Basics of how email works

I have noticed that some of my friends are not really aware of just how email works. This isn't really necessary -- as long as it works the way one "expects". It only becomes a problem when it does NOT work the way that it is expected.

Email starts out the same way as paper mail. It has an address and it has a letter (or body). It may even include some type of contents (attachment). The actual format of an email body is only important for a corporate systems administrator -- you'll probably never have to worry about it. The way attachments are carried may be of interest but, once again, it will work for you or it won't work for you. One popular method is MIME (Multipurpose Internet Mail Extensions) which allows mixing various types of files (photos, movies, music, text, etc.) within the same email file.

An address consists of a user id an "at" sign and a mail server name. A server is a computer which provides services to other computers (possibly in addition to providing services to someone directly using the computer). These services can be acting as remote data servers or it can be as a mail server. A mail server acts as a post office with each individual user id acting to identify an individual post office box. Popular mail servers include gmail.com, att.net, verizon.net, charter.net, yahoo.com, and aol.com. These people-readable, "friendly", names are actually translated into machine-friendly numbers (such as 103.56.113.114) by a system of other servers which provide domain name services (DNS). These machine addresses are used by the Internet Protocol (IP) network to route messages to the correct servers.

Most mail servers act as a "post office" for many different user ids. However, it is always possible for you to have a computer in your own home that acts directly as a mail server for your own domain name. When you send mail to someone, it is routed to the mail server for that address. The computer that acts as the mail server may be located anywhere -- Ohio, Paris, London, Florida, Washington state, or wherever. The mail will stay on that server until someone "picks it up" and then deletes it (or the mailbox capacity is exceeded). The important point is that, for most people, the email actually exists on some other computer that may be far away.

In order to pick up your email, you have two basic options. You can use a browser (or other program) to connect directly to your mail server and read/delete/send mail. Or you can use a mail program (such as Outlook, Thunderbird, Mac Mail, or AOL) to connect to the mail server and download the mail on the server to the computer upon which you are typing. At the point of downloading, there are still two copies of the email -- one on the mail server and one on your local computer. However, this is a waste of storage space, so most mail programs give you various options (under "options" or "preferences" usually) to delete the copy of the email on the mail server. This can be done immediately, in three days, in a week, or an arbitrary interval.

And now you have your email and can deliberate on a thoughtful response.

http://technoglot.blogspot.com

What makes high tech "high"?

People, and the media, talk a lot about "high tech"? But what is high tech? Warren Buffett says that he does not invest in high tech -- not because he thinks that it is bad but because he feels that it is wisest to invest in companies that one understands. This allows a good understanding of the business and the market and the managerial capability to run the company.

High tech exists because of all of the levels of technology upon which it relies. Thus, it is at the apex (or top) of a very large pyramid. This is reflected by our education and what we are expected to be able to do at different periods of our education.

At the bottom of the pyramid are "simple machines" and, as listed in Susan Kristoff's "Introduction to Simple Machines", scientists in the Renaissance period listed six devices for simple machines. These are the lever, the wheel and axle, the pulley, the inclined plane, the wedge, and the screw. In order to create, or make use of, simple machines, a variety of "simple tools" are required -- such as hammers, screwdrivers, wrenches, pliers, saws, and shovels. To this list, I would add cutting instruments such as knives and chisels.

Of course, when you read through lists such as this, you will find yourself saying -- but what about scissors, and bolts, and nuts, and ...? Just because the Renaissance scientists made a specific list of six items doesn't mean that everyone will feel that is THE correct list. For example, I could argue that the wedge and the inclined plane are variations on the same thing. I would actually be tempted to classify into categories of mechanical movement such as lifting, pushing, pulling, and rotating.

It really doesn't matter. The fact is that there are some basic machines and tools that exist at the bottom of the pyramid. By using such basic devices, we can produce "low tech" -- a swing set, a door, a teeter-totter (for those that remember such ), pogo sticks, and so forth. These can all be easily built using basic devices and tools. Of course, the degree of "finish" for something will depend on the quality of the tools and the experience of the craftsperson. I can create hinges and a door but you probably wouldn't want it on the front of your house.

