Search The World
Custom Search
Monday, August 18, 2008
Saturday, August 16, 2008
Partial lunar eclipse coming Aug. 16
Eclipses of the sun and moon usually come in pairs. A solar eclipse is almost always accompanied by a lunar eclipse two weeks before or after it, since in two weeks the moon travels halfway around its orbit and is likely to form another almost-straight line with the Earth and sun.
This month will be no exception. Just over two weeks after casting its shadow across the Arctic, Russia, Mongolia and China, the moon will swing around to slide deep through the northern edge of the Earth's own shadow on the night of Aug. 16-17.
This partial lunar eclipse will favor much of Europe, Africa and Asia. The moon will pass through the northern part of the Earth's dark umbral shadow between 3:36 p.m. and 6:44 p.m. EDT (19:36 and 22:44 GMT) on Aug. 16.
source :http://www.msnbc.msn.com/id/26225047/
This month will be no exception. Just over two weeks after casting its shadow across the Arctic, Russia, Mongolia and China, the moon will swing around to slide deep through the northern edge of the Earth's own shadow on the night of Aug. 16-17.
This partial lunar eclipse will favor much of Europe, Africa and Asia. The moon will pass through the northern part of the Earth's dark umbral shadow between 3:36 p.m. and 6:44 p.m. EDT (19:36 and 22:44 GMT) on Aug. 16.
source :http://www.msnbc.msn.com/id/26225047/
Monday, July 21, 2008
This is What Bill Gates said
Bill Gates recently gave a speech at a High School
about 11 things they did not and will not learn in school
. He talks about how feel-good, politically correct teachings created a generation of kids with no concept of reality and how this concept set them up for failure in the real world.
Rule 1
: Life is not fair - get used to it!
Rule 2
: The world won't care about your self-esteem. The world will expect you to accomplish something BEFORE you feel good about yourself.
Rule 3
: You will NOT make $60,000 a year right out of high school. You won't be a vice-president with a car phone until you earn both.
Rule 4
: If you think your teacher is tough, wait till you get a boss.
Rule 5
: Flipping burgers is not beneath your dignity. Your Grandparents had a different word for burger flipping: they called it opportunity.
Rule 6
: If you mess up, it's not your parents' fault, so don't whine about your mistakes, learn from them.
Rule 7
: Before you were born, your parents weren't as boring as they are now. They got that way from paying your bills, cleaning your clothes and listening to you talk about how cool you thought you were. So before you save the rain forest from the parasites of your parent's generation, try delousing the closet in your own room.
Rule 8
: Your school may have done away with winners and losers, but life HAS NOT. In some schools, they have abolished failing grades and they'll give you as MANY TIMES as you want to get the right answer. This doesn't bear the slightest resemblance to ANYTHING in real life.
Rule 9
: Life is not divided into semesters. You don't get summers off and very few employers are interested in helping you FIND YOURSELF. Do that on your own time.
Rule 10
: Television is NOT real life. In real life people actually have to leave the coffee shop and go to jobs.
Rule 11
: Be nice to nerds. Chances are you'll end up working for one.
about 11 things they did not and will not learn in school
. He talks about how feel-good, politically correct teachings created a generation of kids with no concept of reality and how this concept set them up for failure in the real world.
Rule 1
: Life is not fair - get used to it!
Rule 2
: The world won't care about your self-esteem. The world will expect you to accomplish something BEFORE you feel good about yourself.
Rule 3
: You will NOT make $60,000 a year right out of high school. You won't be a vice-president with a car phone until you earn both.
Rule 4
: If you think your teacher is tough, wait till you get a boss.
Rule 5
: Flipping burgers is not beneath your dignity. Your Grandparents had a different word for burger flipping: they called it opportunity.
Rule 6
: If you mess up, it's not your parents' fault, so don't whine about your mistakes, learn from them.
Rule 7
: Before you were born, your parents weren't as boring as they are now. They got that way from paying your bills, cleaning your clothes and listening to you talk about how cool you thought you were. So before you save the rain forest from the parasites of your parent's generation, try delousing the closet in your own room.
Rule 8
: Your school may have done away with winners and losers, but life HAS NOT. In some schools, they have abolished failing grades and they'll give you as MANY TIMES as you want to get the right answer. This doesn't bear the slightest resemblance to ANYTHING in real life.
Rule 9
: Life is not divided into semesters. You don't get summers off and very few employers are interested in helping you FIND YOURSELF. Do that on your own time.
Rule 10
: Television is NOT real life. In real life people actually have to leave the coffee shop and go to jobs.
Rule 11
: Be nice to nerds. Chances are you'll end up working for one.
Saturday, July 19, 2008
Monday, July 7, 2008
Mouse Events
We’ll go through all mouse events: mousedown, mouseup and click, dblclick, mousemove and finally mouseover and mouseout. Then I explain the relatedTarget, fromElement and toElement event properties. Finally the Microsoft proprietary mouseenter and mouseleave events.
For browser compatibility, see the Event Compatibility Tables page.
Example
Here’s a small example. Try it to better understand the explanations below.
Mousedown, mouseup, click and dblclick are registered to the link. You’ll see the events that take place in the textarea, or in an alert, if you so choose.
The event handlers are registered on this link.
Clear textarea.
Show alert instead of writing to textarea
Mousedown, mouseup, click
If the user clicks on an element no less than three mouse events fire, in this order:
1. mousedown, user depresses the mouse button on this element
2. mouseup, user releases the mouse button on this element
3. click, one mousedown and one mouseup detected on this element
In general mousedown and mouseup are more useful than click. Some browsers don’t allow you to read out mouse button information onclick. Furthermore, sometimes the user does something with his mouse but no click event follows.
Suppose the user depresses the mouse button on a link, then moves his mouse off the link and then releases the mouse button. Now the link only registers a mousedown event. Similarly, if the user depresses the mouse button, then moves the mouse over a link and then releases the mouse button, the link only registers a mouseup. In neither case does a click event fire.
Whether or not this is a problem depends on the user interaction you want. But you should generally register your script onmousedown/up, unless you’re completely sure you want the click event and nothing else.
If you use alerts in handling these events, the browser may lose track of which event took place on which element and how many times it took place, messing up your scripts. So it’s best not to use alerts.
Dblclick
The dblclick event is rarely used. Even when you use it, you should be sure never to register both an onclick and an ondblclick event handler on the same HTML element. Finding out what the user has actually done is nearly impossible if you register both.
After all, when the user double–clicks on an element one click event takes place before the dblclick. Besides, in Netscape the second click event is also separately handled before the dblclick. Finally, alerts are dangerous here, too.
So keep your clicks and dblclicks well separated to avoid complications.
Mousemove
The mousemove event works fine, but you should be aware that it may take quite some system time to process all mousemove events. If the user moves the mouse one pixel, the mousemove event fires. Even when nothing actually happens, long and complicated functions take time and this may affect the usability of the site: everything goes very slowly, especially on old computers.
Therefore it’s best to register an onmousemove event handler only when you need it and to remove it as soon as it’s not needed any more:
element.onmousemove = doSomething;
// later
element.onmousemove = null;
Mouseover and mouseout
Take another look at the example, switch the mouseovers on and try them. The example adds an onmouseover event handler to ev3 only. However, you’ll notice that a mouseover event takes place not only when the mouse enters ev3's area, but also when it enters the area of ev4 or the span. In Mozilla before 1.3, the event even fires when the mouse enters the area of a text!
The reason for this is of course event bubbling. The user causes a mouseover event on ev4. There is no onmouseover event handler on this element, but there is one on ev3. As soon as the event has bubbled up to this element, the event handler is executed.
Now this setup, though completely correct, gives us some problems. Our first problem is targeting. Suppose the mouse enters ev4:
-----------------------------------------
| This is div id="ev3" |
| ----------------------------- |
| | This is div id="ev4" | |
| | -------- <-------- |
| | | span | | |
| | | | | |
| | -------- | |
| ----------------------------- |
-----------------------------------------
<--------: mouse movement
Now the target/srcElement of this event is ev4: it’s the element the event took place on, since the user mouses over it. But when this happens:
-----------------------------------------
| This is div id="ev3" |
| ----------------------------- |
| | This is div id="ev4" | |
| | -------- | |
| | | span | | |
| | | --------> | |
| | -------- | |
| ----------------------------- |
-----------------------------------------
-------->: mouse movement
the event has exactly the same target/srcElement. Here, too, the mouse enters ev4. Nonetheless you might want do one thing when the mouse comes from ev3 and another thing when it comes from the SPAN. So we need to know where the mouse comes from.
relatedTarget, fromElement, toElement
W3C added the relatedTarget property to mouseover and mouseout events. This contains the element the mouse came from in case of mouseover, or the element it goes to in case of mouseout.
Microsoft created two properties to contain this information:
* fromElement refers to the element the mouse comes from. This is interesting to know in case of mouseover.
* toElement refers to the element the mouse goes to. This is interesting to know in case of mouseout.
In our first example, relatedTarget/fromElement contains a reference to ev4, in our second example to the SPAN. Now you know where the mouse came from.
Cross–browser scripts
So if you want to know where the mouse comes from in case of mouseover, do:
function doSomething(e) {
if (!e) var e = window.event;
var relTarg = e.relatedTarget || e.fromElement;
}
If you want to know where the mouse goes to in case of mouseout, do:
function doSomething(e) {
if (!e) var e = window.event;
var relTarg = e.relatedTarget || e.toElement;
}
Mousing out of a layer
In a layer-based navigation you may need to know when the mouse leaves a layer so that it can be closed. Therefore you register an onmouseout event handler to the layer. However, event bubbling causes this event handler to fire when the mouse leaves any element inside the layer, too.
--------------
| Layer |.onmouseout = doSomething;
| -------- |
| | Link | ----> We want to know about this mouseout
| | | |
| -------- |
| -------- |
| | Link | |
| | ----> | but not about this one
| -------- |
--------------
---->: mouse movement
Another show stopper is that when you move the mouse into the layer, and then onto a link, browsers register a mouseout event on the layer! It doesn't make much sense to me (the mouse is still in the layer), but all browsers agree on this one.
