View source for 4164/41256 RAM Modification

'''Williams MPU'''s shipped with 24 × [[wikipedia:Mostek|Mostek]] '''4116''' DRAM (16,384 × 1-bit), introduced in 1977 — only a few years before Defender.

[[File:4116_Pinout.jpg|thumb|400px|4116 pinout]]

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:

[[File:Ram_Comparison.png|center|800px|4116 vs 4164 vs 41256 pinout]]

== Modify the MPU ==
Original MPU Power Connector Pinout

[[File:MPU_Unmod_Power_-_Noted.png|center|800px|Original MPU Power Connector Pinout]]

== See also ==
* [[Hardware - General]]
* [[Battery Damage]]