[DRAM Basic] What are the main types and specifications of RAM?

The dominant type of computer memory currently in use is the DDR (Double Data Rate) series, which comes in various forms and technical specifications.

• DDR Series: This refers to a type of Synchronous Dynamic Random-Access Memory (SDRAM) that can transfer data twice per clock cycle. As technology evolves, the primary specifications in the market are DDR4 and DDR5.
  • DDR4: Widely used in older platforms (e.g., Intel 11th Gen and earlier CPUs, AMD Ryzen 5000 series and earlier CPUs) and some current mid-to-low-end new platforms. Its clock speeds typically range from 2133 MHz to over 4800 MHz.
  • DDR5: The latest generation of memory technology, offering higher baseline clock speeds (starting at 4800 MHz, now reaching 8000 MHz and beyond), greater bandwidth, lower operating voltage, and higher single-module capacities. DDR5 introduces "on-die ECC" (Error-Correcting Code) for enhanced stability and integrates a PMIC (Power Management Integrated Circuit) directly onto the memory module. This shifts power management from the motherboard to the memory module itself, improving power efficiency and stability. DDR5 also features a 16n prefetch architecture, doubling DDR4's 8n prefetch, theoretically offering twice the bandwidth.
• DIMM (Dual In-line Memory Module):
  • This is the standard memory module used in desktop computers and servers. It has independent electrical contacts on both sides.
  • UDIMM (Unbuffered DIMM): Common for consumer desktop PCs.
  • RDIMM (Registered DIMM): Typically used in servers and workstations. These modules feature a register chip that buffers signals, improving memory stability and scalability for larger capacities, though often at a slightly higher latency and cost.
• SODIMM (Small Outline Dual In-line Memory Module):
  • These are smaller memory modules than DIMMs, primarily used in laptops, mini PCs, and some compact ITX motherboards.

Important Note: DDR4 and DDR5 memory modules have different physical designs, including key notch positions and pin counts. Therefore, DDR4 motherboards cannot install DDR5 memory, and vice versa. Always ensure you purchase the memory type supported by your CPU and motherboard.