What Do Those 404 and Other HTTP Return Codes Mean?

You try to access a web page but all you get is a mysterious code number. What do they mean? This page attempts to address that topic.

Governing Document

Web standards are governed by documents prepared by standards committees, approved, and then implemented world-wide. Following are notes extracted from RFC2068Web Link, the draft governing document for the hypertext protocol.

Message Number Categories

Because you usually only see one or two error numbers it’s easy to believe that’s all there are. Actually, there are families of numbers; and, not all are errors. We’ll explore each family and its members below.

1xx Codes (Information). There are a few official codes in the one hundred range. But, if you see one you have probably stumbled onto some sort of experimental application. In this case, what you see will be non-standard and could be most anything.

  • 100 (Continue). An interim response telling the browser the initial part of its request has been received and not rejected by the server. A final response code should be sent when the remainder of the material has been sent.
  • 101 (Switching Protocols). The browser may wish to change protocols it’s using. If such a request is sent and approved by the server this response is given.

2xx Codes (Success). The two hundred range is reserved for successful responses. You probably won’t see one of these codes, but your browser will receive them and know that whatever request was sent by the browser was received, understood, and accepted.

  • 200 (OK). The request was successful and information was returned. This is, by far, the most common code returned on the web.
  • 201 (Created). If a POST command is issued by a browser (usually in processing a form) then the 201 code is returned if the resource requested to be created was actually created. If there is a delay in creating the resource the response should be 202, but may be 201 and contain a description of when it will be created.
  • 202 (Accepted). If a request for processing was sent and accepted but not acted upon and the delay in acting is unknown, then this code should be sent instead of 201. Note that 202 does not commit to processing the request; it only says the request was accepted. A pointer to some status monitor for the task is often included with this response so users can check back later.
  • 203 (Non-Authoritative Information). Usually the preliminary information sent from a server to a browser comes directly from the server. If it does not, then this code might also be sent to indicate that information did not come from a known source.
  • 204 (No New Content). The request was accepted and filled but no new information is being sent back. The browser receiving this response should not change its screen display (although new, and changed, private header information may be sent).
  • 205 (Reset Content). When you fill in a form and send the data, the server may send this code telling the browser that the data was received and the action carried out so the browser should now clear the form (or reset the display in some manner).
  • 206 (Partial Content). This code indicates the server has only filled part of a specific type of request.

3xx (Redirection). The 3xx codes indicate some need for further action by your browser. User action may or may not be necessary to cause this further action to take place; often it will just happen automatically. There are safeguards built into the specification designed to prevent infinite loops, which can sometimes result from automatic redirection.

  • 300 (Multiple Choice). You should not see 300 standing alone; it serves as a template for the following specific codes.
  • 301 (Moved Permanently). As the name implies, the addressed resource has moved and all future requests for that resource should be made to a new URL. Sometimes there is an automatic transfer to the new location.
  • 302 (Moved Temporarily). The addresses resource has moved, but future requests should continue to come to the original URL. Sometimes there is an automatic transfer to the new location.
  • 303 (See Other). The response to your browser’s request can be found elsewhere. Automatic redirection may take place to the new location.
  • 304 (Not Modified). In order to save bandwidth your browser may make a conditional request for resources. The conditional request contains an “If-Modified-Since” field and if the resource has not changed since that date the server will simply return the 304 code and the browser will use its cached copy of the resource.
  • 305 (Use Proxy). This is notice that a specific proxy server must be used to access the resource. The URL of the proxy should be provided.

4xx (Client Error). The 4xx codes are the ones you are most likely to actually see; particularly code 404. These codes indicate some sort of error has happened.