So how do we reject any mouseout that does not take place when the mouse actually leaves the layer?
function doSomething(e) {
if (!e) var e = window.event;
var tg = (window.event) ? e.srcElement : e.target;
if (tg.nodeName != 'DIV') return;
var reltg = (e.relatedTarget) ? e.relatedTarget : e.toElement;
while (reltg != tg && reltg.nodeName != 'BODY')
reltg= reltg.parentNode
if (reltg== tg) return;
// Mouseout took place when mouse actually left layer
// Handle event
}
First get the event target, ie. the element the mouse moved out of. If the target is not the DIV (layer), end the function immediately, since the mouse has certainly not left the layer.
If the target is the layer, we're still not sure if the mouse left the layer or entered a link within the layer. Therefore we're going to check the relatedTarget/toElement of the event, ie. the element the mouse moved to.
We read out this element, and then we're going to move upwards through the DOM tree until we either encounter the target of the event (ie. the DIV), or the body element.
If we encounter the target the mouse moves towards a child element of the layer, so the mouse has not actually left the layer. We stop the function.
When the function has survived all these checks we're certain that the mouse has actually left the layer and we can take appropriate action (usually making the layer invisible).
Mouseenter and mouseleave
Microsoft has another solution. It has created two new events mouseenter and mouseleave. They are almost the same as mouseover and mouseout except that they don’t react to event bubbling. Therefore they see the entire HTML element they’re registered to as one solid block and don’t react to mouseovers and –outs taking place inside the block.
So using these events solves our problem too: they react only to mouseovers/outs on the element they’re registered to.
At the moment these events are only supported by Explorer 5.5 on Windows and higher. Maybe the other browser vendors will copy these events.
End
You have now reached the end of my Introduction to Events. Good luck in writing your own event handling scripts.
source:: http://www.quirksmode.org/js/events_mouse.html
For browser compatibility, see the Event Compatibility Tables page.
Example
Here’s a small example. Try it to better understand the explanations below.
Mousedown, mouseup, click and dblclick are registered to the link. You’ll see the events that take place in the textarea, or in an alert, if you so choose.
The event handlers are registered on this link.
Clear textarea.
Show alert instead of writing to textarea
Mousedown, mouseup, click
If the user clicks on an element no less than three mouse events fire, in this order:
1. mousedown, user depresses the mouse button on this element
2. mouseup, user releases the mouse button on this element
3. click, one mousedown and one mouseup detected on this element
In general mousedown and mouseup are more useful than click. Some browsers don’t allow you to read out mouse button information onclick. Furthermore, sometimes the user does something with his mouse but no click event follows.
Suppose the user depresses the mouse button on a link, then moves his mouse off the link and then releases the mouse button. Now the link only registers a mousedown event. Similarly, if the user depresses the mouse button, then moves the mouse over a link and then releases the mouse button, the link only registers a mouseup. In neither case does a click event fire.
Whether or not this is a problem depends on the user interaction you want. But you should generally register your script onmousedown/up, unless you’re completely sure you want the click event and nothing else.
If you use alerts in handling these events, the browser may lose track of which event took place on which element and how many times it took place, messing up your scripts. So it’s best not to use alerts.
Dblclick
The dblclick event is rarely used. Even when you use it, you should be sure never to register both an onclick and an ondblclick event handler on the same HTML element. Finding out what the user has actually done is nearly impossible if you register both.
After all, when the user double–clicks on an element one click event takes place before the dblclick. Besides, in Netscape the second click event is also separately handled before the dblclick. Finally, alerts are dangerous here, too.
So keep your clicks and dblclicks well separated to avoid complications.
Mousemove
The mousemove event works fine, but you should be aware that it may take quite some system time to process all mousemove events. If the user moves the mouse one pixel, the mousemove event fires. Even when nothing actually happens, long and complicated functions take time and this may affect the usability of the site: everything goes very slowly, especially on old computers.
Therefore it’s best to register an onmousemove event handler only when you need it and to remove it as soon as it’s not needed any more:
element.onmousemove = doSomething;
// later
element.onmousemove = null;
Mouseover and mouseout
Take another look at the example, switch the mouseovers on and try them. The example adds an onmouseover event handler to ev3 only. However, you’ll notice that a mouseover event takes place not only when the mouse enters ev3's area, but also when it enters the area of ev4 or the span. In Mozilla before 1.3, the event even fires when the mouse enters the area of a text!
The reason for this is of course event bubbling. The user causes a mouseover event on ev4. There is no onmouseover event handler on this element, but there is one on ev3. As soon as the event has bubbled up to this element, the event handler is executed.
Now this setup, though completely correct, gives us some problems. Our first problem is targeting. Suppose the mouse enters ev4:
-----------------------------------------
| This is div id="ev3" |
| ----------------------------- |
| | This is div id="ev4" | |
| | -------- <-------- |
| | | span | | |
| | | | | |
| | -------- | |
| ----------------------------- |
-----------------------------------------
<--------: mouse movement
Now the target/srcElement of this event is ev4: it’s the element the event took place on, since the user mouses over it. But when this happens:
-----------------------------------------
| This is div id="ev3" |
| ----------------------------- |
| | This is div id="ev4" | |
| | -------- | |
| | | span | | |
| | | --------> | |
| | -------- | |
| ----------------------------- |
-----------------------------------------
-------->: mouse movement
the event has exactly the same target/srcElement. Here, too, the mouse enters ev4. Nonetheless you might want do one thing when the mouse comes from ev3 and another thing when it comes from the SPAN. So we need to know where the mouse comes from.
relatedTarget, fromElement, toElement
W3C added the relatedTarget property to mouseover and mouseout events. This contains the element the mouse came from in case of mouseover, or the element it goes to in case of mouseout.
Microsoft created two properties to contain this information:
* fromElement refers to the element the mouse comes from. This is interesting to know in case of mouseover.
* toElement refers to the element the mouse goes to. This is interesting to know in case of mouseout.
In our first example, relatedTarget/fromElement contains a reference to ev4, in our second example to the SPAN. Now you know where the mouse came from.
Cross–browser scripts
So if you want to know where the mouse comes from in case of mouseover, do:
function doSomething(e) {
if (!e) var e = window.event;
var relTarg = e.relatedTarget || e.fromElement;
}
If you want to know where the mouse goes to in case of mouseout, do:
function doSomething(e) {
if (!e) var e = window.event;
var relTarg = e.relatedTarget || e.toElement;
}
Mousing out of a layer
In a layer-based navigation you may need to know when the mouse leaves a layer so that it can be closed. Therefore you register an onmouseout event handler to the layer. However, event bubbling causes this event handler to fire when the mouse leaves any element inside the layer, too.
--------------
| Layer |.onmouseout = doSomething;
| -------- |
| | Link | ----> We want to know about this mouseout
| | | |
| -------- |
| -------- |
| | Link | |
| | ----> | but not about this one
| -------- |
--------------
---->: mouse movement
Another show stopper is that when you move the mouse into the layer, and then onto a link, browsers register a mouseout event on the layer! It doesn't make much sense to me (the mouse is still in the layer), but all browsers agree on this one.
So how do we reject any mouseout that does not take place when the mouse actually leaves the layer?
function doSomething(e) {
if (!e) var e = window.event;
var tg = (window.event) ? e.srcElement : e.target;
if (tg.nodeName != 'DIV') return;
var reltg = (e.relatedTarget) ? e.relatedTarget : e.toElement;
while (reltg != tg && reltg.nodeName != 'BODY')
reltg= reltg.parentNode
if (reltg== tg) return;
// Mouseout took place when mouse actually left layer
// Handle event
}
First get the event target, ie. the element the mouse moved out of. If the target is not the DIV (layer), end the function immediately, since the mouse has certainly not left the layer.
If the target is the layer, we're still not sure if the mouse left the layer or entered a link within the layer. Therefore we're going to check the relatedTarget/toElement of the event, ie. the element the mouse moved to.
We read out this element, and then we're going to move upwards through the DOM tree until we either encounter the target of the event (ie. the DIV), or the body element.
If we encounter the target the mouse moves towards a child element of the layer, so the mouse has not actually left the layer. We stop the function.
When the function has survived all these checks we're certain that the mouse has actually left the layer and we can take appropriate action (usually making the layer invisible).
Mouseenter and mouseleave
Microsoft has another solution. It has created two new events mouseenter and mouseleave. They are almost the same as mouseover and mouseout except that they don’t react to event bubbling. Therefore they see the entire HTML element they’re registered to as one solid block and don’t react to mouseovers and –outs taking place inside the block.
So using these events solves our problem too: they react only to mouseovers/outs on the element they’re registered to.
At the moment these events are only supported by Explorer 5.5 on Windows and higher. Maybe the other browser vendors will copy these events.
End
You have now reached the end of my Introduction to Events. Good luck in writing your own event handling scripts.
source:: http://www.quirksmode.org/js/events_mouse.html
Wednesday, June 18, 2008
History of Mobile Telephone
History of Mobile Telephone
AT A GLANCE:
Today's communications industry would not be what it is without the contributions made by Richard H. Frenkiel and Joel S. Engel. The big breakthrough came when AT&T Labs researchers Frenkiel and Engel divided wireless communications into a series of cells, then automatically switched callers as they moved so that each cell could be reused. This led to the development of cellular phones and made today’s mobile communications possible.
Invention: mobile telephone
Function: noun / mo·bile tele·phone
Definition: A mobile radiotelephone, often in an automobile, that uses a network of short-range transmitters located in overlapping cells throughout a region, with a central station making connections to regular telephone lines. Also called cellular telephone
Inventor: Joel Engel and Richard Frenkiel
Criteria: First practical cellular telephone system.
Birth: Richard Frenkiel, March 4, 1943 in Brooklyn, New York
Joel Engel, February 4, 1936 in New York City
Nationality: American
Milestones:
1921 The Detroit Police Department, began experimentation with one-way vehicular mobile service.
1928 Detroit Police commenced regular one-way radio communication with all its patrol cars.
1933 Bayonne, NJ Police Department initiated regular two-way communications with its patrol cars
1936 Alton Dickieson, H.I. Romnes and D. Mitchell begin design of AT&T's mobile phone system
1940 Connecticut State Police began statewide two-way, on the frequency modulated (FM)
1941 FM mobile radio became standard throughout the country following the success in Connecticut
1946 A driver in St. Louis, Mo., placed a phone call,it was the first AT&T mobile telephone call.
1948 wireless telephone service was available in almost 100 cities and highway corridors.
