IBM 5150 - 16KB-64KB motherboard - 04/24/81 and 10/19/81 BIOS'


Various versions of IBM DOS have a 'minimum RAM' requirement.

The tables below contain the results of attempting to boot IBM DOS in the following conditions:
 •  A 16KB-64KB type of IBM 5150 motherboard; and
 •  No RAM expansion card/s; and
 •  The motherboard fitted with either the 04/24/81 or 10/19/81 revision of BIOS; and
 •  Motherboard switch banks SW1 and SW2 set for 64 KB or less of RAM; and
 •  A cold boot (i.e. power switch turned on).

The 10/27/82 revision of BIOS was not included in these tests, because when that BIOS is fitted to a 16KB-64KB motherboard, a RAM related bug in the BIOS has an effect if SW1/SW2 are set to less than 64 KB.  The effect is that the POST within the BIOS miscalculates the amount of motherboard RAM, calculating that there is more motherboard RAM than actually fitted.


IBM DOS 1.00

04/24/81 or 10/19/81 BIOS.
Attempt to cold boot using an IBM DOS 1.00 boot floppy:

Motherboard
configured for		   Symptom / Result
16 KB RAM   'PARITY CHECK 1' on-screen, plus floppy drive access LED on continuously, plus floppy drive spindle turning continuously.    (See note 1 below.)
32 KB RAM   IBM DOS 1.00 booted successfully
48 KB RAM   IBM DOS 1.00 booted successfully
64 KB RAM   IBM DOS 1.00 booted successfully


IBM DOS 2.10

04/24/81 or 10/19/81 BIOS.
Attempt to cold boot using an IBM DOS 2.10 boot floppy:

Motherboard
configured for		   Symptom / Result
16 KB RAM   'PARITY CHECK 1' on-screen, plus floppy drive access LED on continuously, plus floppy drive spindle turning continuously.
32 KB RAM   Nothing on-screen except underline cursor.  Floppy drive access LED on continuously, plus floppy drive spindle turning continuously.
48 KB RAM   IBM DOS 2.10 booted successfully
64 KB RAM   IBM DOS 2.10 booted successfully


IBM DOS 3.10

04/24/81 or 10/19/81 BIOS.
Attempt to cold boot using an IBM DOS 3.10 boot floppy:

Motherboard
configured for		   Symptom / Result
16 KB RAM   'PARITY CHECK 1' on-screen, plus floppy drive access LED on continuously, plus floppy drive spindle turning continuously.
32 KB RAM   'PARITY CHECK 1' on-screen, plus floppy drive access LED on continuously, plus floppy drive spindle turning continuously.
48 KB RAM   'PARITY CHECK 1' on-screen, plus floppy drive access LED on continuously, plus floppy drive spindle turning continuously.
64 KB RAM   IBM DOS 3.10 booted successfully


IBM DOS 3.30

04/24/81 or 10/19/81 BIOS.
Attempt to cold boot using an IBM DOS 3.30 boot floppy:

Motherboard
configured for		   Symptom / Result
16 KB RAM   'PARITY CHECK 1' on-screen, plus floppy drive access LED on continuously, plus floppy drive spindle turning continuously.
32 KB RAM   'PARITY CHECK 1' on-screen, plus floppy drive access LED on continuously, plus floppy drive spindle turning continuously.
48 KB RAM   'PARITY CHECK 1' on-screen, plus floppy drive access LED on continuously, plus floppy drive spindle turning continuously.
64 KB RAM   'Configuration too large for memory' on-screen.




Note 1 There was a successful boot if all I did was simply populate the second RAM bank, leaving the motherboard switches set to 16 KB.