This guide is a brief introduction to collecting data communications terminals that communicate over a serial interface, generally referred to as serial terminals.  Serial terminals can be organized as generations of technology: electromechanical, video display, vector graphics, dot matrix printing, and multipersonality.  X Window System or "X terminals" and thin client Windows computers are extensions of the general principal of terminals and are briefly mentioned at the end of this guide.

The Idea Behind Terminals

The idea of the terminal has always been to create an inexpensive interaction point with a computer for people to use.  Starting in the 1960s, instead of submitting a card job to an I/O desk and waiting for your job's printer output you could interact directly with the computer through a terminal.  The terminal could be located in a more comfortable environment than the climate controlled machine room where the computer was kept. 

The terminal evolved to include more sophisticated local processing and then technology took an interesting twist.  The terminal experience evolved into the personal computer experience, with immediate response to the user's input.  Local processing had taken over the entire experience.

Meanwhile, mainframe and minicomputers were also gaining new processing power and there was still a need for a low-cost interaction point with these larger machines.  There was still a need for a terminal, but most often the job was now done with a terminal emulation program running on a personal computer.  The pressure of the personal computer has forced terminals to become lowest cost commodity devices in order to earn their keep even as they expand their capabilities. 

Electromechanical

The electromechanical generation of data terminals evolved from early telegraph and teletype machines.  Computers of the 1960s and 1970s were commonly used with the ASR-33 Teletype.  The teletype typically uses a 20mA current loop interface, while later generations would switch to an RS-232 voltage based interface.  The 20mA current loop interface would persist as an interface option for many terminals in order to maintain compatability with the teletype.

The teletype converts data signals into electromechanical signals that drive a mechanical typing assembly.  Interaction with a teletype is line-by-line, entering information on the typewriter like keyboard and signalling the end of input with the return key.  The text is printed on roll paper, and in a pinch you could substitute the coarse brown paper rolls from a bathroom towel dispenser and it would work.  The print mechanism is quite loud. When you hear that characteristic mechanical typewriter noise used as a sound effect for "news broadcasts", it is most likely the mechanism of an ASR-33 that you are hearing.

Teletypes were classified by their capabilities with the following acronyms:

• RO - receive only
• KSR - keyboard send and receive
• ASR - automatic send and receive

The RO teletype contained no keyboard and printed the received data stream, acting as a remote printer.  The KSR teletype contained a keyboard into which data could be typed as well as the printing mechanism for reception.  The ASR teletype added the paper tape reader/punch unit to the KSR.

Teletype Corporation's model ASR-33 teletype, circa 1963

Video Display

Digital Equipment Corporation's VT-05, 1970

While a teletype interacts with you line-by-line, a video display terminal presents a "screen" of information to you all at once.  A typical screen might measure 80 characters wide by 24 lines high.  Inside the terminal is a cathode ray tube (CRT), similar to a television tube.  Circuitry in the terminal reads the data for the screen from a memory bank and converts the characters into signals for the CRT.  The glyph for each visible character is stored as a bitmap pattern in a character ROM.  The refresh circuitry reads out the bitmap pattern from the ROM and uses it to modulate the electron beam inside the CRT.  The front of the CRT is covered by phosphorous compounds that are excited by the electron beam and emit light as they revert from an excited state to a normal state.  The light you see coming from the monitor is from excited phosphorous compounds!

When the phosphor compounds return to their normal state, they stop emitting light.  In order to present what you perceive as a stable image, the CRT has to be refreshed fast enough that your eyes can't tell that the image is strobing.  Most people don't notice any flashing in an image that is refreshing at 60 Hz.  The higher the refresh rate, the easier it is on the eyes and 75 Hz is a common refresh rate that many people find more comfortable on the eyes than 60 Hz.

The very first video display terminals used discrete logic for the video refresh circuitry and had very limited capabilities.  The simplest of these provided enough intelligence for clearing the screen and scrolling the lines upwards.  The introduction of the microprocessor allowed for the first "intelligent" video display terminals.  One very popular early intelligent video display terminal was the VT-100, manufactured by Digital Equipment Corporation or DEC.  The VT-100 became so popular that other manufacturers created terminals that were compatible with the control codes for a VT-100.  It is testimony to the market strength of the VT-100 that this compatability is retained in virtually all terminals manufactured since.

Video display terminals first appeared in the 1960s with early TTL logic models soon followed by microprocessor controlled models.  From the 1960s through the 1980s, terminals took on a wide variety of case shapes.  As the control electronics became smaller and smaller, the need for a larger case was no longer required to the point where the electronics making up the video refresh circuitry now fit in a case not much larger than the CRT tube itself.

Digital Equipment Corporation's VT-100, 1978

Vector Graphics

The video display CRT was just one of many different kinds of tube and phosphor combinations used for the presentation of information.  Early tube displays appeared in oscilloscopes and were driven directly by voltages that controlled the deflection of the electron beam horizontally and vertically.  A variation on the CRT is called the storage scope display.  With a storage scope display, a smaller bias voltage is applied continuously to the tube.  When the electron beam is moved across the phosphors, the extra charge hits the tube and is "stored" as a pattern of charge in the phosphor coating.  As long as the bias voltage is maintained, the charge pattern will remain and cause the phosphor to emit light.  In this way vector graphics can be drawn as charge patterns in the phosphor by controlling the horizontal and vertical movement of the electron beam.  In a storage scope display, the refresh circuitry need only keep the bias voltage applied, there is no need to scan the image over and over again onto the phosphors.  A storage scope display does not flicker like a CRT, instead the phosphors emit light continuously.

One early manufacturer of storage scope based display terminals was Tektronix.  Their terminals had a characteristic green phosphor and made very high resolution vector graphics possible.  The downside of a storage scope display is that there isn't any way you can remove the extra charge from a portion of the display; it is necessary to erase the entire display all at once by applying a large "reset" voltage to the phosphor coating.  It was possible to draw a few vector shapes dynamically by applying less than the full power to the electron beam necessary to store a charge pattern on the tube.  In this way you could have a dynamically updating portion of the display on top of the static background.

Tektronix storage scope displays were used to provide the computer graphic effects in the original "Battlestar Galactica" series in the late 1970s.  At that time, they were state of the art in computer graphics displays.  Tektronix was one of the most successful vector display vendors.  Their model 4010 vector graphics terminal was so popular that many manufacturers emulate the control codes for this terminal to display vector graphic plots.

Tektronix Inc.'s 4010

Dot Matrix Printing

Around the same time that the dot matrix video display terminals were first created, the dot matrix printing terminals appeared.  These terminals were similar to KSR teletypes and included a keyboard and printing mechanism.  The print mechanism was a column or grid of pins under computer control.  A pin pushed outwards through a hole to press a ribbon against the page and print a single dot.  Each glyph is formed by a bitmap pattern in a character ROM which is used to drive the pins to print the glyph.  This mechanism was considerably faster than a teletype.  The entire print mechanism was under microprocessor control and allowed for effects such as underlying, italics, superscripts and subscripts which would be impossible on a teletype.

Early dot matrix printing terminals embodied an entire "desk" and the user sat down at the terminal like sitting at a typewriter desk.  These terminals typically used tractor feed fanfold paper unlike the plain rolls of paper used in a teletype.  Later examples of dot matrix printing terminals were desktop models.  Digital Equipment Corporation (DEC) manufactured several generations of printing terminals of the pedestal and desktop variety, such as the LA-36 and LA-120 terminals.

Multipersonality

With faster microprocessors and more terminal manufacturers entering the marketplace, the terminals manufactured from the 1980s onward began to include emulations of other terminals.  The terminal had accumulated enough processing power to reinterpret the control codes of other terminals and perform the equivalent operation.  The current behavior of the terminal was determined by the personality it was emulating.  Most modern terminals have a number of personalities they can exhibit by emulating the control codes of another terminal.

Wyse Inc's WY-325

X Terminals and Thin Clients

In the 1980s, networked workstations with bitmapped graphics displays, mice and ethernet networking was becoming the norm for engineering facilities.  However, it was expensive to buy a workstation for every engineer.  The widespread adoption of the X Window System provided some new life into the terminal concept.  Terminals with bitmapped displays, mice and ethernet networking, but no local storage or programming, ran the X Window System and acted as an interaction point for a network computing and storage infrastructure.  This is the concept of the "X terminal".  Early examples such as the NCD 16 by Network Computing Devices, integrated the keyboard, mouse, networking, display processor and CRT.  The most recent examples consist only of a display processor and use standard PS/2 compatible keyboards and mice and a standard SVGA monitor.

The idea of a "thin client" is similar to that of an X terminal or personal computer.  A thin client usually runs a version of Windows or an OS based on Java.  In all cases, the intention is to present the user with a familiar graphical interface to their work, while the storage and program execution happens somewhere else on a server on the network.

Collecting Terminals

We all have our own reasons for collecting.  For most people, they collect the terminals that they might have used early in their exposure to computers.  A few people collect terminals to get equipment that is of the same period as other elements of their collection.  For instance, it would have been common to use early personal computers such as the Altair with an ASR-33 teletype.

Some people collect terminals that have an interesting shape or look.  The Lear Siegler ADM-3A has a characteristic "60s feel" to the case and doesn't look anything at all like a modern Wyse WY-50.  Some people collect terminals that have interesting capabilities, such as the Tektronix storage scope display vector graphics terminals.

Video display terminals are the ones offered most frequently on ebay.  As always, prices will be determined by the buyers and sellers.  Sometimes the price will be bid up quite high and other times an item will languish unbought.  As with most "collectible" items on ebay it pays to observe for a while and see what is typical before diving in over your head.

Shipping Video Terminals

Shipping a serial terminal involves two problems: weight and fragility.  The CRT tubes in video terminals give them enough weight that they have to be packed carefully for shipping.  The mass of the CRT tube can cause the item to shift during handling and can cause the mounting posts or case to become damaged.  Some of the larger units may require freight shipping due to their size and weight.  There are two important elements involved in shipping a terminal: the box and the cushioning.

The Box

Use a brand new sturdy double-wall cardboard box from a shipping supply store.  Do not reuse a box that was used to ship something else; a new box doesn't cost much and will preserve the condition of your vintage terminal.  It is important to use a double-walled cardboard for its strength.  A single-walled cardboard box will crumple from the weight during handling and can rip open too easily.

The box should be large enough to allow approximately 3 inches of cushioning space around all sides of the unit and room for the keyboard.  Don't forget to account for space around the top and bottom of the unit.

The Cushioning

A minimum of 3 inches of cushioning should be provided around all sides of the unit.  The unit must be cushioned against vibration and shock forces encountered during shipping.  Imagine a pissed off package service delivery worker picking your box up off a conveyor belt and throwing it into a delivery truck.  To guard against such handling, the unit needs to be cushioned against vibration and rough handling.

The best kind of cushioning is to fill the space around the terminal with expanding foam packing.  A plastic liner bag is inserted into the box and the expanding foam is sprayed from an aerosol can into the plastic liner.  The liner is folded over and while the foam is still soft, the unit is placed onto the closed plastic liner.  The soft foam conforms to the shape of the unit and the plastic liner keeps the foam from sticking to the box or the unit.  This is repeated with another liner on the top of the unit.  The foam hardens enough to cushion the unit and protect it from damage during shipping.  Upon receipt the buyer will open the box, remove the top foam packing layer and then remove the unit from the packing.

If you don't have access to expanding foam for shipping, then bubble wrap and packing peanuts can be used.  It is important to use the large sized bubble wrap (1" bubbles are good) to adequately cushion the terminal within the shipping box.  Do not use hard blocks of solid styrofoam.  It doesn't provide sufficient cushioning for the terminal and leaves large voids which will cause items to shift during delivery.  Pack the item in the box:

1. Apply bubble wrap around all sides of the unit and secure with tape.
2. Fill the cardboard box with packing peanuts to a uniform depth of approximately 3 inches.
3. Place the unit on the center of the bed of packing peanuts.  The best orientation is with the bottom side of the unit to be in its normal orientation.  If this is not possible, align the unit with the heavier portion near the bottom.
4. Fill the remainder of the box with packing peanuts around all sides.  Wiggle the box back and forth during filling to allow the packing peanuts to settle into all the areas around the terminal.  Lightly compress the peanuts with your hand around the sides of the unit.
5. Fill the remainder of the box with the packing peanuts to slightly overfull.  If you can easily close the lid of the box, sprinkle a handfull more of peanuts on top until there is slight resistance against closing the lid.  This ensures that the peanuts are securing the unit from all six sides of the box.
6. Close the lid of the box and tape securely along all seams of the lid.  Most boxes have a top seam where the two lid flaps meet in the center and two side seams where the top folds over to join the sides along the corners.

The package itself should always be marked fragile to avoid it being mishandled during shipping.  You can buy preprinted red fragile labels at most shipping supply stores.

To summarize, when shipping a video terminal:

1. Use a new double-wall cardboard box that allows 3 inches of cushioning around the terminal on all sides, top and bottom.
2. Always mark the package fragile.
3. Wrap the unit in bubble warp.
4. Use sufficient cushioning material in the box around all sides of the unit.
5. Secure the box well.

If you are not confident that you can pack the terminal for safe shipping, take the terminal for packing at a shipping handler like UPS, Federal Express, etc.  They have the necessary items in ready supply and have packed many items for safe handling before.

Shipping Teletypes and Printing Terminals

Teletypes and printing terminals with integrated steel pedestals involve their own special problems for shipping.  They tend to be very heavy, often in excess of 150 pounds.  Parcel carriers like UPS and Federal Express will not ship these items and you will need to contact a freight service for shipping.

See my other guides:

• Beehive Terminals
• DEC Terminals