4164/41256 RAM Modification: Difference between revisions
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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). | 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 | == Pinout Comparison == | ||
Here is a comparison in pinout: | Here is a comparison in pinout: | ||
Revision as of 04:07, 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:
