Which memory module first operated at the same speed as the motherboard bus?

Synchronous RAM (SDRAM) is the memory module that first operated at the same speed as the motherboard bus. This type of RAM was designed to synchronize its operation with the bus clock, allowing for a more efficient data transfer between the RAM and the motherboard. This synchronization enables SDRAM to take advantage of the speed of the bus, which leads to improved performance. SDRAM is capable of providing data to the CPU at the same rate that the bus can process it, reducing latency and increasing overall system efficiency.

In contrast, other types of memory, such as Dynamic RAM (DRAM), do not synchronize with the bus clock, which can lead to delays in data transfer. Small Outline Dual In-line Memory Modules (SODIMMs) are simply a form factor of memory and can house various types of RAM including SDRAM. Dual Data Rate (DDR) memory is an evolution of SDRAM that improves speed by allowing data to be read on both the rising and falling edges of the clock cycle, but it fundamentally builds upon the principles established by SDRAM. Thus, SDRAM is the correct answer as it established the capability to operate synchronously with the motherboard bus.