1947 cellular telephone service conceived by D.H. Ring at Bell Labs, but the technology didn't exist
1971 Richard Frenkiel and Joel Engel of AT&T applied computers and electronics to make it work.
1973 Martin Cooper of Motorola made the first cellphone call to his rival Joe Engel of AT&T Bell Labs
1978 AT&T conducted FCC-authorized field trials in Chicago and Newark, N.J.
1979 the first cellular network was launched in Japan.
1982 FCC granted commercial licenses to an AT&T subsidiary, Advanced Mobile Phone Service
1983 AMPS was then divided among the local companies as part of the planning for divestiture
1983 Illinois Bell opened the first commercial cellular system in October
CAPs: Joel Engel, Richard Frenkiel, Alton Dickieson, H.I. Romnes, D. Mitchell, D.H. Ring, William (Bill) C. Jakes, Martin Cooper, ARY, mobile phone, mobile telephone, cell phone, cellular phone, cellphone, wireless phone, SIP, history, biography, inventor, invention.
The Story:
Today's communications industry would not be what it is without the contributions made by Richard H. Frenkiel and Joel S. Engel. The big breakthrough came when AT&T Labs researchers Frenkiel and Engel divided wireless communications into a series of cells, then automatically switched callers as they moved so that each cell could be reused. This led to the development of cellular phones and made today’s mobile communications possible.
On June 17, 1946 a driver in St. Louis, Missouri., pulled out a handset from under his car's dashboard, placed a phone call and made history. It was the first mobile telephone call. A team including Alton Dickieson, H.I. Romnesand D. Mitchell from Bell Labs, worked more than a decade to achieve this feat. By 1948, wireless telephone service was available in almost 100 cities and highway corridors. Customers included utilities, truck fleet operators and reporters. However, with only 5,000 customers making 30,000 weekly calls, the service was far from commonplace.
That "primitive" wireless network could not handle large call volumes. A single transmitter on a central tower provided a handful of channels for an entire metropolitan area. Between one and eight receiver towers handled the call return signals. At most, three subscribers could make calls at one time in any city. It was, in effect, a massive party line, where subscribers would have to listen first for someone else on the line before making a call.
Expensive and far from "mobile", the service cost $15 per month, plus 30 to 40 cents per local call, and the equipment weighed 80 pounds. Just as they would use a CB microphone, users depressed a button on the handset to talk and released it to listen.
Improved technology after 1965 brought a few more channels, customer dialing and eliminated the cumbersome handset. But capacity remained so limited that Bell System officials rationed the service to 40,000 subscribers guided by agreements with state regulatory agencies. For example, 2,000 subscribers in New York City shared just 12 channels, and typically waited 30 minutes to place a call. It was wireless, but with "strings" attached.
Something better — cellular telephone service — had been conceived in 1947 by D.H. Ring at Bell Labs, but the idea was not ready for prime time. The system comprised multiple low-power transmitters spread throughout a city in a hexagonal grid, with automatic call handoff from one hexagon to another and reuse of frequencies within a city. The technology to implement it didn't exist, and the frequencies needed were not available. The cellular concept lay barron until the 1960s, when Richard Frenkiel and Joel Engel of Bell Labs applied computers and electronics to make it work.
AT&T turned their work into a proposal to the Federal Communications Commission (FCC) in December 1971. After years of hearings, the FCC approved the overall concept, but licensed two competing systems in each city.
Modern mobile telephony took a giant leap forward on April 3, 1973, when Motorola employee Martin Cooper placed a call to rival AT&T's Bell Labs while walking the streets of New York City talking on the first mobile telephone, a Motorola DynaTAC.
In 1978, AT&T conducted FCC-authorized field trials in Chicago and Newark, N.J. Four years later, the FCC granted commercial licenses to an AT&T subsidiary, Advanced Mobile Phone Service Inc. (AMPS). AMPS was then divided among the local companies as part of the planning for divestiture. Illinois Bell opened the first commercial cellular system in October 1983.
For their pioneering work in cellular telephony, AT&T Labs researchers Richard Frenkiel and Joel Engel earned the National Medal of Technology. Cellular telephony has spawned a Multi-billion dollar industry and has freed tens of millions of people, both at home and at work, to communicate anywhere, any time.
article source:
AT A GLANCE:
Today's communications industry would not be what it is without the contributions made by Richard H. Frenkiel and Joel S. Engel. The big breakthrough came when AT&T Labs researchers Frenkiel and Engel divided wireless communications into a series of cells, then automatically switched callers as they moved so that each cell could be reused. This led to the development of cellular phones and made today’s mobile communications possible.
Invention: mobile telephone
Function: noun / mo·bile tele·phone
Definition: A mobile radiotelephone, often in an automobile, that uses a network of short-range transmitters located in overlapping cells throughout a region, with a central station making connections to regular telephone lines. Also called cellular telephone
Inventor: Joel Engel and Richard Frenkiel
Criteria: First practical cellular telephone system.
