Dual in-line memory module

A dual in-line memory module (DIMM) is a small circuit board carrying memory integrated circuits, with signal and power pins on both sides of the board, in contrast to a single in-line memory module (SIMM).

Description
The individual gold or lead connectors (pins) on SIMMs, although they are on both sides of the chip, are connected to the same memory chip, while on a DIMM, the connections on each side of the module connect to different chips. This allows for a wider data path, as more modules can be accessed at once. DIMM pins are arranged in a zigzag design to allow PCB tracks to pass between them.

The 8-byte DIMM format with dual-sided contacts can accommodate 4- and 16-megabit dynamic RAM chips, and is predicted to handle 64- and 256-Mbit devices. The 8-byte DIMM will hold up to 32 megabytes of memory using 16-Mbit DRAMs, but with the 256-Mbit future-generation DRAM, it will be able to hold a 64-Mx64 configuration. Another variation, the 72-pin, is designed to connect directly to 32-bit data buses, and is intended for use in memory-expansion applications in notebook computers.

A dual in-line memory module (DIMM), as opposed to SIMMs (previously used by the majority of the PC industry) allowed for a 128-bit data path by interleaving memory on alternating memory access cycles. SIMMs on the other hand, have a 64-bit data path. Suppliers universally agreed that the DIMM would eventually replace the SIMM as the market's preferred memory module.

History
The Power Macintosh 9500, introduced in June 1995, was the first model from Apple Computer to use 168-pin DIMM slots for memory upgrades, in contrast to earlier models which used SIMMs. With the introduction of the MacBook Air in January 2008, Apple began soldering RAM directly to the logic boards of its models to make them more compact, at the expense of making user upgrades impractical. Starting with Macs using the Apple M1 in November 2020, the memory was directly incorporated onto the package with the processor.