  • 400 (Bad Request). The server did not understand the request. This is usually cured by resending the request.
  • 401 (Unauthorized). The request requires some form of authentication (e.g., userid and/or password) but did not contain it. Usually, this code results in a box popping up in your browser asking you for the required information. Once you supply it the request is sent again.
  • 402 (Payment Required). Reserved for future use. [Who says the web is not moving toward being a commercial medium!]
  • 403 (Forbidden). This is a sort of catch-all refusal. If the server understood the request but, for whatever reason, refuses to fill it, a code 403 will often be returned. The server may or may not explain why it is sending a 403 response and there is not much you can do about it.
  • 404 (Not Found). If you happen to mistype a URL or enter an old one that no longer exists this is the error you will likely see. The condition may be temporary or permanent but this information is rarely provided. Sometimes code 403 is sent in place of 404.
  • 405 (Method Not Allowed). Your browser has requested a resource using a procedure not allowed to obtain that resource. The response should contain allowed procedures.
  • 406 (Not Acceptable). Your browser said only certain response types will be accepted and the server says the content requested does not fit those response types. (This is one way content monitoring can be implemented.)
  • 407 (Proxy Authentication Required). This code is similar to 401, except that the browser must first authenticate itself.
  • 408 (Request Timeout). Your browser waited too long and the server timed out. A new request must be sent.
  • 409 (Conflict). If a site allows users to change resources and two users attempt to change the same resource there is a conflict. In this, and other such situations, the server may return the 409 code and should also return information necessary to help the user (or browser) resolve the conflict.
  • 410 (Gone). Code 410 is more specific than 404 when a resource can’t be found. If the server knows, for a fact, that the resource is no longer available and no forwarding address is known, then 410 should be returned. If the server does not have specific information about the resource, then 404 is returned.
  • 411 (Length Required). For some processes a server needs to know exactly how long the content is. If the browser does not supply the proper length code 411 may result.
  • 412 (Precondition Failed). A browser can put conditions on a request. If the server evaluates those conditions and comes up with a false answer, the 412 code may be returned.
  • 413 (Request Entity Too Large). If your browser makes a request that is longer than the server can process code 413 may be returned. Additionally, the server may even close the connection to prevent the request from being resubmitted (this does not mean a phone connection will hang up; just that the browser’s link to the site may be terminated and have to be started over again).
  • 414 (Request-URI Too Long). You will likely not see this one as it is rare. But, if the resource address you’ve sent to the browser is too long this code will result. One of the reasons this code exists is to give the server a response when the server is under attack by someone trying to exploit fixed-length buffers by causing them to overflow.
  • 415 (Unsupported Media Type). If your browser makes a request using the wrong format, this code may result.
  • 451 (Unavailable For Legal Reasons). This status code indicates that the server is denying access to the resource as a consequence of a legal demand.

5xx (Server Error). The 5xx series of codes indicate cases where the server knows it has made an error or is not capable of answering the request. In most cases the server should include some information explaining the error and say if the situation is temporary or permanent.

  • 500 (Internal Server Error). An unexpected condition prevented the server from filling the request.
  • 501 (Not Implemented). The server is not designed (or does not have the software) to fill the request.
  • 502 (Bad Gateway). When a server acts as a go-between it may receive an invalid request. This code is returned when that happens.
  • 503 (Service Unavailable). This code is returned when the server cannot respond due to temporary overloading or maintenance. Some users, for example, have limited accounts which can only handle so many requests per day or bytes send per period of time. When the limits are exceeded a 503 code may be returned.
  • 504 (Gateway Timeout). A gateway or proxy server timed out without responding.
  • 505 (HTTP Version Not Supported). The browser has requested a specific transfer protocol version that is not supported by the server. The server should return what protocols are supported.

What Can Webmasters Do?

Users get frustrated by error messages that don’t really tell them anything. Even the descriptions above for the various return codes don’t say what you, the user, can do.

Webmasters can help. By analyzing their logs a webmaster can determine which error codes are being returned to users. For the most common, more descriptive error messages can be generated and the system told to use them. This latter is done using a file named “.htaccess” placed in the main directory for the web site. [.htaccess is used for Web hosts using UNIX or some UNIX offshoot.]

