion slots, a good layout, etc. just because
its older doesnt mean its worse. it just depends on the quality of the
manufacturer.
eli
oh, and btw, your data is flawed. in THEORY, usb can handle 127 devices, but
because of power, i think it can only support ~36

Quote:>Parallel:  device is capable of receiving several bits at a time.
>USB:  Universal Serial Bus is an external bus standard that supports up to
>12Mbps and a USB port can support up to 127 devices.
>Serial:  Opposite of parallel.. transferring only one bit at a time.

>USB is the latest of those hence the best.

I have done many hot connects on RS-232 and parallel and never
had any problem.  Doing the same with the mouse (PS/2), keyboard,
or HD controller (MFM/IDE/SCSI) cables almost always led to
lockup or reboot.   I'm not surprised on the HD cables, but
hot plugging rodents or claviatures should not disrupt the PC,
IMHO.

9 for data?!?  

Quote:> Since there are only 9 data wires, data can go either IN or OUT
> but not BOTH at the same time.
> Currently, speeds up to 115,200 BITS per second are supported,
> which is 11,520 BYTES per second IN EACH DIRECTION

The exact number really depends of the format.  8,N,1 will give
you more than 7,E,1, for instance.

[parallel ports use]

Quote:>> By using 9 wires for data at a speed of about
>9 for data?!?

8 data + parity to be precise.
I can't remember if the parallel chip generates & checks the
parity or just passes that thru, thus allowing a 9th data bit
if you wanna risk no parity checking.

[serial speed calculations]

Quote:>> Currently, speeds up to 115,200 BITS per second are supported,
>> which is 11,520 BYTES per second IN EACH DIRECTION
>The exact number really depends of the format.  8,N,1 will give
>you more than 7,E,1, for instance.

Huh?
8.N.1 means 8 data bits, no parity, 1 stop bit
        for a total of 9 bits + start bit = 10 bits
7.E.1 means 7 data bits, EVEN parity, 1 stop bit
        for a total of 9 bits + start bit = 10 bits
That seems the same to me!

Had you said 7.N.1 I'd agree that it's faster to handle 7 bits
than 8 bits, but few things use 7 bits these days.
--
Jeffrey Jonas

The original Dr. JCL and Mr .hide

I mean, in the first case you get 8 usable bits (a byte)
out of 10 bits, in the latter, you get only 7 bits out
of 10, dropping the effective throughput somewhat.

I should've made my examples 8,N,1 and 8,E,1 to make
this clearer.

Quote:> Had you said 7.N.1 I'd agree that it's faster to handle 7 bits
> than 8 bits, but few things use 7 bits these days.