ADM-3A
Encyclopedia
The ADM-3A was one of the first computer terminal
s manufactured by Lear Siegler
, first produced in 1975. It had a 12 inch screen displaying 12 or 24 lines of 80 characters.
enabling it to emulate a Tektronix 4014
and an extension port which would allow daisy chaining several ADM-3As on a single RS-232
line.
The ADM-3A's overall setup was controlled by 32 DIP switch
es under the nameplate at the front of the machine, beside the keyboard, including speed from 75 to 19,200 baud. The advanced configuration options allowed split speed connection, sending at one rate, and receiving at another.
Compared to the ADM-3, the ADM-3A was also much more controllable. It supported control codes to move the cursor around on the screen, and directly position the cursor at any point in the display. It did not, however, support “clear to end of line” or “clear to end of screen”, or other more advanced codes that appeared in later terminals, such as the VT52
and VT100
.
The 5×7 dot matrix characters were displayed in amber, green, or white phosphor
on black (the cursor was 7×9). The keyboard had 59 keys. The 12-inch monochrome
CRT
was mounted in the top half of the clamshell case, and was typically made by Ball Brothers
.
Unlike later terminals, such as the VT100
, the ADM-3A did not use a microprocessor in its implementation, but instead used TTL logic. It did, however, use RAM chips, rather than the Circulating Memory used by earlier terminals, such as the Datapoint 3300
.
character for the "Home" directory in the C shell
, bash and other command shells on Unix
and Unix-derived systems derives from the ADM-3A's having the tilde
symbol and the word "Home" on the same key, and it was the dominant terminal in the Computer Science and Engineering department at the University of California, Berkeley
when Bill Joy
originally wrote the C shell.
Similarly, the use of the HJKL keys for moving the cursor in the vi
editor and its descendants also stems from the ADM-3A; it had the cursor-movement arrows printed on those four keys.
Both the arrows and the "home" correspond to the functions of the corresponding control characters Ctrl-H, Ctrl-J, Ctrl-K, Ctrl-L, and Ctrl-^ (identical to Ctrl-~) when sent to the terminal, moving the cursor left, down, up, right, and to the "home" position in the upper left-hand corner of the terminal, respectively. (The Ctrl-H and Ctrl-J functions were standard, but the interpretations of Ctrl-K, Ctrl-L, and Ctrl-^ were unique to the ADM-3A.)
Finally, the control key
was located above, not below, the shift key
-- in the same place where most modern PC keyboards put the Caps Lock key. Many standard Unix key combinations were designed with the QWERTY layout and the ADM-3A's original Ctrl key placement in mind. Many of those key combinations are still in use today, even on non-Unix operating systems. Seasoned computer users familiar with the original layout often claim that the different position of the Ctrl key on modern PC keyboard layouts makes the use of Ctrl key combinations more cumbersome. Solutions exist for many operating systems to switch around the Caps Lock and Ctrl keys in software, thus making the PC keyboard layout more closely resemble the ADM-3A's keyboard layout.
Computer terminal
A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system...
s manufactured by Lear Siegler
Lear Siegler
Lear Siegler Incorporated was created as a result of a merger between the Siegler Corporation and Lear Avionics Inc. that was concluded in 1961. John G. Brooks was the founder; President and Chairman of Siegler and William Lear was the founder; President and Chairman at Lear...
, first produced in 1975. It had a 12 inch screen displaying 12 or 24 lines of 80 characters.
Details
Originally priced at $1195, a DIY kit later sold for $995. The original model, the ADM-3, only displayed capital letters; this was quickly supplanted by the more advanced version with both lower and upper case. Versions of the terminal were available where the display showed only twelve (rather than twenty-four) rows of eighty characters—in those days, RAM was expensive, and halving the display size halved the RAM requirement (and likewise all uppercase required only six bits per character to be stored rather than seven). Further optional add-ons included a graphics cardVideo card
A video card, Graphics Card, or Graphics adapter is an expansion card which generates output images to a display. Most video cards offer various functions such as accelerated rendering of 3D scenes and 2D graphics, MPEG-2/MPEG-4 decoding, TV output, or the ability to connect multiple monitors...
enabling it to emulate a Tektronix 4014
Tektronix 4014
The Tektronix 4000 series was a family of text and graphics computer terminals based on the company's storage tube technology. No additional electronics were needed to maintain the display, so the 4000 series were less expensive than earlier graphics terminals and became widely used in the CAD...
and an extension port which would allow daisy chaining several ADM-3As on a single RS-232
RS-232
In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
line.
The ADM-3A's overall setup was controlled by 32 DIP switch
DIP switch
DIP switches are manual electric switches that are packaged in a group in a standard dual in-line package...
es under the nameplate at the front of the machine, beside the keyboard, including speed from 75 to 19,200 baud. The advanced configuration options allowed split speed connection, sending at one rate, and receiving at another.
