Memory Modules

Early computers had RAM installed on the motherboard as individual chips. The individual memory chips, called dual in-line package (DIP) chips , were difficult to install and often became loose. To solve this problem, designers soldered the memory chips on a special circuit board to create a memory module.

Note

Memory modules can be single sided or double sided. Single-sided memory modules contain RAM only on one side of the module. Double-sided memory modules contain RAM on both sides.

DIP Dual in-line package is an individual memory chip. A DIP has dual rows of pins used to attach it to the motherboard.

SIMM Single in-line memory module is a small circuit board that holds several memory chips. SIMMs have 30-pin or 72-pin configurations.

DIMM Dual in-line memory module is a circuit board that holds SDRAM, DDR SDRAM, DDR2 SDRAM, and DDR3 SDRAM chips. There are 168- pin SDRAM DIMMs, 184-pin DDR DIMMs, and 240-pin DDR2 and DDR3 DIMMs.

RIMM Rambus in-line memory module is a circuit board that holds RDRAM chips. A typical RIMM has a 184-pin configuration.

SODIMM Small outline DIMM has a 72-pin and 100-pin configurations for support of 32-bit transfers or 144-pin, 200-pin, and 204-pin configurations for support of 64-bit transfers. This smaller, more condensed version of DIMM provides random-access data storage that is ideal for use in laptops, printers, and other devices where conserving space is desirable. The speed of memory has a direct impact on how much data a processor can process because faster memory improves the performance of the processor. As processor speed increases, memory speed must also increase. For example, single-channel memory can transfer data at 64 bits per clock cycle. Dual-channel memory increases the speed by using a second channel of memory, creating a data transfer rate of 128 bits. DDR technology doubles the maximum bandwidth of SDRAM. DDR2 offers faster performance and uses less energy. DDR3 operates at even higher speeds than DDR2. However, none of these DDR technologies are backward or forward compatible. Table 15 shows many common memory types and speeds.

Table 1-5 Common Memory Types and Characteristics 

Memory Type Industry Name Peak Transfer Rate Front Side Bus

PC100 SDRAM PC-100 800 MB/s 100 MHz
PC133 SDRAM PC-133 1060 MB/s 133 MHz
DDR-333 PC-2700 2700 MB/s 166 MHz
DDR-400 PC-3200 3200 MB/s 200 MHz
DDR2-667 PC2-5300 5333 MB/s 667 MHz
DDR2-800 PC2-6400 6400 MB/s 400 MHz
DDR3-1333 PC3-10600 10667 MB/s 1333 MHz
DDR3-1600 PC3-12800 12800 MB/s 1600 MHz
DDR3-1866 PC3-14900 14933 MB/s 1867 MHz
DDR3-2133 PC3-17000 17066 MB/s 2133 MHz

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