3.5.1 DRAM Types

Learn the different types of RAM that can be installed on a PC system.

Properties

• Speed (in megahertz, MHz)
• DDR Rating (in megatransfers/second, MT/s) calculated by doubling the RAM's bus clock speed; e.g. DDR-226 133MHz * 2 => 226MT/s

Static RAM (SRAM)

Stores data using four transistors for every bit of data, and it doesn't require constant power to maintain the contents of memory.

• more complex, less storage density than DRAM
• faster, requires less power than DRAM
• Regular SRAM requires periodic power to maintain memory state
  • refresh late is less than that of DRAM
  • Non-Volatile SRAM (nvSRAM) can maintain memory state without power

Dynamic RAM (DRAM)

The most common type of memory. It processes one command per clock cycle and one 64-bit set of data, called a word. DDR RAM processes one set of data on both the rising and falling edge of each clock cycle, doubling the processing speed.

Synchronous DRAM modules slows it's own clock speed down to match that of the motherboard, while normal DRAM modules maintain it's own clock speed to go as fast as it can.

Each green intersection represents when a word is being processed.

Generations

Generation	Frequency / Clock Speed (MHz)	Rating (MT/s)	Voltage	Bandwidth (MBs)	Capacity (GB)
DDR1	133-200	226-400	2.5	2100-3200	1
DDR2	266-400	533-800	1.8	4200-6400	8
DDR3	533-800	1066-1600	1.5	8500-14900	16
DDR4	1066-1600	2132-3200	1.2	12800 - 25600	64
DDR5	2132-3200 (not always true, DDR4 can have 3200 MHz)	4264-6400	1.1	38400 - 51200	128

Physical Characteristics

Generation	Pin Count	Picture
DDR	184
DDR2	240
DDR3	240
DDR4	288
DDR5	280

Form Factors

DIMM (any variation of DDR RAM)

• Typically installed on desktop systems, motherboards typically only have 4 module slots

SODIMM (smaller version of DIMM)

• Typically installed in smaller computer systems like laptops
• two pin counts, 144 and 200
  • 200 pin SODIMM used in DDR2 & DDR3\
  • 144 pin SODIMM used in SDRAM, DDR, and DDR2

Universal DIMM (motherboard upgrade)

• allows for DDR3 and DDR4 modules to be supported by the same slot when usually motherboard RAM slots only support one type of DDR

Multichannel Configurations

Typically, systems have a single memory configuration controller that handles all connected memory modules. All the data that needs to be sent to the RAM is sent through the controller acting as a middleman.

Multichannel configurations add additional memory controllers to the motherboard, allowing for more than the usual limit of 4 memory modules to be connected. They are then handled by additional memory controllers.

Usually, systems that have multichannel memory configurations are running dual or triple channel configurations experience a 5-15% increase in bandwidth.

Dual channel configurations are only supported by DDR Generations 2-5, and triple channel configurations are only supported by Generations 3-5.

Error-Correcting Code RAM (ECC RAM)

Uncommon type of Random-Access-Memory used in enterprise-level workloads and servers, and the average PC motherboard doesn't support it.

ECC RAM modules use a code to detect and correct data corruption for databases.

• cloud industries like finance
• reduced crashes, max system availability
• more expensive because of the extra memory chip that always checks for errors and corrects them
  • only works on single-bit errors
  • multiple-bit errors result in a system halt

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