The .htaccess file can control many things, but to help with error messages the webmaster has only to insert line(s) of the form (each of these should be on a line by itself starting with “ErrorDocument” but they may be wrapped in this display):

  • ErrorDocument 402 “<h1>You have to BUY a <a href=”/subscribe.html”>subscription!</a></h1>
  • ErrorDocument 403 /forbidden.html
  • ErrorDocument 404 http://cknow.com/notfound.html

Note that the ErrorDocument command can have raw HTML code (note the leading quote only; no ending quote), file references, or URL references. Use whichever is appropriate to help users when they encounter errors at your site. If nothing else, include a 404 ErrorDocument command to help those who mistype something. If you don’t they may not come back!

If you want to really help (and keep the search engines happy), when you change your Web site layout consider adding “redirect” lines into the .htaccess file. These cause requests to specific files that have been moved to be automatically directed to their new location and gives feedback to the search engines that the URL has changed. There are two forms you can use:

  • redirect <oldfile> <newURL>
  • redirect permanent <oldfile> <newURL>

The first is for temporary changes (302 above) and the second for permanent changes (301 above). The <oldfile> should be replaced with the exact designation of the old file in relation to the root directory of the domain the .htaccess file applies to. The <newURL> should be just that: the full URL to the new page. This gives the search engines the ability to easily change their listings.

Comments from Original Article:

5/14/09
kamal
Said this on 2010-04-22 At 11:16 am
What Do Those 404 and Other HTTP? for the erros what the soulation
#2
DaBoss
Said this on 2010-04-22 At 11:36 am
In reply to #1
Contact the Webmaster for the website in question. The error messages come from the website so the Webmaster has to fix the site to get rid of them. Nothing you can do at your computer.

Things That Might Indicate Your Computer Is Infected

Despite the title, it’s important to note that if your computer is infected you may not have any indication of that infection. Much malware leaves no visible evidence of its presence. But, some does and below are a few of the things that should cause you to investigate further…

  • Your browser takes you to odd places. If a bookmark that has been directing you to your favorite site suddenly starts to direct you to another site that maybe tries to sell you something then the bookmark might have been hijacked by malware. Similarly, if you type in a URL but get taken to a completely different site address that should raise your suspicions.
  • You try to access your anti-virus software but can’t. A number of malware beasts will attempt to turn off your anti-malware protections (e.g., anti-virus software, adware detectors, etc.). Often they are successful and sometimes will even deactivate any shortcuts to the program(s). If you’ve tried to access your anti-malware software and can’t, that’s another reason your suspicions should be raised.
  • You start seeing ads but your browser is not active. If ads start to pop-up on your system without any reason you should be very suspicious. Even worse, if these pop-ups say your computer is infected and attempt to sell you a solution, don’t wait. Immediately find out what sort of malware you have and get rid of it. That’s pretty much a dead giveaway malware is afoot.
  • Your social media sites start showing posts from you that you didn’t write. Fake postings on social sites are a strong indication your computer is infected. Their purpose is to get your friends and followers to click on links in the post so that your friends and followers might become the next victim. Do them a favor and investigate your system for malware.
  • Systems tools are unavailable. One of the ways to investigate what’s running on your system is to use the Task Manager and other related system tools to see what programs and processes are running. It’s not a foolproof method because many legitimate processes have really odd names. But, if you can’t open these tools at all via an administrator account then you should seriously look into the possibility your computer is infected.
  • Friends start to call you about being stranded on your trip to [insert any far-away place]. One of the payloads in malware is to send E-mails to your address list and other mail addresses found on your system. A popular messages appears to be from you saying that you are stranded in some exotic place and you are asking them to send money to help you get back home. The instructions are to wire it to some location. The problem is you are not there and once you wire money from your bank account you can’t usually get it back. Calls like these from correspondents should be a clear sign you have an infection.

There are probably other subtle signals you could look for (e.g., system runs very slow, the internet connection or hard disk seems particularly busy for no apparent reason, etc.) but the ones above or indications similar to those are pretty common signs of an infection. Get some anti-virus software and check your system as soon as any of these show up. Better, have some running before the infection to help keep your system clean.

