IBM 5150 - BIOS upgrade on 16KB-64KB motherboard - SW2 example


When upgrading the BIOS on a 16KB-64KB motherboard to the 10/27/82 one, the setting of switch 5 on motherboard switch block SW2 needs to be changed in most cases.
The following is an example - 128 KB of RAM.

	SW2-1	SW2-2	SW2-3	SW2-4	SW2-5	SW2-6	SW2-7	SW2-8	Comment
04/24/81 BIOS	ON	OFF	ON	ON	OFF	OFF	OFF	OFF	See note 1 below
10/19/81 BIOS	ON	OFF	ON	ON	OFF	OFF	OFF	OFF	See note 1 below
10/27/82 BIOS	ON	OFF	ON	ON	ON	OFF	OFF	OFF

To see if you need to change the setting of switch 5 on switch block SW2, refer to the settings diagram at here.
Of the two large columns in that diagram, the column on the right is the one to refer to, i.e. the one applicable to the 10/27/82 BIOS.

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Note 1

The 04/24/81 and 10/19/81 dated BIOS' only inspect switches 1 though 4 on SW2. Even so, at the time, IBM instructed that switches 5 to 8 be set to off. In the move to the 10/27/82 dated BIOS, the BIOS also inspects switch 5.