We now reach into the "middle technology" category. Note that things are not REALLY so nicely divided as something may easily be broken into parts that are of various levels of needs. When we get to middle technology, we get to phonographs (for those who remember such), steam engines, paddlewheels, flour mills, ships, and so forth. These are items where you might appreciate the work which goes into them but aren't likely to cause you to gasp with astonishment. And many moderately experienced modern young adults can probably make such. They take knowledge, tools, and the ability to design and follow directions. I could probably make a horrible sounding, but functional, record player (and record). Neither Bose nor Boston Acoustics will lose sleep over that.

Now, we come to high tech. High tech requires the use of middle tech tools and machines to create their products. A CD player requires the ability to create lasers, and smoothly precise rotating movements, and a lot of semiconductor chips, and wiring and special metals and materials. I could NOT create a CD player without first creating a lot of things that I would need prior to being able to create the CD player. High tech requires middle tech which requires low tech. And that is the real story -- high tech builds upon other techs.

http://technoglot.blogspot.com

Computer Literacy 101 -- what is a peripheral?

A computer system cannot often stand alone -- it needs a way to input data, it needs a way to output data and it needs a way to expand its capabilities. These devices are called peripherals. A keyboard is a peripheral. A monitor is a peripheral. The time panel on a microwave oven can properly be called a peripheral, although it may be part of the overall design and not optional.

Peripherals can be grouped in classes. One class is Input/Output (or I/O). These peripherals allow you to put in (input) data or to access (output) data. Another class would include removable storage systems -- a flash card, a hard disk, a CD-ROM unit. Other classes exist.

Input devices have a particular requirement from the operating system. Since it is unknown just WHEN data will be input, there must be a way for the operating system to notice that data are available. The two main ways of doing this are via polling and via interrupts. A poll is a periodic check for data -- like a child in a car asking "Are we there yet?". An interrupt is like a tap on the shoulder. Different systems will use different methods. A poll does not take long but there will be many times that the answer will be "no" -- and, thus, the time taken is "wasted". An interrupt takes much more time because it is necessary to save the current situation (maybe you're in the middle of a program) before the interrupt can be handled. Let's say that handling an interrupt takes 50 milliseconds and a poll takes 1 millisecond. If an event occurs once a minute, then doing an interrupt will take less time than polling once a second (50 < (60 x 1)). However, if the event occurs twice a minute, then polling is more efficient (50 > (30 x 1)).

A keyboard is an input peripheral. So is a mouse. In the case of a keyboard, a specific data value is sent when a key, or combination of keys, is pressed. This is usually kept in a temporary memory buffer that can be read by another program that is currently accepting input from keyboards (maybe a word processing program, maybe a browser window). A mouse sends two types of information -- a change in location and key presses. The key presses are handled similar to those of a keyboard. However, the change in location is done by the computer keeping track of the "location" of the mouse. When the computer starts up, the mouse is considered to be in a "default" (starting) location (often the upper left of your monitor). If you move your mouse to the right, it keeps track of how far to the right it has moved. Note that it isn't usually a one-to-one movement or your mouse pad would have to be as large as your monitor. Also, if you pick up the mouse and move it, it is as if it never moved.

Printers and monitors are typical output peripherals. Printers are fairly straightforward (although the actual data may not be such) -- your output may say "give me a new page", "print the letter 'a'", "go to the next line", and so forth but it basically is given a set of commands in sequence. A monitor, currently, is more complicated because of the idea of active windows and locations. So, in a modern operating system, the computer not only needs to keep track of where the mouse (as reflected by the cursor displayed on the monitor) but what program is making use of input while the cursor is at that location and what menu or button must be activated if there is further input (keyboard or mouse click) while at a specific location within that program's active space (or window). The input devices are actually what are causing changes about what you see -- the monitor just reflects the effects of that input.

And that pretty well covers Computer Literacy 101 -- though I would be happy to try to address any areas (of the many) that I have neglected.

Computer Literacy 101 -- what is an operating system?

An operating system (or OS) is a special program that allows other programs to run. This is the core of a general purpose computer -- the ability to run programs that are not pre-determined. A specialized computer (or microprocessor) may be able to run multiple programs but they are known in advance and, thus, the system can be designed to just run those programs (simpler, faster, and smaller).

