4164/41256 RAM Modification

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!

These chips require 3 voltages(Triple-Rail) to operate: +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.

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.

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). 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

Here is a comparison in pinout: