System speakers
The PC loudspeaker is the standard sound output in IBM-compatible PCs , its built-in loudspeaker. Before sound cards became popular around 1990 , it was the only way to generate tones and sounds on a PC.
functionality
Its control logic provides only two states: on and off, which corresponds to two different positions of the membrane. This means that the loudspeaker can normally only reproduce square waves. It can be controlled by the software in two ways: A frequency can be entered in the interrupt timer (PIT), which then automatically switches the loudspeaker on and off at this frequency until it is deactivated again. Alternatively, the speaker membrane can be explicitly set to one of the two states “tense” or “loose” via the keyboard controller . A volume control for the system loudspeaker is not provided on most PCs. The connection via interrupt timer and keyboard controller, which is strange by today's standards, was used on the first IBM PC to save chips and was later retained for reasons of compatibility.
Advanced sound generation
In order to be able to output natural sounds, other waveforms than rectangles, polyphonic music or quieter sounds on the PC loudspeaker, various programmers have tried to simulate a D / A converter with a counting method using software . For this purpose, the signal to be output was dithered and the loudspeaker was switched on and off by the CPU at exactly the right time using a timer interrupt. The disturbances should be in the ultrasonic range and should be smoothed to intermediate stages by the inertia of the membrane (see diagram). In practice, however, this process was either so computationally intensive that the computer could not perform any other tasks while the sound was being output (such as changing the displayed image content or querying input devices), or the pulse-width-modulated signal was audible as an annoying beeping sound. Furthermore, the timer interrupt could often not be executed at exactly the right moment due to the presence of other interrupts, which led to loud cracking. Nevertheless, such techniques were often used in early computer games for PCs, as the only alternative was to avoid such sounds entirely.
Due to their complex timing, these programs often only work correctly on PCs with a very specific CPU speed; on significantly faster PCs, the sounds that can be heard are usually no longer the desired ones. The quality is therefore much worse than with a Covox connector .
Modern emulators for older PC software, such as DOSBox , can output the corresponding sounds quite well through the external speakers. They usually do not support the real system loudspeaker because of the technical problems associated with modern operating systems (see below).
Todays use
BIOS
Many BIOS use the option of displaying error messages by means of beeps . This is helpful for troubleshooting computers that no longer start, on which often no image output and therefore no display of error messages via the graphics card on the screen is possible.
Portable devices
In most notebooks , the system loudspeaker signal is passed on to the built-in sound card and thus goes to the normal loudspeakers, but with some laptops the system loudspeaker is saved without replacement. In the case of motherboards with an onboard sound card, it is sometimes also possible to route the system loudspeaker signal to the same external loudspeakers that are responsible for outputting the sound card sounds.
Through programs
Up until a few years ago, various programs still made use of the simple option of playing advisory tones via the system loudspeaker even if the external loudspeakers were missing or switched off, e.g. B. Skype or the IRC program XChat notified the user about an incoming call or a chat request. However, Microsoft operating systems as of Windows Vista application programs no longer offer access to the real system loudspeaker; such access is now redirected to the sound card and thus - if available and switched on - to the external loudspeakers. Microsoft justifies this with the fact that the system loudspeaker is out of date. The only way to access the system speaker on these operating systems is to use an unsigned driver, but this creates a number of new problems. On Linux systems, the use of the system loudspeaker for simple beeps is generally still possible today, but not for the complex sounds described above, as the corresponding time-critical methods can hardly be integrated into a modern multitasking operating system without real-time design.
programming
The command is putchar('\a');sufficient in C code when using the console output to output an “ A lert” ( borrowed from the English alert , for “alarm”), which used to be (with Microsoft to Windows XP) usually in the form of a beep from the system loudspeaker was realized.