Birth: Richard Frenkiel, March 4, 1943 in Brooklyn, New York
Joel Engel, February 4, 1936 in New York City
Nationality: American
Milestones:
1921 The Detroit Police Department, began experimentation with one-way vehicular mobile service.
1928 Detroit Police commenced regular one-way radio communication with all its patrol cars.
1933 Bayonne, NJ Police Department initiated regular two-way communications with its patrol cars
1936 Alton Dickieson, H.I. Romnes and D. Mitchell begin design of AT&T's mobile phone system
1940 Connecticut State Police began statewide two-way, on the frequency modulated (FM)
1941 FM mobile radio became standard throughout the country following the success in Connecticut
1946 A driver in St. Louis, Mo., placed a phone call,it was the first AT&T mobile telephone call.
1948 wireless telephone service was available in almost 100 cities and highway corridors.
1947 cellular telephone service conceived by D.H. Ring at Bell Labs, but the technology didn't exist
1971 Richard Frenkiel and Joel Engel of AT&T applied computers and electronics to make it work.
1973 Martin Cooper of Motorola made the first cellphone call to his rival Joe Engel of AT&T Bell Labs
1978 AT&T conducted FCC-authorized field trials in Chicago and Newark, N.J.
1979 the first cellular network was launched in Japan.
1982 FCC granted commercial licenses to an AT&T subsidiary, Advanced Mobile Phone Service
1983 AMPS was then divided among the local companies as part of the planning for divestiture
1983 Illinois Bell opened the first commercial cellular system in October
CAPs: Joel Engel, Richard Frenkiel, Alton Dickieson, H.I. Romnes, D. Mitchell, D.H. Ring, William (Bill) C. Jakes, Martin Cooper, ARY, mobile phone, mobile telephone, cell phone, cellular phone, cellphone, wireless phone, SIP, history, biography, inventor, invention.
The Story:
Today's communications industry would not be what it is without the contributions made by Richard H. Frenkiel and Joel S. Engel. The big breakthrough came when AT&T Labs researchers Frenkiel and Engel divided wireless communications into a series of cells, then automatically switched callers as they moved so that each cell could be reused. This led to the development of cellular phones and made today’s mobile communications possible.
On June 17, 1946 a driver in St. Louis, Missouri., pulled out a handset from under his car's dashboard, placed a phone call and made history. It was the first mobile telephone call. A team including Alton Dickieson, H.I. Romnesand D. Mitchell from Bell Labs, worked more than a decade to achieve this feat. By 1948, wireless telephone service was available in almost 100 cities and highway corridors. Customers included utilities, truck fleet operators and reporters. However, with only 5,000 customers making 30,000 weekly calls, the service was far from commonplace.
That "primitive" wireless network could not handle large call volumes. A single transmitter on a central tower provided a handful of channels for an entire metropolitan area. Between one and eight receiver towers handled the call return signals. At most, three subscribers could make calls at one time in any city. It was, in effect, a massive party line, where subscribers would have to listen first for someone else on the line before making a call.
Expensive and far from "mobile", the service cost $15 per month, plus 30 to 40 cents per local call, and the equipment weighed 80 pounds. Just as they would use a CB microphone, users depressed a button on the handset to talk and released it to listen.
Improved technology after 1965 brought a few more channels, customer dialing and eliminated the cumbersome handset. But capacity remained so limited that Bell System officials rationed the service to 40,000 subscribers guided by agreements with state regulatory agencies. For example, 2,000 subscribers in New York City shared just 12 channels, and typically waited 30 minutes to place a call. It was wireless, but with "strings" attached.
Something better — cellular telephone service — had been conceived in 1947 by D.H. Ring at Bell Labs, but the idea was not ready for prime time. The system comprised multiple low-power transmitters spread throughout a city in a hexagonal grid, with automatic call handoff from one hexagon to another and reuse of frequencies within a city. The technology to implement it didn't exist, and the frequencies needed were not available. The cellular concept lay barron until the 1960s, when Richard Frenkiel and Joel Engel of Bell Labs applied computers and electronics to make it work.
AT&T turned their work into a proposal to the Federal Communications Commission (FCC) in December 1971. After years of hearings, the FCC approved the overall concept, but licensed two competing systems in each city.
Modern mobile telephony took a giant leap forward on April 3, 1973, when Motorola employee Martin Cooper placed a call to rival AT&T's Bell Labs while walking the streets of New York City talking on the first mobile telephone, a Motorola DynaTAC.
In 1978, AT&T conducted FCC-authorized field trials in Chicago and Newark, N.J. Four years later, the FCC granted commercial licenses to an AT&T subsidiary, Advanced Mobile Phone Service Inc. (AMPS). AMPS was then divided among the local companies as part of the planning for divestiture. Illinois Bell opened the first commercial cellular system in October 1983.
For their pioneering work in cellular telephony, AT&T Labs researchers Richard Frenkiel and Joel Engel earned the National Medal of Technology. Cellular telephony has spawned a Multi-billion dollar industry and has freed tens of millions of people, both at home and at work, to communicate anywhere, any time.
article source:
Sunday, June 15, 2008
Wednesday, April 16, 2008
ZFS or NTFS
Introduction to the two file Systems
Both windows and Solaris allows deletion & creation of files access to files for reading or writing , perform automatic management of secondary memory space and protect files against system failure thus there are many similarities and dissimilarities between the two file systems and they are described in the following article.
ZFS, which doesn't stand for anything. It is just a pseudo-acronym that vaguely suggests a way to store files that gets you a lot of points in Scrabble and is used in Solaris 10. [Jeff Bonwick,2006]
Unlike ZFS, NTFS stands for New Technology File System and is used in Windows XP.