Hardware Threats

Hardware is a common cause of data problems. Power can fail, electronics age, add-in boards can be installed wrong, you can mistype, there are accidents of all kinds, a repair technician can actually cause problems, and magnets you don’t know are there can damage disks.

Hardware problems are all too common. We all know that when a PC or disk gets old, it might start acting erratically and damage some data before it totally dies. Unfortunately, hardware errors frequently damage data on even young PCs and disks. Here are some examples.

Power Faults

Your PC is busy writing data to the disk and the lights go out! “Arghhhh!” Is everything OK? Maybe so, maybe not; it’s vital to know for sure if anything was damaged.

Other power problems of a similar nature would include brownouts, voltage spikes, and frequency shifts. All can cause data problems, particularly if they occur when data is being written to disk (data in memory generally does not get corrupted by power problems; it just gets erased if the problems are serious enough).

  • Brownout: Lower voltages at electrical outlets. Usually they are caused by an extraordinary drain on the power system. Frequently you will see a brownout during a heat wave when more people than normal have air conditioners on full. Sometimes these power shortages will be “rolling” across the area giving everyone a temporary brownout. Maybe you’ll get yours just as that important file is being written to disk.
  • Voltage Spikes: Temporary voltage increases are fairly common. Large motors or circuit breakers in industry can put them on the electrical line. Sudden losses (e.g., a driver hits a power pole) can causes spikes as the circuits balance. An appliance in your home can cause a spike, particularly with older wiring. Lightning can put large spikes on power lines. And, the list goes on. In addition to current backups and integrity information for your software and data files, including a hardware voltage spike protection device between the wall and your computer hardware (don’t forget the printer and monitor) can be very helpful.
  • Frequency Shifts: While infrequent, if the line frequency varies from the normal 60 Hertz (or 50 Hertz in some countries), the power supply on the computer can be affected and this, in turn, can reflect back into the computer causing data loss.

Solution: Consider a combined surge protector and uninterruptible power supply.

Age

It’s not magic; as computers age they tend to fail more often. Electronic components are stressed over time as they heat up and cool down. Mechanical components simply wear out. Some of these failures will be dramatic; something will just stop working. Some, however, can be slow and not obvious. Regrettably, it’s not a question of “if”, but “when” in regard to equipment failure.

Solution: Keep an eye on the specials after three to five years.

Incompatibilities

You can have hardware problems on a perfectly healthy PC if you have devices installed that do not properly share interrupts. Sometimes problems are immediately obvious, other times they are subtle and depend upon certain events to happen at just the wrong time, then suddenly strange things happen! (Software can do this too!)

Solution: Make a really good backup before installing anything (hardware or software) so you can revert the system back to a stable state should something crop up.

Finger Faults

(Typos and “OOPS! I didn’t mean to do that!”)

These are an all too frequent cause of data corruption. This commonly happens when you are intending to delete or replace one file but actually get another. By using wild cards, you may experience a really “wild” time. “Hmmm I thought I deleted all the *.BAK files; but they’re still here; something was deleted; what was it? Or was I in the other directory?” Of course if you’re a programmer or if you use sophisticated tools like a sector editor, then your fingers can really get you into trouble!

Another finger fault problem arises with touchpads below the space bar on notebook computers. It’s very easy to brush the touchpad when you are typing away and suddenly find yourself entering characters in a screen location very different from where you were before you touched the pad.

Solution: Be careful and look up now and again to make certain your cursor is where you want it.

Malicious or Careless Damage

Someone may accidentally or deliberately delete or change a file on your PC when you’re not around. If you don’t keep your PC locked in a safe, then this is a risk. Who knows what was changed or deleted? Wouldn’t it be nice to know if anything changed over the weekend? Most of this type of damage is done unintentionally by someone you probably know. This person didn’t mean to cause trouble; they simply didn’t know what they were doing when they used your PC.

Solution: Never run the computer as an administrative user and have guest accounts available for others who use the computer. Keep up-to-date backups as well.

