The Power On Self-Test (POST) is executed each time the computer is powered-up. The POST tests the following:

If all tests are completed successfully, one short beep will be heard from the loudspeaker in the system unit.

If more than one beep is heard, make a note of the sequence of beeps and refer to the table below to determine the cause of the error. As an example, the beep sequence '1-3-3' represents a single beep, followed by a group of three beeps, followed by another group of three beeps.

Beep Sequence	Error Description
1-1-1	No video card
1-1-3	CMOS RAM read/write test failure
1-1-4	BIOS ROM checksum failure
1-2-1	Programmable interval timer failure
1-2-2	DMA initialisation failure
1-2-3	DMA page register read/write failure
1-3-1	RAM refresh verification failure
1-3-3	1st 64K RAM chip data line failure (multi-bit)
1-3-4	1st 64K RAM chip data odd/even logic failure
1-4-1	1st 64K RAM chip address line failure
1-4-2	1st 64K RAM chip parity failure
2-1-1	1st 64K RAM chip data line failure
2-1-2	1st 64K RAM chip data line failure (bit 1)
2-1-3	1st 64K RAM chip data line failure (bit 2)
2-1-4	1st 64K RAM chip data line failure (bit 3)
2-2-1	1st 64K RAM chip data line failure (bit 4)
2-2-2	1st 64K RAM chip data line failure (bit 5)
2-2-3	1st 64K RAM chip data line failure (bit 6)
2-2-4	1st 64K RAM chip data line failure (bit 7)
2-3-1	1st 64K RAM chip data line failure (bit 8)
2-3-2	1st 64K RAM chip data line failure (bit 9)
2-3-3	1st 64K RAM chip data line failure (bit A)
2-3-4	1st 64K RAM chip data line failure (bit B)
2-4-1	1st 64K RAM chip data line failure (bit C)
2-4-2	1st 64K RAM chip data line failure (bit D)
2-4-3	1st 64K RAM chip data line failure (bit E)
2-4-4	1st 64K RAM chip data line failure (bit F)
3-1-1	Slave DMA register failure
3-1-2	Master DMA register failure
3-1-3	Master interrupt mask register failure
3-1-4	Slave interrupt mask register failure
3-2-4	Keyboard controller failure
3-3-4	Screen memory failure
3-4-1	Screen initialisation failure
3-4-2	Screen retrace test failure
4-2-1	Timer tick interrupt failure
4-2-2	Shutdown failure
4-2-3	Gate A20 failure
4-2-4	Unexpected interrupt in protected mode
4-3-1	RAM failure address 010000H to 0A0000H
4-3-3	Interval timer channel 2 fail
4-3-4	Time of day clock failure
4-4-1	Serial port test in progress or failure
4-4-2	Parallel port test in progress or failure
4-4-3	Maths co-processor test in progress or failure
There is also a group of error beep codes which are preceded by a lower frequency tone (signified below by 'L').
L-1-1-0	VGA failure
L-1-1-1	Video DAC failure
L-1-1-2	System board select failure
L-1-1-3	Extended CMOS RAM failure