NTFS is designed as a better alternative to FAT 32.
ZFS of Solaris 10 UNIX file Management System
ZFS produced by Sun Micro System and it is an open source file system. Its high capacity and integration of the previously separate concept of file system and volume management in to a single product, novel on disk structure, light weight file system and easy storage pool management. ZFS has 2 main features. ZFS is a 128 bit file system. The report which has been reference to Wikipedia which was referenced in 2006 states the capacity of ZFS as 129 bits; where as in Jeff Bonwick's Blog (who was the project leader of ZFS) states that ZFS is a 128 bit file system. [SunSolaris2008]
ZFS can store 256 quadrillion ZB (1ZB = 1 billion TB or 1 ZB = 270 bytes), which Exceeds quantum limit of Earth-based storage.[opensolaris2006]
Unlike Sun Microsystems, Microsoft who is the developer NTFS is not providing this file system free as it is not an open source file system.
The maximum NTFS volume size as implemented in Windows XP Professional is 232-1 clusters. For example, using 64 KiB clusters, the maximum NTFS volume size is 256 TiB minus 64 KiB [Wikipedia2008]. Compared with ZFS, NTFS can be regarded as having a minute storage capacity.
Windows current file system NTFS can store files up to 4GB in size. Unlike NTFS, ZFS has no theoretical limit for a single file, but the whole file system can be as big as 256 quadrillion ZB as stated above. [Zamwi2007]
When comparing the storage levels of ZFS and NTFS I rather prefer ZFS not only considering its storage levels but also as it is open source.
NTFS of the windows XP file management system
NTFS is used in Windows NT family (Windows NT 3.1 to Windows NT 4.0, Windows 2000, Windows XP, Windows Server 2003, Windows Vista, Windows Server 2008). [wikipedia2008].
NTFS can also be used in Linux with NTFS-3g, Mac OS with Paragon NTFS and ntfs-3g, Mac OS X with NTFS-3g and FreeBSD with NTFS-3g, BeOS with NTFS-3g [wikipedia2008].
ZFS which is the next generation file system could be used in Linux with FUSE, Mac OS X with Read/Write Developer Preview, FreeBSD and Solaris [wikipedia2008].
It is clear that NTFS supports most of the older OS like Windows NT and most of its family members etc. and NTFS were developed primarily as a modification of FAT 32. [pcmag2007]
In NTFS metafiles, define files, back up critical file system data, buffer file system changes, manage free space allocation, satisfy BIOS expectations, and track bad allocation units, and store security and disk space usage information.
It also Stores file owner, POSIX file permission, Creation timestamps, last access/read timestamps, Last metadata change timestamps, Access control lists, security/MAC labels, extended attributes/alternative data streams/forks and where as ZFS Stores file owner, POSIX file permissions, Creation timestamps, Last access/ read timestamps, Last metadata change timestamps, Last archive timestamps, Access control lists, Extended attributes/ Alternate data streams/ forks, Checksum/ ECC [wikipedia2008].
comparing the 2 paragraphs written above it states that the last archive timestamp is not stored in NTFS and where in ZFS the last archive timestamp is been recorded.
ZFS is considered as 100% dynamic in metadata because it has No limits on files, directory entries, etc. and No wacky knobs [opensolaris2006].
Comparison and Contrast of ZFS and NTFS
ZFS has its Maximum filename length as 255 bytes, allowable characters in directory entries are any Unicode except for NULL, Maximum pathname length has no limit defined, Maximum file size is 16 KB and the Maximum volume size is 16 KB [wikipedia2008].
The two has some similarities as shown above but ZFS has a unique feature that its maximum file name length has no limit and thus again ensures as a more precedence when compared with NTFS.
Naming Rules of the two file management system
Directory or Folder
What Solaris calls directory, windows XP calls it as a folder. This is an important comparison between the 2 file systems as it uses different terms.
Both file systems contain folders or directories (depending on what they call it) which in turn contain directories or folders. This is called hierarchical file system and is found in both file systems.
Directories / Folder Separator
Solaris uses the “ / “ Back slash as a delimiter and Windows XP uses “ \ “ forward slash as the delimiter. This is another distinguishable feature when comparing the 2 file systems.
In Solaris the root of the file system is depicted as “ / “. E.g. /home/eland/u2/klo33/file1
And in windows XP the root is always the physical drive. Windows support a notation of drive letters. E.g. C:\ , D:\, E:\
e.g. C:\Documents and Settings\asus\My Documents\1 SHAMIL IIT
I personally find it difficult to remember the drives which I have stored a file as windows physical drives uses adjacent characters like C, D, E etc. I usually get lost in finding a file in these drives. When using the UNIX file System, what I found interesting was that it always start with the root and had a particular sequence in addressing as /home/…. .
Extracting from the article posted by Barbara, (which appears in the document provided) it states that;
In windows XP the file names could be 254 characters long, while the file names in the UNIX could be 1023 characters long. [Babara2005].
But an article posted by IBM states that a path name identifies a file thus consists of directory names and a file name. A fully qualified file name, which consists of the name of each directory in the path to a file plus the file name itself, can be up to 1023 bytes long.