Compared to the ADM-3, the ADM-3A was also much more controllable. It supported control codes to move the cursor around on the screen, and directly position the cursor at any point in the display. It did not, however, support “clear to end of line” or “clear to end of screen”, or other more advanced codes that appeared in later terminals, such as the VT52
VT52
The VT52 was a CRT-based computer terminal produced by Digital Equipment Corporation introduced in September, 1975 . It provided a screen of 24 rows and 80 columns of text and supported all 95 ASCII characters as well as 32 graphics characters. It supported asynchronous communication at baud rates...
and VT100
VT100
The VT100 is a video terminal that was made by Digital Equipment Corporation . Its detailed attributes became the de facto standard for terminal emulators.-History:...
.
Hardware
Phosphor
A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
on black (the cursor was 7×9). The keyboard had 59 keys. The 12-inch monochrome
Monochrome monitor
A monochrome monitor is a type of CRT computer display which was very common in the early days of computing, from the 1960s through the 1980s, before color monitors became popular. They are still widely used in applications such as computerized cash register systems...
CRT
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
was mounted in the top half of the clamshell case, and was typically made by Ball Brothers
Ball Brothers
The Ball brothers were the founders of the Ball Brothers Glass Manufacturing Business which eventually became Ball Corporation. They greatly improved the quality of life of Muncie, Indiana through their philanthropy and business. They were instrumental in the creation of Ball State University, and...
.
Unlike later terminals, such as the VT100
VT100
The VT100 is a video terminal that was made by Digital Equipment Corporation . Its detailed attributes became the de facto standard for terminal emulators.-History:...
, the ADM-3A did not use a microprocessor in its implementation, but instead used TTL logic. It did, however, use RAM chips, rather than the Circulating Memory used by earlier terminals, such as the Datapoint 3300
Datapoint 3300
The DataPoint 3300 was the first computer terminal manufactured by the Computer Terminal Corporation , announced in 1967 and shipping in 1969...
.
Legacy
The short-hand notation of using the tildeTilde
The tilde is a grapheme with several uses. The name of the character comes from Portuguese and Spanish, from the Latin titulus meaning "title" or "superscription", though the term "tilde" has evolved and now has a different meaning in linguistics....
character for the "Home" directory in the C shell
C shell
The C shell is a Unix shell that was created by Bill Joy while a graduate student at University of California, Berkeley in the late 1970s. It has been distributed widely, beginning with the 2BSD release of the BSD Unix system that Joy began distributing in 1978...
, bash and other command shells on Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
and Unix-derived systems derives from the ADM-3A's having the tilde
Tilde
The tilde is a grapheme with several uses. The name of the character comes from Portuguese and Spanish, from the Latin titulus meaning "title" or "superscription", though the term "tilde" has evolved and now has a different meaning in linguistics....
symbol and the word "Home" on the same key, and it was the dominant terminal in the Computer Science and Engineering department at the University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
when Bill Joy
Bill Joy
William Nelson Joy , commonly known as Bill Joy, is an American computer scientist. Joy co-founded Sun Microsystems in 1982 along with Vinod Khosla, Scott McNealy and Andy Bechtolsheim, and served as chief scientist at the company until 2003...
originally wrote the C shell.
Similarly, the use of the HJKL keys for moving the cursor in the vi
Vi
vi is a screen-oriented text editor originally created for the Unix operating system. The portable subset of the behavior of vi and programs based on it, and the ex editor language supported within these programs, is described by the Single Unix Specification and POSIX.The original code for vi...
editor and its descendants also stems from the ADM-3A; it had the cursor-movement arrows printed on those four keys.
Both the arrows and the "home" correspond to the functions of the corresponding control characters Ctrl-H, Ctrl-J, Ctrl-K, Ctrl-L, and Ctrl-^ (identical to Ctrl-~) when sent to the terminal, moving the cursor left, down, up, right, and to the "home" position in the upper left-hand corner of the terminal, respectively. (The Ctrl-H and Ctrl-J functions were standard, but the interpretations of Ctrl-K, Ctrl-L, and Ctrl-^ were unique to the ADM-3A.)
Finally, the control key
Control key
In computing, a Control key is a modifier key which, when pressed in conjunction with another key, will perform a special operation ; similar to the Shift key, the Control key rarely performs any function when pressed by itself...
was located above, not below, the shift key
Shift key
The shift key is a modifier key on a keyboard, used to type capital letters and other alternate "upper" characters. There are typically two shift keys, on the left and right sides of the row below the home row...
-- in the same place where most modern PC keyboards put the Caps Lock key. Many standard Unix key combinations were designed with the QWERTY layout and the ADM-3A's original Ctrl key placement in mind. Many of those key combinations are still in use today, even on non-Unix operating systems. Seasoned computer users familiar with the original layout often claim that the different position of the Ctrl key on modern PC keyboard layouts makes the use of Ctrl key combinations more cumbersome. Solutions exist for many operating systems to switch around the Caps Lock and Ctrl keys in software, thus making the PC keyboard layout more closely resemble the ADM-3A's keyboard layout.