3.5.1 DRAM Types

DDR RAM Types

• Dynamic Random Access Memory (DRAM) is the most common type of computer memory.
• DRAM processes one command and one 64-bit data set (word) per clock cycle.
• Original DRAM processed one command/word per rising edge of the clock cycle.
• DDR RAM (Double Data Rate RAM) doubles the data rate by processing one set of data on both rising and falling edges of each clock cycle (double pumping).

DDR RAM Ratings

• Speed is often represented in MHz (bus speed).
• MT/s (mega transfers per second) represents the effective transfer rate (DDR rating).
• DDR rating is calculated by doubling the bus clock speed.
• PC rating (bandwidth) is the amount of data transferred per second.
• PC rating is calculated by multiplying the DDR rating by 8 (8 bytes = 64 bits).
• PC rating value is typically rounded down/up for marketing purposes.

DDR RAM Types

• DDR1: Operated at 133-200 MHz (266-400 MT/s), 2.5V, 2100-3200 MB/s bandwidth.
• DDR2: Doubled DDR1 specs: 266-400 MHz (533-800 MT/s), 1.8V, 4200-6400 MB/s bandwidth. Added buffer for increased speed.
• DDR3: Doubled DDR2 specs: 533-800 MHz (1066-1600 MT/s), 1.5V, 8500-14900 MB/s bandwidth.
• DDR4: Doubled DDR3 data rate and power saving features: 1.2V, up to 64GB sticks, lower power consumption and cooler operation.
• DDR5: Doubled DDR4 data rate, lower voltage (1.1V), RAM-integrated power management with 32-bit split channels or 4 x 32-bit channels, and increased chip densities for up to 64GB sticks.

Physical Characteristics

• DDR has 184 pins, DDR2 has 240 pins.
• The notch positions differ between DDR types, providing easy distinction.
• DDR3 and DDR4 have 240 and 288 pins respectively.
• DDR5 has 288 pins.

Memory Form Factors

• DIMM (Dual In-Line Memory Module): Used in Desktop computers.
• SO-DIMM (Small Outline DIMM): Used in Laptops. Smaller size, same capacity.
• UniDIMM: Allows DDR3 and DDR4 in same slot, requires support from memory controller.

Multi-Channel Configurations

• Multi-channel configurations increase bandwidth by splitting workload over multiple memory controllers.
• A typical system has one memory controller.
• Multi-channel adds more memory controllers.
• Quad-channel setup allows up to eight RAM sticks.
• The use of dual, triple, or quad channels generally improves memory bandwidth by 5-15% (varies).
• Multi-channel configuration depends on the motherboard, not the RAM itself.
• Dual, triple, and quad channels are supported by DDR3, DDR4, and DDR5. DDR1 and DDR2 only support dual channel.