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IBM 5160:  RAM on a '64 - 256KB' Type of Motherboard





4 banks of 64 KB motherboard RAM, providing up to 256 KB of conventional memory.

RAM chips of type 4164 are used, of an access time rating of 200 ns (or faster), and of the type where pin 1 is not used (Not Connected).  4164 examples.
200 ns is the figure that appears in IBM's technical reference for the 5160.

Bank 0:	64 KB sized,	addressed 00000 to 0FFFF hex	(    0 KB to   64 KB)   (socketed)
Bank 1:	64 KB sized,	addressed 10000 to 1FFFF hex	(  64 KB to 128 KB)   (socketed)
Bank 2:	64 KB sized,	addressed 20000 to 2FFFF hex	(128 KB to 192 KB)   (socketed)
Bank 3:	64 KB sized,	addressed 30000 to 3FFFF hex	(192 KB to 256 KB)   (socketed)

Click here for a diagram that shows the bank and bit layout on the 5160 motherboard.


RAM related switch settings on motherboard

On IBM 5160 motherboards, switches 3 and 4 on switch block SW1 selectively disable/enable the RAM banks.
The settings are at here.


Increasing conventional memory

First, click here for a definition of 'conventional memory'.

Normally, but not mandatory for the IBM 5160, you would fully populate the motherboard RAM banks before adding more conventional memory via expansion cards.  An example is shown here.

However, in the IBM 5160, you have the option of adding expansion card based conventional memory without having to first populate all of the motherboard RAM banks.  An example is shown here.

See also the '640K of motherboard RAM' section below.


Design flaw

Be aware of a design flaw, one that affects the 5160's ability to determine how much conventional memory is fitted (on motherboard + on expansion cards).
The flaw is discussed at here.


POST test of conventional memory

During the 5160's Power-On Self Test (POST), the POST tests the conventional memory (the amount that it thinks is fitted).

If a problem is found in the first 16 KB (assumption: 11/08/82 BIOS), the POST will halt.  It will appear to you that the motherboard is 'dead'.  For further information, see the section below titled 'Failure of first 16 KB'.

If a problem is found in the remaining RAM, a 201 type error is reported on-screen.  The format of a 201 error produced by a 5160 is "aaaaa bb 201".  An example is "20000 80 201".
The "aaaaa" portion indicates which address the fault is at.
The "bb" portion indicates which bit/s is/are faulty.

Note however, that because of the design flaw discussed at here, you will not always see a 201 error if a RAM chip has failed (instead, seeing less RAM than fitted).

For a 201 error, you can use the diagram here to calculate the failing bit/s, and the address as a KB figure.

Click here for a diagram that shows the bank and bit layout on the 5160 motherboard.


640K of motherboard RAM

A modification is possible so that 640K of RAM can be fitted in the RAM sockets of the 64-256KB version of IBM 5160 motherboard.  <----- 5160, not 5150
In effect, it converts the 64-256KB motherboard to a 256-640KB one.
For more information, see note 1 at the bottom of here.


Failure of first 16 KB

If the POST (assumption: POST in 11/08/82 BIOS) discovers a problem in any of the first 16 KB of RAM, the POST will stop, providing no indication whatsoever (visual or audible).  To you, it will appear that the motherboard is 'dead'.

Note that the first 16 KB corresponds to the first quarter of each chip in bank 0 (64 KB sized).  RAM chips fail in different ways.  Therefore, if a RAM chip in bank 0 fails completely, you'll see the 'dead' motherboard symptom described earlier.  But if a RAM chip in bank 0 fails in such a way that the failure only affects an address/addresses in the last three quarters of the chip, then the BIOS will display a corresponding 201 error.