Classic Computer Magazine Archive COMPUTE! ISSUE 89 / OCTOBER 1987 / PAGE 60


Sheldon Leemon

Behind The Workbench

Often, you can tell the level of a user's experience by the kinds of questions he asks. Someone who's worked with the Amiga for a while might say that he's having trouble loading a certain program, while an absolute beginner will complain, "I can't get into this disk." It's usually not too hard to figure out his problem, but the way he has stated it shows that he really doesn't have any concept of how files are stored on a disk or how you find out information about these files.

Part of the problem is that the Workbench makes it so easy to operate the computer using the mouse and icons that most of the time the user doesn't have to worry about what's really happening when he moves those pictures. So the first time he comes across a program disk with no icons on it at all, his natural reaction is, "What do I do now?" At that point, harsh reality can no longer be hidden behind pretty pictures. It's time to sit down and have that difficult talk about the bits and the bytes.

Storage In Files

A 3½-inch Amiga disk holds over 900,000 characters of information, but letters and numbers aren't stored on the disk randomly. Instead, information is stored in named files, which are made up of related alphabetic or numeric characters, or of computer instructions. For example, all of the computer instructions that make up a word-processing program are stored in a single program file. If you use the word processor to create and save a document to disk, all of the characters that make up the document are stored in a single data file.

A file has a number of attributes, such as its name, size, and so on. To find out this information, you need a special type of program. The Workbench program, for example, displays some files as icons. The name of the file appears below the icon, and you can find out additional information by highlighting the icon and using the Show Info menu item. The Workbench program only displays icons for certain types of files, however (as we saw in the August column). Therefore, you must use another type of program to find information about the rest of the files.

One such program is called the CLI (Command Line Interface). You can find the icon for this program in the System drawer on the Workbench disk (but only if you remember to turn the CLI switch on the Preference screen to ON). When you start the CLI program, all you'll see is an empty window with this prompt: 1>. This means the program is waiting for you to type a command. If you type the DIR command, you'll get a list of all of the files in the current directory. Type DIR OPT A, and you'll get a list of all of the files in each sub-directory as well. To list all of the files on an external disk drive, you could type DIR OPT A. There are a lot of other CLI commands, and they are discussed in depth in books like COMPUTE!'s AmigaDOS Reference Guide. But the DIR command is enough to let you start looking at disk filenames.

Programs That Help

Although the CLI program is included with every Amiga, it's harder to use than the Workbench, since it requires you to remember a lot of commands. Several intermediate programs are available that combine the power of the CLI with the ease of use of the Workbench. For example, there are public domain programs like DirUtil, which let you display the list of files on a disk in a scrolling window. These programs may be found on bulletin board services, commercial information services like CompuServe and GEnie, and in collections of public domain software like the one put together by Fred Fish. There are also some commercial programs that provide even more elaborate functions, such as CLI Mate and Zing.

Once you've used the CLI DIR command, or one of the other programs described above, you'll soon find out that there can be hundreds of different files on a disk. Some are program files, but many are data files. A data file is just a collection of information, like a word processing document, or a picture from a paint program. You can't run these files, since they don't contain computer instructions like a program does. Data files are helpful only when used in conjunction with a program that knows what to do with them. How can you find out what a particular file does? One way is to try and run that file. If you type in the filename at the CLI prompt, the CLI will try to run the program. If you get back a message that says that it was not an object module, you'll know that it's a data file, and not a program.

Another way to tell is to pay close attention to the name. For example, sometimes, data file names will end in a string of characters that indicate which program will run them, such as pic for a picture file, or bas for a BASIC program file. And, files named Readme, Manual, or that end in the characters .doc or .txt will usually contain text, often instructions on how to run the program. To read these files, use the CLI TYPE command (TYPE Readme, for example), or load them into your favorite word processor. If you look at the instructions first, you'll often find an explanation of what some of the other files are for, as well.