The Apple II self test was first introduced with the enhanced Apple IIe and was later added to the Apple //c starting from the Unidisk 3.5 version (ROM 0).

Starting the test

To start the test both the closed and the open Apple keys must be pressed during boot. It is also possible to press the closed apple while pressing the CONTROL-OPEN APPLE-RESET keys to start the test at any time.

The test is also performed automatically if the keyboard is detached when the computer boots.

Tests performed

Following components are tested:

  • Main RAM and aux. RAM.
  • MMU
  • IOU
  • GLU

If a problem is detected at any point of the test sequence the test stops and a failure message is displayed.

Interpreting the results

If the MMU, IOU or the GLU are detected as faulty, the corresponding component name is displayed. RAM Chips are tested sequentially starting with the least significant bit of main RAM and working through the most significant bit. Then the auxiliary RAM is tested.

A RAM fault is shown as a 1 in a series of zeroes. The faulty RAM chip corresponds to the bit position of the 1. This means the rightmost number corresponds to the memory chip labeled as MDR0 for the main RAM.

A fault on the auxiliary RAM is indicated with an asterisk. A fault on the first 255 bytes of ram is additionally marked with a ZP which stands for zero pointer.

When the test is finished a SYSTEM OK message appears. On the Apple //c plus some garbled characters can be shown. This is no sign of malfunction.

Main Memory Failure