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- All applications available to the user are listed in the index on the left hand window. Associated with each application is a key letter which can be used to select it in conjunction with the square key. If two applications have the same key letter then the application with the higher slot number will be preceded by a Z, or even two Z's, if there are three applications. The suspended applications window automatically gives the name of all suspended applications along with the time and date of suspension. If the application is running in an external card then the slot number will be placed in the card column to the right of the window. The 'Your Ref' column on the left of the window is a 15 character wide slot which the application can set. It is useful for distinguishing between different instantiations of the same application. Finally the user can kill off applications by placing the highlight bar over the appropriate application in the suspended applications window and entering <>KILL. Note that on the Index menu the kill command is a 'safe' one and so must be entered using its diamond sequence, and not via the menu.
- The Filer is a built in popdown for handling the RAM filing system. Each application is associated with a default device and directory. These are set when the application is started by looking at the default settings in the panel. When the filer is called from an application it will inherit these settings. If the settings are changed from within the filer, using 'Select Directory' and 'Select Device', then the application settings will be altered correspondingly. Further, it is possible for these settings to be changed by the application itself. The filer delivers mail to applications, which consists of the name of the last marked file. Mailboxing is the way in which Z88 applications can communicate with each other. Any application can put a piece of mail in the mail box and each piece of mail has a type associated with it. Applications expecting mail then look for specific mail types and if they are present can read the message. The internal applications PipeDream and the Diary can collect the filename the filer leaves in the mailbox, th us thus providing a very friendly way of finding documents and diaries. The Z88 currently only has two types of mail which are the name type, for filenames, and the date type, used by the Diary, Calendar and Alarm.
- The screen is accessed by the application by means of the screen driver. All the screen functions, apart from high resolution graphics, can be accessed by sending a series of codes to the screen device, which will normally be standard output. The screen driver sequences are constructed from an ASCII SOH character ($01) followed by a count character, indicating how many parameters follow, a mnemonic function code (eg. 'B' for bold text) and any other parameters. From the programmer's point of view the screen driver allows very complex screen displays (including simple windows) to be built up mainly by sending string constants to the display. High resolution graphics are accessed by using system calls. The basic display is up to 256 pixels (96 in an unexpanded machine) across and 64 pixels deep.
- The menu, topic, help system provides the application with a friendly user interface for practically no programming cost at all. All the menu commands and help pages are defined by a static data structure. The special key sequences which correspond to the commands on the menus, and operating the menus by hand (using the highlight bar) both have the effect of generating the same unique key code which is returned to the application. The programmer decides which commands should return which codes, inserts this in the data structure, and the operating system will then automatically generate all the menus and help pages, process the diamond and square sequences and any special keys (eg. TAB) and simply pass a key code back to the application. Also note that menu commands can be hidden, ie. not displayed, and safe which means they are displayed, but are not accessible through the menu, only through the key sequence. Hidden commands are used to build aliases, where two or more key combinations perform the same function.
- Each application must take care to look after any errors which occur. One particular error code which every application must deal with is the RC_QUIT code which is produced when the user uses <>KILL in the Index. In response to a KILL request the application must close all open channels and de-allocate all allocated memory before using a system call to close itself down.
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