DRAM

Built with capacitors.

Capacitors slowly leak charge, so they need to be recharged (refreshed) periodically.

• Needs constant refreshing to maintain data (refresh every 64 milliseconds)
• Less expensive
• Higher density
• Used for main system memory
• Slower than SRAM

#Generations

#DDR3

• Speed 2133 MB/s
• Peak 17 GB/s

old used 1.5Volt, new uses 1.34Volts

#DDR4

• Speed 3.2 GB/s
• Peak 25,6 GB/s

#DDR 5

• Speed 6,4 GB/s
• Peak 51.2 GB/s

#Configurations

#Ranks

“2R” means Dual Rank. The module has two ranks of memory. A rank is a set of DRAM chips that operate simultaneously. Each rank can be accessed independently.

Fewer the better → simpler memory configurations are generally more stable and have better compatibility.

#Banks

Refers to the internal organization of each DRAM chip “x8” means each chip outputs 8 bits at a time. Common alternatives are: x4 (4 bits) or x16 (16 bits).

Fewer banks generally means better stability and compatibility.

This affects how the memory controller interacts with the RAM.

#Same Type

All chips within a memory module (across all ranks) need to be of the same type and specifications:

#Timing Consistency

• All chips must operate at the same speed.
• Same latency timings (CAS, RAS, etc)
• Same refresh requirements

#Voltage Requirements

• All chips need to use the same operating voltage
• Mixed voltage chips could cause damage or instability.

#Manufacturing/Quality Control

• Memory manufacturers typically use identical chips from the same prodection batch

#Memory Controller Requirements

• The memory controller expects uniform behavior across all ranks.