4164/41256 RAM Modification: Difference between revisions

Latest revision as of 04:50, 12 September 2026

Williams MPUs shipped with 24 × Mostek 4116 DRAM (16,384 × 1-bit), introduced in 1977 — only a few years before Defender.

These chips need three voltages (triple-rail):

+5 V — TTL input/output buffers
+12 V — primary power
−5 V — substrate bias / shield

If −5 V drops while +5 and +12 are still present, the chip overheats and fails quickly.

That triple-rail requirement made the 4116 a weak link on these boards, especially as the linear supplies aged and the rails got noisy.

4164 First Successor

In the early 1980s the direct successor appeared: the 4164 (65,536 × 1-bit).

An internal bias generator supplies the −5 V, so the part runs from a single +5 V rail. Pins that used to carry the extra supplies became another address bit, which is how capacity went up. 4164s generally run cooler and tolerate supply variation better.

41256 Last 16-Pin Successor

By the late 1980s density had increased again. Using the last unused supply pin as another address line gave the 41256 (262,144 × 1-bit).

Pinout Comparison

Here is a comparison in pinout:

Modify the MPU

What we need to do: For the 4164/41256 to work, we need to accomplish a few things.

Remove the -5v from Pin 1
Remove the +12v from Pin 8
Substitute +5v on Pins 1 and 8 (If we left these unconnected/floating, the address value would randomly change
The goal is to have +5 on Pins: 1,8 and 9. Ground stays on Pin 16

Original MPU Power Connector Pinout

Step 1 — Cut pins 5(+12 Regulated) and 9(-5v) * Keep one of the cut off pins *

Note - The 'Polarizing Key is on Pin 4. With the mod, if the connector is reversed/flipped it can't be plugged in *
Note - Pin 1 is on the right and Pin 9 is on the left *

@@ Line 1: / Line 1: @@
-Williams MPU's shipped with 24, 4116 DRAM (Dynamic Random Access Memory). These memories are 16k(16,384 x 1-bit)each. They were released by Mostek in 1977 (only a few years before Defender released!
+'''Williams MPU'''s shipped with 24 × [[wikipedia:Mostek|Mostek]] '''4116''' DRAM (16,384 × 1-bit), introduced in 1977 — only a few years before Defender.
-These chips require 3 voltages(Triple-Rail) to operate:
+[[File:4116_Pinout.jpg|thumb|400px|4116 pinout]]
-+5 provides the buffers for inputs and outputs to operate at TTL
-+12 primary power source
--5 used as a shield on the substrate to stabilize functionality
-If the -5v drops for any reason while the other 2 voltages are present, the result will be chip overheating and failure in a short time.
+These chips need three voltages (triple-rail):
-Due to these requirements, the 4116 has been a 'weak link' on these boards, especially as the linear power supplies age and the voltage becomes more unstable.
+* '''+5 V''' — TTL input/output buffers
+* '''+12 V''' — primary power
+* '''−5 V''' — substrate bias / shield
-In the early 80's some advancements in chip manufacturing were developed and the direct successor for the 4116 was made; the 4164 64 Kilobits (65,536 x 1-bit).
+If '''−5 V''' drops while +5 and +12 are still present, the chip overheats and fails quickly.
-By using an internal bias generator(for the -5v), the chip was able to operate on a single +5v supply. By freeing up pins once used by the other power sources, they were able to increase the address range(by one bit) and capacity! These tend to run cooler and are more forgiving to variations in supply voltage
-By the late 80's, they were able to pack more space in the chip and utilizing the last unused supply pin, they added another address line and increased the size to 256 Kilobits (262,144 x 1-bit). This is the 41256
+That triple-rail requirement made the 4116 a weak link on these boards, especially as the linear supplies aged and the rails got noisy.
+== 4164 First Successor ==
+In the early 1980s the direct successor appeared: the '''4164''' (65,536 × 1-bit).
+An internal bias generator supplies the −5 V, so the part runs from a '''single +5 V''' rail. Pins that used to carry the extra supplies became another address bit, which is how capacity went up. 4164s generally run cooler and tolerate supply variation better.
+== 41256 Last 16-Pin Successor ==
+By the late 1980s density had increased again. Using the last unused supply pin as another address line gave the '''41256''' (262,144 × 1-bit).
+== Pinout Comparison ==
 Here is a comparison in pinout:
+[[File:Ram_Comparison.png|center|800px|4116 vs 4164 vs 41256 pinout]]
+== Modify the MPU ==
+What we need to do: For the 4164/41256 to work, we need to accomplish a few things.
+* '''Remove the -5v from Pin 1'''
+* '''Remove the +12v from Pin 8'''
+* '''Substitute +5v on Pins 1 and 8 (If we left these unconnected/floating, the address value would randomly change'''
+* '''The goal is to have +5 on Pins: 1,8 and 9. Ground stays on Pin 16
+Original MPU Power Connector Pinout
+[[File:MPU_Unmod_Power_-_Noted.png|center|800px|Original MPU Power Connector Pinout]]
+'''Step 1''' — Cut pins 5(+12 Regulated) and 9(-5v) * Keep one of the cut off pins *
+* Note - The 'Polarizing Key is on Pin 4. With the mod, if the connector is reversed/flipped it can't be plugged in *
+* Note - Pin 1 is on the right and Pin 9 is on the left *
+[[File:Modified_Power_Connector.jpg|center|800px|Pins 5 and 9 cut]]
+== See also ==
+* [[Hardware - General]]
+* [[Battery Damage]]

Braedel (talk | contribs)

Latest revision as of 04:50, 12 September 2026

4164 First Successor

41256 Last 16-Pin Successor

Pinout Comparison

Modify the MPU

See also