Typhoid Mary

One possible source for computer infections is the Customer Engineer (CE), or repairman. When a CE comes for a service call, they will almost always run a diagnostic program from diskette. It’s very easy for these diskettes to become infected and spread the infection to your computer. Sales representatives showing demonstrations via floppy disks are also possibly spreading viruses. Always check your system after other people have placed their floppy disk into it. (Better yet, if you can, check their disk with up-to-date anti-virus software before anything is run.)

Solution: Insist on testing their disk before use or make certain they’ve used an up-to-date anti-virus before coming to your location.

Magnetic Zaps

Computer data is generally stored as a series of magnetic changes on disks. While hard disks are generally safe from most magnetic threats because they are encased within the computer compartment, floppy disks are highly vulnerable to magnets. The obvious threat would be to post a floppy disk to the refrigerator with a magnet; but there are many other, more subtle, threats.

Some of the more subtle sources of magnetism include:

  • Computer Monitor. Don’t put floppy disks anywhere near the monitor; it generates a magnetic field. (Generally applies to the older CRT displays.)
  • Telephone. When ringing, telephones (particularly older phones with a bell) generate a magnetic field.
  • Bottom Desk Drawer. While the desk drawer does not generate a magnetic field, the vacuum cleaner that the maintenance people slide under the desk to clean the floor does.
  • Bottom Bookcase Shelf and File Cabinet Drawer. Same comment as the desk drawer just above.
  • Pets. Pet fur generates a strong electrostatic charge which, if discharged through a disk, can affect files on the disk. Instead of “The dog ate my homework,” today it could just as easily be: “The cat sat on my homework.” (I once had a student where this exact problem happened; a cat sat on her floppy disk and static wiped out the data on the disk.)

Solution: Stay away from magnets or sources of static of all kinds when working with a computer.

Bottom line: There are tools to assist in recovery from disk problems, but how do you know all the data is OK? These tools do not always recover good copies of the original files. Active action on your part before disaster strikes is your best defense. It’s best to have a good, current backup and, for better protection, a complete up-to-date integrity-check map of everything on your disk.

Summary

  • There are many different kinds of hardware threats to your data. Some include:
    • Power faults
    • Age
    • Equipment incompatibilities
    • Typos
    • Accidental or deliberate damage
    • The Customer Engineer or friendly salesperson
    • Problems with magnets and/or sources of static electricity
  • Active action on your part can help you identify problems and, perhaps, head them off early.
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How to Use File Shredder to Permanently Delete Files

In the article “How to Securely Delete a File” we saw that using Windows to delete a file is not the way to do so securely. To completely delete a file you have to overwrite it multiple times with different patterns; something Windows has no capability to do. In this article we discuss how to use the free program File Shredder to securely delete files. [Click on pictures to expand them.]

File Shredder is a program that allows you to securely shred one or multiple files using algorithms up to the Guttmann 35-overwrite algorithm. The program will also overwrite and clear all of the free space on a disk and, if you wish, will install a link to the program into the right click context menu for Windows Explorer so that if you are in Explorer and right click on a file you will have an option to shred it or mark it for later shredding.

Installing File Shredder is easy. It comes with a Windows installer that operates much like any other Windows installer. The program installs into the C:\Program Files\File Shredder\ directory by default but you can change that if you need to.

Once installed, to start the program you need only double click on the program icon and you see the main screen…

File Shredder 01 Program Screen

The left menu controls the actions of the program. You have links for adding files or folders or removing them from the file list in the right side of the screen. Below those is a link to shred free disk space and below that is a link for Shredder Settings. That’s the first one you want to take so you can make the program behave as you wish…

File Shredder 02 Settings Dialog

If you want to have the File Shredder option appear in the right click context menu for Windows Explorer make certain the first box is checked. Because file shredding completely removes a file from your system you should also make certain the confirmations are all checked. If you were to make a mistake without confirmation the program would execute your command and if it’s a file you really wanted to keep they you’d have to restore from backups (you do keep backups don’t you!?). With confirmations at least you will have a second chance to bail out before making a mistake.

