4164/41256 RAM Modification

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

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:

4116 vs 4164 vs 41256 pinout

Modify the MPU

Original MPU Power Pinout

See also

• Hardware - General
• Battery Damage