parallel presence detect (PPD)

Also see PPD file (Postscript Printer Description file).

Parallel presence detect (PPD) is a method of using resistor s to communicate a memory module 's speed and density to the basic input/output system ( BIOS ) when a computer boots (starts or restarts). The BIOS uses this information to configure the memory modules to run correctly or to detect if an incorrect memory module has been installed. Today, serial presence detect ( SPD ) is used on newer memory modules because SPD can store up to 400 times more information than PPD. PPD is used with 30- and 72- pin SIMM s.

PPD indicates the memory module's specifications using parallel pins on the module that transmit a binary code. If a pin has a resistor connected to it, it's a logical zero. If a pin does not have a resistor connected to it, it's a logical one. The combination of resistors connected and not connected make up the binary code that the BIOS uses.