Greetings -
Just to let you know, at $20 for 6 questions, I've allocated time as
needed for a $3.33/question price point. I think this is fair and
consistent with our terms of service. I hope this is sufficient for
what you require. You may consider posting each question separately
at a higher price point if you require more information. If you need
additional clarification/info on these below, please let me know
before rating this answer. Thanks -- jbf777-ga.
A public library
--------------------
As noted in your example, a public library may use any make and model
of a typical barcode scanner, such as the ones found at
http://www.idrecall.com/scanners.htm . This is by far the most
pervasive method used today. These items work by interfacing into a
typical IBM-compatible PC/computer, which is networked into the rest
of the library's terminals; these terminals in turn may be networked
to additional offsite terminals. Today's scanners have intelligent
software built into them, and they can interface into a library's
computers in a variety of fashions, such as via USB or PS2 ports. A
company such as ID Recall Systems [see aforementioned web site] will
typically consult with a library to assess it's software setup in
order to pre-program the scanners to interface with them. The
methodology by which the data is stored is unique to each library's
setup and software, as there are a number of library software
applications for storing library book/media data. Common to each is
the storage of information for each piece of media in a database
record, such as a book's identification decimal, rental status,
renter's info, etc.
A Supermarket
---------------------
The "UPC" is the standard for retail grocery stores, adopted in the
1970's. Similar to the library example above, bar codes on food
products have a unique "product number" embedded in it. When read by
a bar code reader and transmitted to the computer -- with software
which again can vary from store to store -- the computer finds the
item record(s) associated with that item number. These records contain
price, vendor name, quantity on-hand, description, etc. The
computer/software looks up the price by reading the bar code, and then
it creates a register of the items and adds the price to the subtotal
of the groceries purchased. I'm unable to supply direct images with
this answer, but I can point you to some images on the web. See:
http://www.barcodehq.com/primer.html for a primer on bar codes along
with descriptive pictures. Additional information and pictures on
supermarket-specific codes can be seen at
http://www.checkout-systems.com/pages/english/indexframe.html. Here's
a picture of a typical supermarket barcode reader:
http://www.phihong.com/html/barcode_scanners_and_printers.html.
Here's a company that sells all sorts of supermarket scanning
equipment. http://www.lbsonline.freeserve.co.uk/
Factors to consider when buying a printer
--------------------------------------------------------
Three types of printers commonly used with associated typical print
resolution and output speed:
inkjet:
720 x 720 DPI to 2400 x 1200 DPI, although 600-1200 is becoming more
mainstream 8-21 pages per minute.
laser:
600 DPI is popular, but 1200+ is more and more frequent. 10-15 Pages
per minute is common.
dye sub:
600x300 -- 1-5 pages per minute.
There are numerous factors to consider when buying a printer. Firstly
is budget. Are you in the $100-$200 range, or the $1000+ range?
Second, do you need color capability, or are you mostly going to be
printing black and white text with the occasional black and white
photo? Today's inkjets can be very cheap in the color department, but
still don't quite offer the crystal clear text printing of a laser.
Thirdly is speed. Do you want to be waiting around for each page to
print, or do you need really quick output? All these factors will
influence the price.
LCD advantages over CRT
------------------------------------
LCD [liquid-crystal display] is a newer, evolving technology that
incorporates both space and energy saving characteristics. The most
quickly noticeable advantage of LCD over CRT [traditional cathode ray
tube] is space conservation. A typical LCD, flat-panel monitor can
take up 1/3 the space of a typical CRT monitor. Up until more
recently, CRT screens were typically bigger, but this is changing
rapidly, as newer, cheaper technology is affording manufacturers the
ability to create comparable sizes. CRT monitors traditionally had
the edge in the ability to display unlimited colors, but this too is
changing, as newer LCD panels are displaying unlimited colors as well.
LCD panels are also much lighter, as there is physically a lot less
electronics necessary to function.
Backing storage devices: factors to consider
-------------------------------------------------------------
In any multi-user environment, such a library or supermarket, where
potentially many librarians or store clerks are accessing the same
database, reliable multi-user enabled storage devices are imperative.
Regular, stock hard drives many not suffice in this application, as
they are not made to withstand the industrial-level load of a large
network, which could be found in a library or supermaerket. Instead,
a library may opt for a RAID-based (Redundant Array of Independent
Disks) setup, where redundant data is stored in a more
multi-user-conducive configuration. The redundancy element can afford
the real-time protection of sensitive data. In addition, such
industrial applications normally employ additional backup units, in
the form of tape, CD, DVD, or any of a number of available formats,
which will often provide scheduled backups of data. Choosing what
hard drives and backup data to use largely depends on the individual
company's needs and budget. Target questions may include, "how much
space do we need?" "are their volume discounts on many drives?"
"what backup medium provides the best speed-cost-space-reliability
ratios?"
Main differences between CD-ROM and Magnetic disk storage
-------------------------------------------------------------------------------------
Magnetic disk storage, such as a "hard disk" have a hard platter that
holds the magnetic media. Both hard disks and cassette tapes share
the same magnetic recording techniques. Ferromagnetic material is
exposed to a magnetic field which permanently magnetizes it.
Information on a hard disk is easily eraseable and rewritten by
"remembering" these magnetic flux patterns impressed upon the disk.
The fundmental technology here is magnetic in nature, as opposed to
optical/laser technology found in a CD-ROM reader/writer. Here, to
read data, a laser passes through a polycarbonate layer on the disk,
reflecting off the aluminmum layer, hitting an opto-electronic device
that detects light changes. Each difference in reflectivity is
measured and translated into data. To write data, a layer of dye is
heated with a specific concentration of light at a paritcular
frequency which turns the dye opaque. This darkened point is
unpassable by the light. By selectively darkening various areas, a CD
burner creates digital 0's and 1's -- patterns of binary numbers
representative of the stored data, which can be read by the
aforementioned process. The fundmantal difference between the CD and
magnetic technology is use of laser in the former, and magnet in the
latter. See
Sources:
http://www.howstuffworks.com/cd2.htm
http://www.howstuffworks.com/cd-burner2.htm
http://faculty.nnmcc.edu/Jamestadlock/Chapter5.htm
http://www.touchscreens.com/intro-displaytech.html
http://www.barcodehq.com/primer.html
Search Terms:
barcode library scanning
supermarket barcode readers
raid
Additional links:
http://www.kodak.com/global/en/professional/products/storage/pcd/techInfo/permanence6.jhtml
for information about CD-ROM writing. |
