Dynamic RAM (DRAM) DRAM is a classic form of RAM and has since been replaced by the faster and less expensive SDRAM. DRAM stores data electrically in a storage cell and refreshes the storage cell every few milliseconds.
Extended Data-Out RAM (EDO RAM) EDO RAM is faster than DRAM. EDO RAM has also been replaced by SDRAM. EDO RAM is an improvement on DRAM because it has advanced timing features. EDO extends the amount of time data is stored and has a reduced refresh rate. This alleviates the CPU and RAM from timing constraints and improves performance.
Synchronous DRAM (SDRAM) SDRAM replaced DRAM, FPM, and EDO. SDRAM is an improvement because it synchronizes data transfer between the CPU and memory. SDRAM allows the CPU to process data while another process is being queued. Figure shows an SDRAM.
Double Data Rate SDRAM (DDR SDRAM) DDR SDRAM is a newer form of SDRAM that can theoretically improve memory clock speed to 200 megahertz (MHz) or more.
Chip specification DDR-200: DDR-SDRAM memory chips specified to run at 100 MHz DDR-266: DDR-SDRAM memory chips specified to run at 133 MHz DDR-333: DDR-SDRAM memory chips specified to run at 166 MHz DDR-400: DDR-SDRAM memory chips specified to run at 200 MHz
Stick/module specification PC-1600: DDR-SDRAM memory module specified to run at 100 MHz using DDR-200 chips, 1.600 GByte/s bandwidth per channel. PC-2100: DDR-SDRAM memory module specified to run at 133 MHz using DDR-266 chips, 2.133 GByte/s bandwidth per channel PC-2700: DDR-SDRAM memory module specified to run at 166 MHz using DDR-333 chips, 2.667 GByte/s bandwidth per channel PC-3200: DDR-SDRAM memory module specified to run at 200 MHz using DDR-400 chips, 3.200 GByte/s bandwidth per channel.
DDR SDRAM DIMMs have 184 pins (as opposed to 168 pins on SDR SDRAM, or, 240 pins on DDR-2), and can be differentiated from SDRAM DIMMs by the number of notches (DDR SDRAM has one, SDR SDRAM has two). DDR operates at a voltage of 2.5 V, compared to 3.3 V for SDR SDRAM.
- The different pin configuration for DDR RAM Modules:
1. 172-pin MicroDIMM, used for DDR SDRAM
2. 184-pin DIMM, used for DDR SDRAM
3. 200-pin SO-DIMM, used for DDR SDRAM and DDR2 SDRAM
4. 204-pin SO-DIMM, used for DDR3 SDRAM
5. 214-pin MicroDIMM, used for DDR2 SDRAM
6. 240-pin DIMM, used for DDR2 SDRAM, DDR3 SDRAM and FB-DIMM DRAM
Single Inline Memory Module (SIMM) SIMM is a memory module with 72 or 30 pins, as shown in Figures and . SIMMs are considered legacy components and can be found in older machines. SIMMs with 72 pins can support 32-bit transfer rates and 32-pin SIMMs can support 16-bit transfer rates.
Dual Inline Memory Module (DIMM) DIMM is a memory module with 168 pins as shown in Figure . DIMMs are commonly used today and support 64-bit transfer.
Rambus Inline Memory Module (RIMM) RIMM is a 184-pin memory module that uses only the RDRAM, as illustrated in Figure . Smaller modules called SO-RIMM have a 160-pin connector. Some systems require that RIMM modules be added in identical pairs while others allow single RIMMs to be installed.