, a POST card
is a diagnostic tool that reports error codes produced by a POST
. They are used by technicians to troubleshoot computers that refuse to boot. The cards relay POST codes generated by the system, and the system must therefore have a working CPU and BIOS, in addition to whatever I/O interface the POST card relies on. Thus, POST cards cannot be used to diagnose the cause of e.g. a dead motherboard. POST cards are desirable in situations where video is not available; either because connecting a monitor is impractical, or because the point of failure occurs before the video subsystem can be initialized.
POST cards are inserted into an expansion slot, and are available in ISA, PCI and other variants.
The card reports a number, consisting of two hexadecimal digits, that is output to an I/O port by the BIOS while running the POST.
Reference tables covering different BIOSes are needed.
Some motherboards come with a built-in display to diagnose hardware problems. Most also report POST errors with audible beeps, if a PC speaker is attached.