DRAM, 30 Pin SIMM, 72 Pin SIMM, or 168 Pin DIMM:
Random Access Memory (RAM) has progressed in technology and form. It's original from required the placement of individual chips into chip sockets, a process that often lead to mangled pins on the chips.
Then these chips were mounted on a little board called the Single In-line Memory Module (SIMM) with 30 connection points on the edge of the board that mated with 30 connections in the SIMM socket on the motherboard. However, these boards had to be installed four at a time. So if you wanted 16MB of RAM, you had to buy four 4MB SIMMs. And you had to choose between parity and non-parity, you could not mix them. Parity memory refers to an extra bit that was serviced by special chipsets and provided for data integrity (like error correction).
Then came 72 Pin SIMMs for the Pentium processors and we had to install these in pairs. These SIMMS come in Extended Data Out (EDO), parity, or non-parity flavors.
Today there is the Dual Inline Memory Module (DIMM) specification that calls for a 168 pins. These DIMMS come in Synchronous DRAM (SDRAM), PC100 (for the PII350 to the PIII550), PC133 (for the upcoming PIIIs), or EDO (PII300 and under) flavors and install one module at a time.
EDO:
Extended Data Out (EDO) RAM is faster than older RAM, some motherboards support this RAM and some do not. If you put EDO RAM in a motherboard that does not support it, get ready for some abnormal behavior.
Parity or Non-Parity:
The regular SIMMs came in two flavors, parity or non-parity, EDO is EDO, no parity issue there.
PERFORMANCE:
RAM is measured in access time, nano-seconds (ns) or one-billionths of a second, the smaller the better. An interesting note here, hard drive access times are listed in milliseconds (ms) or one thousandths of a second, RAM is 1 million times faster than a hard drive, no wonder that more RAM makes Windows faster.
EDO RAM was supposed to be standardized at 60ns, however, there is much of it that is 70ns, and there was one company that would sell 50ns EDO RAM. These were used for 66MHz bus speeds.
PC100 RAM is actually SDRAM used for the faster bus speeds (100MHz). And is designed for the 440BX chipset motherboards. There are 168 Pin SDRAMS that are non-PC100. These were for the TX and LX chipsets (66Mhz bus speeds). SDRAM was used as processor cache memory for the Pentium processors.
PC133 RAM is for the 133MHz bus speeds expected with the future PIII processors.
For detailed information, check out:
INSTALLATION:
|
|
|
|
SIMM |
DIMM |
 |
 |
DDR and DDR2.
Todays motherboards use Double Data Rate or DDR RAM. DDR is able to write and read in the same clock cycle doubling the bandwidth between the processor and the RAM. DDR2 doubles this again.
RAMBUS.RAMBUS memory was Intels attempt at cornering the RAM market with a serial specification. It failed miserably.