The Algorithms tab in the Settings dialog allows you to select the exact method you want used to overwrite and “shred” files…

File Shredder 03 DoD Setting

The DoD 5220-22.M standard of three passes over the file with specific patterns is the default selection. Unless you have very sensitive files to delete this will likely do. To recover anything at this level would require very advanced techniques and may not even be possible then. It’s also the fastest secure algorithm in the options. The other two to consider would be the 7 and 35-pass algorithms. These certainly will be more secure than the DoD but will take that much longer to execute. Your choice however. Use what you feel comfortable with.

The Visual Options tab presents options on how the program looks when started…

File Shredder 04 Visual Options

These should be pretty obvious selections. You likely want the program to be visible when you choose to run it and does anybody really want a small utility program to fill the entire screen when it starts???

After shredding individual files you might want to clear the free space on your hard disk. Why? Because the hard disk is divided into sectors of a given length and if a file does not have enough data to fill the last sector written to then whatever was in that sector stays on the disk and could be accessible to any utility that reads the disk byte by byte. If it just happens to be part of a previous version of your password file that data could be useful to someone. The link to clear free space is just above the Settings link in the left menu. When clicked you see the drives on your system…

File Shredder 05 Shred Free Disk Space

Check the one(s) you want to clear the free space on and then select the algorithm to be used. As before, the DoD is probably good enough for most uses unless you are really paranoid or have things that just should not see the light of day on your system. When done setting things up, click on the Next button…

File Shredder 06 Start Menu

The next screen provides some summary information with a Start button. Once the Start button is clicked the free space shredding begins. This can take significant time to complete depending on the size of your disk, the number of files on it, and a variety of other factors specific to each computer system. Do not start this process if you can’t let the computer run. The program will give you an option to abort the process if you need to but even that takes a bit of time while the program cleans up after itself before stopping the process.

Now that things are set up, let’s see the program in action. CKnow set up a test machine and ran the program against several copies of the same 2.4 megabyte file using different algorithms and captured the results in a Flash video. The results can be viewed by clicking on the graphic below…

Well, not quite yet. Still have to edit the video.
[Coming Soon]

Finally, File Shredder will add a shortcut to the right click context menu for Windows Explorer if you told it to do so in the settings above. This gives you the option of having quick access to the program from Explorer…

File Shredder 07 Secure Delete Files

You can see the result in the graphic above where CKnow right clicked on the File Shredder icon and then selected that option. You have the option to immediately shred the file in question using the defaults presently set in the program, mark the file for later shredding, or opening the program itself with the file selected.

That’s File Shredder in a nutshell. Interested in the program? Go to their page and read more or downloadWeb Link.

This article is part of a series about secure file deletion. The others in the series include: “How to Securely Delete a File” and “How to Use Moo0 FileShredder to Permanently Delete Files“. Related would be the article “What Files to Delete to Maintain Your Privacy [Coming Soon].”

Original TUTOR(dot)COM

In 1985, Computer Knowledge prepared a basic tutorial about microcomputers and DOS. The exercise was to help students and to help me learn programming. The first goal was somewhat successful; the second, not so much as I look back on the code. 🙂

One of my ultimate goals is to recreate that tutorial in different form and updated to today’s technology. But, in the process, I thought it might be of interest to see the original. I picked the 1991 version as one of the last versions in the original format.

The original was a DOS-based program that displayed text-only pages, one page at a time. You could navigate the pages and at times the program would ask questions and expect an answer.

TUTOR.COM Color Selection When started, the program would go through a setup routine and asked if you wanted to view the text in color or monochrome and if you wanted sound or not. The sound was just simple beeps; nothing fancy.
TUTOR.COM Main Menu You were then presented with the tutorial’s main menu. There were nine different choices plus zero to exit the program. The choices are duplicated below and each will take you to a page where you can browse a gallery of screen shots for that topic. Enjoy…

TUTOR.COM Main Menu

  1. Tutorial which explains TUTOR.COM (version 4.5).
  2. A description of the expanded keyboard.
  3. Brief history of computers.
  4. Introduction to computers, binary numbers, and the CPU.
  5. Introduction to storage and input/output devices.
  6. Disk Operating System operation and commands.
  7. A tutorial on subdirectory structure and commands.
  8. Batch file commands and structure explained.
  9. A brief introduction to structured programming.

