The user has direct control over only one task, however. The user has direct control over the microcode and may rewrite it according to individual taste. The Alto has the interesting property of using software often microcode to perform many tasks, such as keyboard encoding and character generation, that are typically done in hardware.
This approach leaves the Alto with an occasionally cumbersome but highly flexible architecture. All of the Alto software can be retrieved from across the network. Photo 5a: Examples of Alto software: Display of the Alto Executive, with an example of star and question-mark notation. This program speaks to the user directly and makes facilities available for file manipulation and program execution. An interesting feature of the Executive is that of escape expansion and file-name completion.
Thisallows a programmer to name a file in a descriptive manner such as Gatewaylnformation. The Executive program will recognize it as soon as it has read enough characters to determine the file uniquely. By typing a question mark instead of an escape, the Executive will list all file names that are valid matches for the string typed thus far.
The Alto has a highly flexible and rugged file system. When a file name is entered for the first time, the file name is stored exactly as typed, even with regard to upper- and lowercase. Since the file names may be very long, this permits a programmer to use upper- and lowercase to improve readability. After the creationof a file, case is ignored when the user is speaking about the file, so either of the two names in the previous examples, as well as longfilename.
Alto files are divided into pages. Each page contains a small header that describes the current page, tells what file the page belongs to, and points to the places on the disk that contain the next and previous pages for the same file. This makes the file system almost indestructible. A program called Scavenger can automatically rebuild a broken file system.
Of course, no Alto is an island, so software is needed to deal with the Ethernet network. Some of this software appears in the form of the NetExecutive see photo 5b and FTP file-transfer program. The NetExecis a program that appears to be very similar to the Alto Executive, but it loads programs from across the network rather than from the local disk. This means that a user need not keep infrequently used or large programs locally.
Instead, these programs can be loaded through the network at an apparent speed of approximately , bits per second only when needed. FTP performs similar feats of file manipulation, but in a considerably more flexible manner.
Photo 5c: Examples of Alto software: Typical Mesa program being edited by Bravo; note the different typefonts used in the program listing. Although a great deal of software written for the Alto is in BCPL, there is a new contender for software development called Mesa. Mesa is a Pascal-like language that is incompatible with BCPL because of differences in their respective microcodes. Mesa is expected to be the programming language for the successors of the Alto see photo 5c.
BCPL and Mesa are the system languages for the Alto, which means that the system utilities and many applications programs are written in them. Other languages are available on the Alto, however. Much of the research work done on the Alto at Xerox is written in Smalltalk, an object-oriented language that is both easy to learn and highly powerful see the special August BYTE issueon the Smalltalk language. Another supported language is LISP, a list-processing language that is very popular in the artificial intelligence research community.
Photo 5d: Examples of Alto software: Directory from the Neptune directory editor. The file names in black have been selected for further operations such as printing or erasure. The cursor is displayed as a cross in a circle. A system with the advanced graphics capability of the Alto will make extensive use of those facilities. The screen may be broken up into windows, and each window may be accessed in a different manner, ifdesired.
Many Alto programs use only the mouse and screen windows for program control. A file may be deleted simply by touching the file name with the cursor, then touching the Delete spot on the screen with the cursor.
As the cursor enters a new window, it may change shape, perhaps appearing as an arrow in one window and a paintbrush in another.
The document in the bottom window has to been converted to the form shown in the top window. Since the Alto is used extensively for research in the office automation field, a good text editor is an obvious requirement.
Bravo is a text editor and formatter widely used on the Alto. Bravo is controlled partly by keyboard commands and partly by mouse commands. It allows a user to open windows into one or more files. Text may be added or deleted by pointing at the desired location on the screen see photo 5e with the mouse cursor, and giving a command via the keyboard or mouse.
Bravo supports many different fonts and allows the user to change easily from one font to the next. In addition, Bravo remembers the changes that have been made to a document and allows the user to reverse any or all changes. Bravo allows the user to edit and format text, but often a person may wish to include illustrations in a document. To do this, a program called Draw is used. Draw is an interactive sketch-pad program that provides a variety of tools for creating and manipulating pictures made from lines, curves, and text.
Draw divides the screen into a number of windows see photo 6. The left side of the screen contains a menu of commands and a variety of brushstrokes that can be selected. The top of the screen contains an area for text commands and messages from the program. The middle of the screen is the picture workspace. Curves can be drawn by moving the cursor directly, or by selecting several points and allowing Draw to mathematically fit a curve to those points.
Once an object is defined, it can be repainted using a number of brushstrokes. Since this is very similar to the techniques used by artists and calligraphers, quite a bit of artistic expression is possible. An object can be duplicated, rotated, stretched, or shrunk, by means of a small set of commands and mouse gestures.
Photo 6a: Use of the Draw program: Points are placed with the cursor, and curves and lines are filled in by the program.
Photo 6c: Use of the Draw program: Texture is given to the lines; dotted lines are created with the scissors cursor. Photo 6d: Use of the Draw program: Picture may be mathematically manipulated; a new figure may be created by reversing, tilting, or stretching a copy of the original. Each Alto is assigned an Ethernet address that identifies it uniquely onthe network.
A typical Ethernet address might be 50 , which is meaningless to most people. Since opening at the end of , over 5, children have visited the Centre. These children deserve a space which is engaging and instructive, where they can feel a sense of adventure, exploration and surprise!
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