As a more general definition, an operating system manages the resources of a computer. Sometimes, it is defined by a hierarchical model (sometimes known as the "onion" model) because there are services that are provided by the primary section of the operating system. Then there is another layer that provides new services plus makes use of the primary section. Then another layer that makes use of the other two layers, and so forth.

Some of the services provided by an operating system (in "layer order") are task (program) management, memory management, process (tasks communicating with one another) management, device management (such as hard disks, or CD-ROM drives, and so forth), and finally file management.

Because the applications make use of operating system services, which in turn rely on other "lower layer" services, most applications are not portable between different operating systems. This is why a program that works with Windows (a particular operating system) may not work on a Macintosh (running Mac OS X, a different specific operating system) or under a system running UNIX or Linux (two closely related operating systems).

There is an apparent exception to this -- but it really still follows the same rules. If one uses a browser that executes a program within the browser, that program may work with browsers running on computers using different OSs. It appears to be OS independent (able to work under any operating system) but, actually, it is making use of a set of services that have been defined to have the same use on multiple operating systems. Because this set of services, or interface, between the program and the next layer is the same, the program can run under different operating systems -- but the underlying program that provides that interface is still operating system dependent.

There is little agreement on what Operating System is "best". In general, the one that provides the services that you need, and the applications you need, for the lowest price and greatest speed is "best" for you. (It may not be the best for someone else with different needs.)

Computer Literacy 101 -- what are programs?

Data falls into two categories, as we saw in the previous blog. These categories are instruction data and program data. Instruction data can also be called a program -- which makes use of the program data to fulfill its purpose. Many times, a program will be called an application. Most people refer to programs as applications if they are widely used by different people. A word processing program may be considered an application. A spreadsheet program may be considered an application. Programs that people do not directly make use of are usually not called applications.

Programs consist of a sequence of instructions that tell the computer what to do. In the first blog of this series, we mentioned the types of instructions that may be given a microprocessor. These instructions are called machine language because they are sets of datum that are interpreted directly by the microprocessor. For example, the decimal value of 026002 will tell an HP 2100 computer to "jump" (change the current address for the next address) to address 002. The 026 portion is a "change the current instruction address to" code for the microprocessor and the 002 portion tells it the new value for the instruction address. Frankly, you don't really want to know much more than that unless you are involved with microprocessor design. Most microprocessors have their instructions written in binary (0s and 1s) or hexadecimal (symbols 1 through F for each numerical location) but the computers of the "early days" were not always standardized.

There is a hierarchy of languages used to program computers. At the base is machine language -- normally represented by a series of 0s and 1s -- like 10011001100011100011111101011110 -- which would be considered 32-bits. Current-day programmers almost never use machine language directly. The next level is called assembly language which uses a set of readable codes that can be directly translated into machine language. An example of assembly language might be "JMP START", where JMP is the operation to be performed and START is a symbol for an address that is the value to be used by the operation. The next level consists of many different languages in a family called high-level computer languages. A compiler changes the high-level language into assembly language (or, sometimes, directly into machine language. An assembler changes the assembly language into machine language. Finally (at least, at this current point of time) there are machine-independent languages which are used to create programs that may be run on many different computers without being changed.

Programmers write programs. Very few write machine language programs. More, but not many, write assembly language programs. Most write programs in high-level languages. An increasing number write programs in machine-independent languages (such as Java). However, all of them end up actually creating machine language -- with special programs such as Java interpreters/compilers, compilers, and assemblers acting to make it into this special, final, form.

I said earlier that some programs are visibly used by people -- and these are called applications. The ones that are NOT visibly used by people are sometimes called system programs. These are programs that enable to computer to perform the acts that people want. A printer program will be used to allow people to print a document from their application. At the core of all of the system programs is a particular program called an operating system and this will be addressed in the next blog.

Computer Literacy 101 -- what are data?

All computers work with data. But, what are data? I say "what are data" because the word data is a plural one -- it is the plural of datum. However, almost no one ever uses the word datum and just about everyone treats data, grammatically, as singular. A datum is a single piece of information -- yes or no, it is raining or it is not raining, you have eaten breakfast or you have not eaten breakfast. You will note that a datum only indicates a yes/no or off/on, binary, condition. Most of the time, when we need information, it is really a collection of datum -- or data.

The same is true with computers -- they work on each individual datum but they pull them out of a pool of data. This data (I will use the conventional singular grammar here) is kept in storage, as I pointed out in a previous blog. It is then transferred from one storage area to the local RAM where the microprocessor can directly work with it.

Data is used by the microprocessor at many stages. The first stage, or startup (or bootup), is when the microprocessor first receives electricity. The actual hardware (the collection of semiconductor chips, and other discrete electronic components) is designed to start transferring data from a specific memory storage area and address. Often, this is address zero (0). This means that the microprocessor will transfer data from address 0 (the actual physical location, once again, depends on design of the hardware) to its working memory. It then executes the data -- it starts to perform specific operations based on the contents of that data that was at that address and then increments the address for the next instruction (usually by one -- unless the first instruction says something else) and then executes the operations for that address and on and on.

The next stage occurs once the registers (we talked about them in the storage blog) of the microprocessor have been filled with working data. At this stage, it is prepared to continue to execute instructions as it transfers them from memory. You can look at is as having two stages -- the first where the microprocessor "wakes up" with no specific contents in its registers and the second when the microprocessor has been initialized and can now proceed to work as the data tells it. Or, you can look at it as having three stages -- the first one the boot stage, the second is the startup stage where it is still getting ALL of the hardware connected to the computer ready to be used, and the third stage where any type of instructions can be executed because all of the hardware has been set up to be ready for use.

All of this works with the data. The data, for a general purpose microprocessor, is what makes it able to work differently each time it is turned on. For a specialized microprocessor, the incoming data starts the activities for which the microprocessor is designed.

Somehow, I managed to avoid the word program in this description but data are often split into two categories. Instruction data, or programs, are executable -- they contain instructions for the microprocessor while program data is used by the programs to produce more data. The difference between these categories of data is that instruction data does not change (unless someone specifically writes another program to change that instruction data -- the topic of viruses and software patches).

I'm going to swap the next two items on my original "computer literacy" list and talk about programs more in the next blog.

Computer literacy 101 -- what is memory?

We talked about the microprocessor, or CPU, of a computer last blog -- but what can it do without someplace to store, and retrieve, information (next entry will talk about how that information -- or data -- is used)?

The first thing to know about memory for computers is the idea of address space. Address space serves the same purpose for computers as postal addresses do for paper mail. Often that address space will start at zero (0) and continue to as large as the physical memory allows. As an example, you have a 4GB flash drive that you use for assignments -- carried between home and work, or classes. The addresses of the information on that flash drive will be from 0 up to 4 gigabyte - 1 (or
actually 4,294,967,295 but you can think of it as 4,000,000,000 units of information).

You also may have many different locations for memory -- these are called storage units. So, you may have a hard drive, a DVD-ROM drive, a USB flash card, and a set of backup files on a tape unit. Using the comparison to the paper mail system, let's say that each of these are in a different city -- so addresses consist of the information location (0 to 4 gigabyte on the flash drive) and storage location "G:flash_drive".

Alright, this is pretty cumbersome and it can really strain a microprocessor to directly address 4 gigabyte of memory (although it is possible for computers that describe themselves as "64-bit processors"). So, what most computer systems do is to break this memory down into separate "blocks" (or streets in the mail system). Each block may consist of 512 bytes. Therefore, we can now address a block as "G:flash_drive", "block 0 to 8,388,607" and a specific location as "G:flash_drive", "block 1,567", "byte 93".

OK. We see that by numbering the information and then breaking it down into separate groups we can effectively find all the information. But it is still rather clumsy talking about "G:flash_drive", "block 1,567", "byte 93". That is where the file system comes into play. A file system starts putting all of those numbers into friendlier terms. "Charles resume" is a lot easier to remember when one is doing a word processing program than telling it -- give me "C:CKS_hard_drive", "block 7,432 through 7,987", "bytes 0 (of first block) through 345 (of last block)".

Not only that, but this specific labeling of the location makes it very hard to move it -- what if I add something to the information (or file)? It will get bigger and the location will also get bigger -- do I now have to remember a whole new set of numbers? No. The file system will keep track of just where the file is now located and how large it is. (It also means that the file does not have to be contiguous -- the bytes can be located in different blocks and not come one after another.)

There are two other regions of memory that should be understood -- these are RAM and registers. Random Access Memory (RAM) is like your own pile of papers on your desk. It can be gotten to very quickly and is "right there". Registers are like "post-its" and are used for temporary copies of numbers to be used. RAM will often be addressed just by the byte numbers and registers will be referred to by special names (R1 for register 1) -- but these details aren't really important to most people.

Now that we have information in memory, how do we use it? That is the concept of data.

Computer literacy 101 -- what is a computer?

Back from jury duty (actually, jury selection -- I didn't have to serve). I am going to start my short series on areas that I feel are important to become computer literate. I will try to make it useful but not to go into greater detail than necessary.

A computer, of today, is based on a semiconductor chip called a microprocessor. This is also sometimes referred to as a CPU (Central Processing Unit). This microprocessor changes numbers. It does very simple things with the numbers -- moves them from one location to another, shifts them (which effectively multiplies them by 2 or divides them by 2), does "logic" operations on them (which, if you don't know what that is -- will be another topic in the future), and changes the order in which it follows directions depending on the values that it has been given or has created based on the instructions given. That's about it, although some microprocessors will have other instructions that are actually shortcuts for a sequence of operations that could be done with a long series of simpler instructions.

The microprocessor does simple things with the numbers -- but it does them very, very quickly. When you see an advertisement for a "4 GHz CPU", it is an indication of how fast the microprocessor is and an indication of how quickly instructions can be processed. Larger numbers indicate a greater potential for speed. I say potential because the final speed depends on many design factors but, in general, you can use these numbers as an indicator of speed.

Microprocessors are used in many devices in our modern world. When they are in something that allows its use for different, non predetermined, purposes, it is called a "general purpose computer" or just plain old computer. Most people are familiar with smaller computers that are referred to as Personal Computers (PCs) but computers come in many sizes from a "smart" cell phone to a large "mainframe" which might be as large as several filing cabinets (they keep getting smaller, though).

The other category of use of microprocessors is for specialized uses -- the microprocessor is used for only one thing, or for one category of uses. Televisions, amplifiers, DVD players, watches, digital clocks, refrigerators, coffee makers, fuel injection and engine monitoring systems, traffic lights, alarm systems and MP3 players are all examples of devices using specialized processors. Some devices start entering into a "grey" area where they could be used for various, non-predetermined, purposes but are actually primarily used for a single purpose.

The microprocessor does not exist just by itself. It must have access to ways of giving it information upon which to work and ways to give results. In order to do this, other electronic devices will be connected to it and they, in turn, will be connected to other devices. A digital watch is an example of a very "simple" system which has buttons for setting information and a display to give results.

One very important additional item to which the microprocessor must have access is memory, which will be the topic of the next blog.

Computer Literacy?

My 10-year-old, fifth grade, son came to me the other day -- he had a micro SD disk that he said had cheat codes on it that he wanted to use for some Wii games. I connected up my card reader to the USB connection on the Windows machine and looked at the files. I looked -- and then I rewatched the Youtube tutorial on how the program was supposed to work -- then I said to him "OK, this is the data file -- where is the program?" He responded "what is a program?".

Admittedly, only people with a historical bent are truly interested in how I started programming with little toggle switches on the front of a DEC computer -- or the huge decks of punched cards that I used in college to meet the needs of my programming classes. But, I do think that children who are in a school with a computer lab and multiple computers in the classroom should not be asking "what is a program?" by the time they're in fifth grade. And it's a good school.

Computer literacy seems to be interpreted as the ability to use particular programs (even if they don't know what a program is). My son did a couple of PowerPoint presentations last year for class and he's used Microsoft Word for a few papers. He has no problem in using a browser (even if he doesn't know what a browser is) and searching for information with Google. BUT, I still maintain that it is hard to transfer skills from one program to another without knowing some computer basics.

Many of the readers of this blog will already know most of this -- but I'm going to use my next week of blogs to talk about computer basics that I, personally, think ought to be known to be computer literate.

Subjects will include:

What is a Computer?

What is memory, files, and storage?

What are data (besides being a character on Star Trek: The Next Generation)?

What is an operating system (all my children keep complaining when a Windows program won't work on the family Macintosh)?

What are programs and how do they work?

What are peripherals -- what is I/O?

And any other topic that comes up within this realm. I once wrote a book ( never published) on computers and how they work -- let's see if I can summarize in a set of reasonably sized blogs.

Smart plugs, dumb plugs, and dumb designs

I read a lot of emails, and articles in the magazines I read, about the next way to save electricity.

Some of these are related to the problem of passive power loss. This occurs when an electrical appliance is plugged in but is not actively in use. If designed well, then they will not use any power when they are turned off -- but what is off?

Any device that can be turned on by a remote is not completely without power. Any device that maintains an active clock (not powered by batteries) is not completely without power. And, in today's world, that makes up a large percentage of the electrical devices in our houses.

A "smart" electrical strip is designed to have one unit on a power monitoring circuit. The remaining outlets are triggered to provide power only if the monitored outlet starts consuming electricity beyond a certain level. For example, a television might be plugged into the monitored outlet. When it is "off", it only requires a certain level of power but, when on, it greatly increases the electricity needed. At this point, the other outlets become active. A DVD player, for example, might be plugged into a "client" outlet and the television into the monitored outlet. Until the television is turned on, no power is given to the DVD player (and the remote will not work with it).

Unfortunately, this is very limited in its uses. A DVR cannot be plugged into a client outlet because it runs timed events (an active clock). Same is true with a VCR. It MIGHT be useful with an amplifier or receiver but not with a satellite receiver which requires passive checks for updates of data over the phone lines. Every potential scenario must be carefully examined.

I purchased a "Kill-A-Watt" power monitor via a "Gold sale" on amazon.com. It seems to be designed well (with a few not-too-important caveats) but I have been unsuccessful in tracking down the largest electrical uses within the house. I thought that my study -- with four computers, a printer, LAN, and quite a few other individual devices (such as hard drives and powered disk readers) was surely the culprit. But it wasn't -- so the "Kill-A-Watt" was useful to disprove that. I now believe that the main drains are the pool pump and the house fans -- usually direct wired and often badly inefficient and expensive to replace.

So, how to reduce electricity use? Unplug those items not in use (some DO use power even when "off"). Run as many items though an Uninterruptible Power Supply (UPS) as possible in a study -- a UPS will act as a buffer for items on reduced power demand. Reduce the number of internal clock devices. Keep the lights off when not in use. Use fans that have energy star ratings if possible -- and keep energy use in mind when purchasing new items.

It's not easy to drive green

As the joke goes, the simplest way to drive a green car is to take it into the body shop for a new paint job. Personal automotive transport just isn't the overall best way to reduce carbon output. Walk, bicycle, ride public transportation, skateboards, pogo sticks -- fill it in.

But folks love having their own "wheels" -- the freedom to go when and where they want and not have to take a long time in the process. So, recognizing that it'll never be the "best" solution, what are the ways to make it as green as possible?

First thing to do is to recognize that there are two different statistics involved with the eco-friendliness of transportation. These are the local carbon footprint and the overall effects on the environment.

On the local carbon footprint, matters are fairly clear. If you use a traditional gas/diesel engine, get one that has the best MPG. Next down comes hybrid cars -- which have an "extra" in that they pollute less when stopped at an intersection. Yet cleaner (locally), are natural gas, all electric, hydrogen, and solar (not quite feasible yet -- but perhaps soon).

So, if everyone drives an electric car, there will be no more pollution and the world will be saved. Right?

No, not that simple. Of course, there is the fact that private transportation is only part (albeit an important part) of the climate problem. But the big problem is that it doesn't cover the overall effects on the environment -- which are NOT easy to determine and which are not always immediately "obvious".

The June 2008 issue of Wired mentions that manufacture of batteries for hybrid cars has a BIG carbon footprint. I don't have the issue nearby but it offsets the carbon savings from using a hybrid by many years (5 to 10, as I recall). So, a Smart car is still a better bet -- in spite of the excitement of hybrid.

What about the zero-emission alternatives? Well, they have to manufactured. They also need roads to drive on. They need parking spaces (take a peek from Google Earth and just see how much of the land is occupied by roads and parking spaces -- especially in cities). And, except for yet-to-be-viable solar cars, their fuel still needs to created and transported.