Additionally, you could start the program with the parameter OLDKEY and this would cause the #2 keyboard tutorial to switch from the expanded keyboard to the original IBM-style keyboard. That one is here…

Tutorial Which Explains TUTOR.COM

A tutorial that explains the TUTOR.COM program itself and includes the shareware order forms (with address information redacted since it’s now free). This tutorial is left as part of the complete archive but, frankly, you can probably skip it and not even notice you’d done so. 🙂

Below are the 15 screenshots that make up this tutorial. Click on each thumbnail to expand it and/or move through all 15 (assuming you have JavaScript active for this site).

Introduction 001 Title Screen Title screen: Notes on TUTOR.COM.
Introduction 002 How to Use TUTOR.COM How to use the TUTOR.COM program.
Introduction 003 Answering Questions The answer capability.
Introduction 004 User Menu The user menu.
Introduction 005 What is TUTOR.COM What is the TUTOR program?
Introduction 006 Why Register Why register?
Introduction 007 What You Receive More about what you receive.
Introduction 008 How to Register How to register?
Introduction 009 Basic Order Form Basic order form.
Introduction 010 License Only Option License only order form.
Introduction 011 Site License Site license order form.
Introduction 012 Credit Card Authorization Credit card payment form.
Introduction 013 Out-of-US Registration Out of U.S. registrations.
Introduction 014 Support Support.
Introduction 015 End Screen That’s all there is to it!

The Expanded Keyboard

A tutorial that explains the expanded keyboard (the keyboard with the function keys at the top).

Below are the 22 screenshots that make up this tutorial. Click on each thumbnail to expand it and/or move through all 22 (assuming you have JavaScript active for this site).

Enhanced Keyboard 001 Title Page Title screen: Notes on The New Enhanced PC Keyboard.
Enhanced Keyboard 002 Keyboard Differences Summary of the two keyboard types.
Enhanced Keyboard 003 Sections Function keys.
Enhanced Keyboard 004 Introduction Function keys (continued).
Enhanced Keyboard 005 Buffers Buffers.
Enhanced Keyboard 006 F1 and F3 F1 and F3.
Enhanced Keyboard 007 F2 and F4 F2 and F4.
Enhanced Keyboard 008 F5 F5.
Enhanced Keyboard 009 Caution Important program note.
Enhanced Keyboard 010 Function Key Summary Keyboard test of lessons learned.
Enhanced Keyboard 011 Function Key Test Another little test.
Enhanced Keyboard 012 Number Entry Cursor control and number entry.
Enhanced Keyboard 013 Curson Control Cursor controls.
Enhanced Keyboard 014 Cursor Control Cursor controls (continues).
Enhanced Keyboard 015 PageUP PageDown Example PageUp/PageDown
Enhanced Keyboard 016 Control and Alt Control and Alt keys.
Enhanced Keyboard 017 Pause and Stop and Restart Keystroke combinations (keychords).
Enhanced Keyboard 018 Shift and CapsLock Shift and CapsLock.
Enhanced Keyboard 019 Escape and Enter Escape and return keys.
Enhanced Keyboard 020 Tab and Backspace Tab and backspace.
Enhanced Keyboard 021 Print Screen PrintScreen.
Enhanced Keyboard 022 Endnotes End notes

The Original Keyboard

A tutorial that explains the original IBM keyboard (the keyboard with only 10 function keys on the left side).

Below are the 23 screenshots that make up this tutorial. Click on each thumbnail to expand it and/or move through all 23 (assuming you have JavaScript active for this site).

Old Keyboard 001 Title Page Title screen: Notes on The PC Keyboard.
Old Keyboard 002 Function Keys Function keys.
Old Keyboard 003 Alphanumeric Keys Alphanumeric keys.
Old Keyboard 004 Numeric Keypad Numeric keypad.
Old Keyboard 005 Discussion Keyboard overview.
Old Keyboard 006 Buffers Buffers.
Old Keyboard 007 F1 and F3 F1 and F3.
Old Keyboard 008 F2 and F4 F2 and F4.
Old Keyboard 009 F5 F5.
Old Keyboard 010 Caution An important note.
Old Keyboard 011 Function Key Summary A short test.
Old Keyboard 013 A Function Key Test Another little test.
Old Keyboard 014 Numeric Keypad Cursor controls.
Old Keyboard 015 Insert Delete PgUp PgDn Cursor controls (continued).
Old Keyboard 016 PageUp PageDown Example PageUp/PageDown.
Old Keyboard 017 Control Alt Control and Alt.
Old Keyboard 018 Control Key Combinations Keystroke combinations (keychords).
Old Keyboard 019 Shift and CapsLock Shift and capslock.
Old Keyboard 020 ESC Return/td>

Escape and carriage return.
Old Keyboard 021 Tab and Backspace Tab and backspace.
Old Keyboard 022 PrintScreen PrintScreen.
Old Keyboard 023 Enhanced Keyboard Preview Enhanced keyboard.
Old Keyboard 024 Endnotes End notes

History of Computers

A tutorial that summarizes the history of computers.

Below are the 18 screenshots that make up this tutorial. Click on each thumbnail to expand it and/or move through all 18 (assuming you have JavaScript active for this site).

History 001 Title Page Title screen: Notes on Computer History.
History 002 Introduction Introduction and references.
History 003 Beginning The beginning.
History 004 Babbage Babbage and The Countess of Lovelace.
History 005 Babbage Contribution Babbage’s contribution.
History 006 Hollerith Herman Hollerith and the 1890 census.
History 007 World War II World War II.
History 008 First Generation The generations: first.
History 009 Second Generation The generations: second.
History 010 Third Generation The generations: third.
History 011 Fourth Generation The generations: fourth.
History 012 Microcomputers Microcomputers.
History 013 Early 1970s Microcomputers (continued).
History 014 1974-75 Microcomputers (continued further).
History 015 1976-77 Micros: the 70’s continue.
History 016 End of 1970s Closing out the 70s.
History 017 1980s The 1980’s.
History 018 Future The future.

Computer Terms (Part 1)

A tutorial that summarizes the basic terms associated with computing. Binary numbers are introduced as well as a basic description of what makes up a computer.

Below are the 21 screenshots that make up this tutorial. Click on each thumbnail to expand it and/or move through all 21 (assuming you have JavaScript active for this site).

Computer Terms 001 Title Page Title screen: Definitions of Computer Terms, part 1.
Computer Terms 002 Introductory Notes Introductory notes.
Computer Terms 003 What Computers Do What computers do.
Computer Terms 004 Best Computer Uses What is the computer best at?
Computer Terms 005 Hardware vs Software Hardware versus software.
Computer Terms 006 Computer Systems Computer hardware.
Computer Terms 007 Division of Hardware Division of hardware.
Computer Terms 008 Basic Hardware Elements Basic hardware elements.
Computer Terms 009 Computer Hardware Elements Hardware element diagram.
Computer Terms 010 Quiz Time out for a quiz.
Computer Terms 011 Time Coming to terms with time.
Computer Terms 012 Nibble or Byte When you eat do you Nibble or Byte?
Computer Terms 013 Basic Binary Binary numbers introduced.
Computer Terms 014 Binary Numbers Binary to decimal conversion.
Computer Terms 015 Many Bytes Start counting from zero.
Computer Terms 016 Addressing Addressing.
Computer Terms 017 CPU in Detail The CPU in detail.
Computer Terms 018 Registers Registers.
Computer Terms 019 CPU Operation CPU diagram.
Computer Terms 020 Today's CPUs Today’s CPUs.
Computer Terms 021 Summary Let’s rest now!