A UNIX file name could not alone hold a file name which is 1023 long thus it could hold 1023 characters with the full path name identifier of the file which consist of file name, directory name and etc. [publibIBM2006]
please click on any link on the Google ADSense bar and learn more on related topics
File organization and directory structure
UNIX has no concept of separate identifier for file partitions. So the Solaris UNIX use a network shared resource as its root directory.
Windows has a concept of separate identifier for file partitions. C, D, E etc.
I node in UNIX Solaris system stores basic information about a file, directory or other file system object. The file system maintains one I node table to keep track of any files placed on disk, and it can be seen as a sort of “index”.[wikipedia2006].
Methods of Files and Directory access.
total 3
-rw------- 1 leej 314 2 Jul 20 14:17 fredy
drwx--x--x 7 leej 314 512 Mar 2 12:45 publickill
drwx------ 10 leej 314 512 Jul 21 15:09 wordy
the column from left to write represents permissions (user,group,others) , number of links to file, owner, file owners group, size bytes, access date, time of last modified and file name.
[windowssitlibrary2005]
Granting and removing file permissions in UNIX is easy as users should only give in read, write and execute permission to user, group, others. Granting or removing permission is relatively easy as the user should type in a simple chmod command, where as in windows there are 5 types of permissions and it provides the same function where as UNIX provides.
Types of files in the Solaris UNIX and Windows XP
The meaning of file extensions
Windows file System consist of a base name, optionally followed by a dot and a filename extension of one to three characters e.g. test.cpp . the unix file system has no special rule as windows but could have more than one file extension such as .tar.gz Tarred-then-gzipped files [kb2007]. Or Docs.tar.zip
This style of multiple file name extension can’t be done in Windows. These multiple file name extension gives more detail to the document. For example .tar.gz file extension tells us that the document is Tarred-then-gzipped .
File and Disk Fragmentation
Algorithms are such that defragmentation is not an issue. ZFS keeps fragmentation to its minimum by writing related data blocks within the same cylinder group thus reduce seek time when the files are accessed. [sun2005]
In Windows NTFS when saving, files and folders get saved in pieces in different part of physical storage results in slowing the computers file input and output performance. I find this annoying as it makes much time in saving and retrieving files and ZFS has overcome this issue by keeping fragmentation to its minimum thus reducing seek time.
please click on any link on the Google ADSense bar and learn more on related topics
Finally as a summary ……….
The limitations of ZFS are designed to be so large that they will never be encountered in any practical operation. ZFS can store 16 Exabytes in each storage pool, file system, file, or file attribute. ZFS can store billions of names: files or directories in a directory, file systems in a file system, or snapshots of a file system. ZFS can store trillions of items: files in a file system, file systems, volumes, or snapshots in a pool. [opensolaris2006]
ZFS Pooled storage Up to 248 datasets per pool – file systems, iSCSI targets, swap, etc and File systems become administrative control points
ZFS has been subjected to over a million forced, violent crashes without losing data integrity or leaking a single block. [opensolaris2006]
These can’t be expected in NTFS thus ZFS was designed for robust, security and etc. and users find it difficult to use it and I suggest if Sun Microsystems could make it more user friendly as Windows it would make it more popular among people, but by considering all the facts mentioned above I’ll always stay with ZFS, because I consider it as the next generation file system !
You could also learn more on this topic by clicking any of the links provided in the Google AdSense column .
References
http://opensolaris.org/os/community/zfs/faq/ [accessed 14 April]
Opensolaris- ZFS Solaris file system
http://www.sun.com/emrkt/campaign_docs/expertexchange/knowledge/solaris_zfs.pdf [accessed 14 April]
NTFS file system
http://kb.iu.edu/data/affo.html [accessed 12 April]
NTFS nest generation file system
http://www.windowsitlibrary.com/Content/592/1.html [accessed 14 April]
[ZFS ]
ZFS
http://publib.boulder.ibm.com/infocenter/zoslnctr/v1r7/index.jsp?topic=/com.ibm.zconcepts.doc/zconcepts_177.html [accessed 14 April]
ZFS its uses
http://zamwi.com/2007/01/16/why-do-geeks-have-lust-for-zfs/ [accessed 13 April]
NTFS file system
http://www.pcmag.com/encyclopedia_term/0,2542,t=NTFS&i=48143,00.asp [accessed 14 April]
Opensolaris- last file system
http://opensolaris.org/os/community/zfs/docs/zfs_last.pdf [accessed 14 April]
Opensolaris- /solaris rises report.pdf
http://www.sun.com/software/solaris/solaris_rises_report.pdf [accessed 14 April]
[you say zeta I say]Bonwick, j
http://blogs.sun.com/bonwick/entry/you_say_zeta_i_say [accessed 14 April]
[wikipedia2008]
File_Allocation_Table
http://en.wikipedia.org/wiki/File_Allocation_Table [accessed 16 April]
[wikipedia2008]
ZFS
http://en.wikipedia.org/wiki/ZFS [accessed 14 April]
[wikipedia2008]
NTFS
http://en.wikipedia.org/wiki/NTFS [accessed 14 April]
[wikipedia2008]
Comparison_of_file_systems
http://en.wikipedia.org/wiki/Comparison_of_file_systems [accessed 15 April]
Subscribe to:
Posts (Atom)
