Some of them used                ctrl alt +    for turbo on and       ctrl  alt -     for turbo off.

The +/- keys on number pad.

Tom

Dell doesn't hide or otherwise destroy old manuals like HP and others do.

I don't see anything about a turbo Mode.  The 8088 systems had that.

The system clock is usually a rectangular fixed frequency Ocillator

The bus speed always runs at the same speed at which the processor is running. If the processor is running at 12 MHz, the bus speed is also at 12 MHz.

Select Product By Model > Desktops > 286 System > PCs Limited 286-X

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http://support.dell.com/support/edocs/dta/286_X/

PC's Limited 286-x

Switch Position Function 
 

1         On           Using a color monitor as the primary display.                          
                                                                                              

          Off*         Using a monochrome monitor as the primary display.                     
                                                                                              

2         On           Green LED on SmartVu� is a speed indicator.                            
                                                                                              

          Off*         Green LED on SmartVu is power-on indicator.                            
                                                                                              

3         On*          256-KB ROM chips.                                                      
                                                                                              

          Off          128-KB ROM chips.                                                      
                                                                                              

4         On           Maintenance mode (used during manufacturing).                          
                                                                                              

          Off*         Operation mode (normal mode).                                          
                                                                                              

5         Off*         Reserved.                                                              
                                                                                              

*Indicates default setting
With Switches 7 & 8 both OFF (1024 KB):

6       Off        512-KB base (512 KB extended).               
                                                                

        On*        640-KB base (384 KB extended).               
                                                                

*Indicates default setting

With 6 OFF:

RAM 256 KB 512 KB 640 KB 1024 KB Split 
 

7         On          On          Off       Off*                
                                                                

8         On          Off         On        Off*                
                                                                

*Indicates default setting

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Regrettably, there is no single jumper on the front of the motherboard to put it in Turbo mode.  There are jumper sets for the battery, speaker, and keylock.  Instead, there is a group of 10 sets of prongs that come out of the motherboard and bend to the front.  Next to one end of the set is J6 DIAG.  I tried jumpering each of the 10 sets, one at a time, with no speed increase.  Some sets caused the computer not to start, while two others caused it to beep.

Bob Boyd

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Correction, the PC's Ltd Turbo-PC did have a Dip switch Speed setting where Turbo mode could always be invoked.