## Chapter 20 – Channels, Streams, Drivers and Windows As we have seen thus far, *NextBASIC* can *read data* from the keyboard and controllers using **INPUT** and **INKEY$** and it can *write data* onto the display or a printer by using **PRINT** and **LPRINT**. However, these commands are really a form of shorthand designed to protect the user from some of the computer's more complex features. To the **PRINT** command, for example, there is no difference between the screen and the printer. **PRINT "Mikayla"** really means: *take the characters which make up the word **Mikayla** and send them somewhere else*. It's just convenient to use the screen most of the time. Likewise, **LPRINT** usually sends data to the printer. In fact, what these commands really do is to send data to one of a number of *channels*. ### Channels A *channel* is the pathway to the computer's input and output devices and on the ZX Spectrum Next, they are designated by a letter. These are: | Designator | Direction | Description | Default Streams | Default Status | |---|---|---|---|---| | k | Input/Output[^p206-1] | Keyboard | 0,1 | Open | | s | Output | Screen | 2 | Open | | p | Output | Printer | 3 | Open | | i | Input | File (input) | | Closed | | o | Output | File (output) | | Closed | | u | Input/Output | File (Update) | | Closed | | v | Input/Output | Variable | | Closed | | m | Input/Output | Memory | | Closed | | d | Depends | Driver | | Closed | | w | Input/Output | Windows | | Closed | | r | Internal | Internal Use only | N/A | Open | *Table 19 – NextBASIC channels* To access a *channel*, it must be open. Opening a *channel* makes it ready to receive or produce data. A *channel* is opened by connecting it to a *stream*. From *NextBASIC*, you would use a command like: ``` OPEN #4,"k" ``` which means *connect stream 4 to the keyboard channel*. As evidenced by the table above, if we go by the direction of data flow there are three types of *channels*: *Input*, *Output* and *Input/Output* (or *Update*). However, we can better classify channels by device type: We have *Screen*, *Keyboard*, *Printer*, *File*, *Memory*, *Variable*, *Windows* and *Driver channels*. Let's examine them according to the device type however, as this affects what types of commands we can use with them and how. The *Screen Channel* deals with everything that goes to the screen. It is the simplest of all channels and most of its characteristics have been covered in *Chapter 15* already. It is already opened and connected to *stream* **#2**. In fact you can substitute any **PRINT** command with **PRINT #2** and it will work in the exact same way as a regular **PRINT** command. [^p206-1]: *Outputting data to the keyboard might seem a bit peculiar, but once you consider that the computer uses the lower screen (like **INPUT** does) to display the characters, it becomes clear why.*