Let's say that you have an all-electric car. How is that electricity produced? Is is a solar farm or a geothermal plant? Well, probably not (though possible). The electricity is produced and the conversion of energy is not 100% efficient (it varies a lot depending on design and fuel). Wikipedia indicates that there is a little over 7% loss in transporting over the electrical grid.

Depending on many factors -- such as how eco-conscientious the power producer may be, that electric car may actually have a larger carbon footprint than a Smart car. (I keep using a Smart car as an example -- if you prefer, just exchange that for a "very small, efficient internal combustion car".)

I used electric cars as an example but the same analysis holds for hydrogen cars.

The bottom line is that it's not easy to drive green -- so check the first paragraph for truly better alternatives. Then, if that doesn't fit with your life, organize your trips to reduce miles. Get as small of a car as works for you -- rent something for those "once a year" situations. Live and work locally if at all possible. Reduce the miles driven and spend more time with your friends and family.

Most of all, keep the "big picture" in mind. Don't feel guilty -- act responsibly.

From cordless to mobile

Apologies for taking so long to resume my posts. Frankly, it was a bit difficult to feel like posting when it seemed like no one was paying any attention. But, I've decided that that is no reason not to post, and I really appreciate the feedback from my one (perhaps only ) reader -- thank you Leda. Please, everyone, do tell me about what you are interested.

Last post, I talked about going into the details of what makes a mobile/cellular phone different from a cordless phone. There really isn't that much real difference. The primary differences are distance between the handset and the base station and the fact that each base (cell) station will handle more than one phone. In addition, there is a need for handover (handoff) of the phone from one base (cell) station to another as one moves around.

When one uses a cordless phone, it must synchronize with the base station. To do this, it may require cycling between "channels" to find a clear connection. However, it is still a relatively simple connection -- usually no need for identification or security.

A cell phone goes through a number of stages. When it is powered up, it basically "shouts" into the air and these transmissions are omnidirectional (unlike a satellite link, the handset may be in any position relative to the base station) so the signal must go all directions. Although it is possible for carriers to share a pool of transmission frequencies, it is more common for a single carrier to use a set of frequencies. So, the phone shouts out within this bandwidth and waits for a response.

The cell station listens and then, using identification information found in the initial transmission from the mobile handset, sends back a response. It is possible that a further exchange of information (called a handshake) will take place to further identify the specific phone and the services available to that handset. This process is known as registering. Much of the registration information will reside in the memory (or specialized memory -- known as a SIM) of the handset. The first time you use your handset, much more information is exchanged to build up the store of data in the handset.

Once registered, people can call you and you can call others. Signal strength (or number of "bars") will make a difference about the clarity of the call. However, calls are really made between the base station and the other phone -- not the handset. The handset is the final destination/origination of the data (voice or email or whatever) but the call is really between the base station and the other end (peer).

The base station may make an additional jump to a more powerful station or it may directly connect into the wired "landline" phone networks. At some point, almost all mobile calls are actually routed via landlines. It is just more efficient to use the Radio Frequency (RF).

The ability to do the "handover" is what really disctinguishes a mobile phone from a cordless phone. As you move, with your handset, the signal strength from the current base (cell) station will change. If it decreases, it may reach the point where the signal just isn't strong enough to continue the call. When the signal strength decreases, the handset will start shouting again. If it finds a new, stronger, base station, it will initiate the "handover", which is basically the same thing as a "transfer" from a non-mobile phone. The call is transferred from the old base station to the new base station and it will then act as the primary endpoint for the call (with data continuing to be exchanged with the handset).

This transition must be done very quickly to allow an interrupted use of the circuit. Because of this transition delay, the handset and base station may behave a bit differently if a data session is in use -- perhaps setting a lower signal strength trigger for handover and waiting for a pause in data to do the transfer.

Of course, all this doesn't actually work as simply as described. In particular, the RF transmission and reception are very difficult areas to engineer. Although I have taken enough physics and engineering courses to understand, in principle, how the RF works, my general impression is that RF engineers are magicians.

So, that is really the difference between a cordless phone and a mobile phone -- the ability to do that transfer (handover) as smoothly as possible.

I leave you at that point but will try to post on a much more regular basis.