How to Visually Identify Your Memory
And we added a sprinkle of some very basic memory facts!

During the early part of the 1980's personal computer memory primarily of memory chips in dual in-line packages that were either soldered to the printed circuit boards or pressed into DIP sockets. Both of these memory types were extremely difficult to upgrade or even repair, and beyond that, they took up enormous amounts of space on the printed circuit board. Because of these problems as well as the need to improve performance, new developments such as memory expansion cards began to surface. While these were the true grandfathers of modulization, they provide to be only a temporary solution, as the I/O bus performance quickly became an impediment to what was believed to be the "high speed memory devices of that era.

The first true memory module was the 8 and 9-bit (depending on who made them), 30-pin single in-line memory module (SIMM), which offered a low cost snap in style memory solution that was ideally suited for the 1 and 2 byte processors of that time. While these designs were widely adopted during the late 1980s, their usefulness began to peak during 1989 and 1990 with the adoption of 4-byte processors, which required four 30-pin SIMMs to accomplish a single upgrade increment.

As the computer industry began to invest heavily in design and development strategies, shortly thereafter the 72-pin SIMM emerged, which offered 32 to 40 bits of data (4 bytes) and a board area only 20% larger than a single 30-pin SIMM. Memory makers were striving to develop better performance, and they took what they had learned from the early 30- and 72-pin SIMM's and began to develop more robust memory solutions that could increase performance while being both reliable and cost effective. Obviously to save room here, we have skipped some steps in the evolutionary cycle, but it was from these humble beginnings that the current line of memory solutions arose. The next large step in the cycle was the 168 pin memory dual in-line memory module (DIMM), which were well suited for the high performance Pentium type processors being released by Intel.

The following will assist you with both a visual of the memory type, along with a description, and we have included both current memory types as well as some of the older ones that are still used in some of the older computer system yet today.

Memory Module Types

30 Pin SIMM

The 30 Pin SIMM was the first generation of the SIMM memory family.

They are typically found in older Intel 286 and 386 desktop computer systems. They come in both 8 bit and 9 bit (parity) configurations, with memory ranges of 256K to 8 megabyte, 60ns to 80ns and are  5 Volts only. The DRAM types supported are mostly Page Mode and Nibble Mode DRAM which comes in both DIP, PLCC and SOJ packages.

72 Pin SIMM

The 72 Pin SIMM was the second generation of the SIMM family.

They are typically found in the Intel 486, 486DX, 586 and some early Pentium desktop computer systems. They come in both 32 bit and 36 bit (parity) configurations, with memory ranges of 4, 8, 16 and 32 megabytes. These were normally produced in two voltage, 5V and 3.3V, and theirs speeds ranged from 60ns to 70ns.

Both Fast Page Mode (FPM) and Extended Data Out (EDO) were standard DRAM types offered in 72 pin configurations. Dram chip packaging consisted of DIP, PLCC and SOJ packages.

168 Pin DIMM

The 168 PIN DIMM is what is found in most desktop computers today.

Early on there were three memory types offered in the 168 Pin DIMM form factor, FPM, EDO and Synchronous DRAM (SDRAM). Their configurations include 64bit, 72bit and 80Bit, ECC and Non-ECC, and memory sizes included 16, 32, 64, 128, 256, 512 and 1,024 megabytes. Available voltages included 3.3v and 5v for FPM and EDO, and 3.3v for  SDRAM.

Features added to later versions of the168 Pin DIMM family were the inclusion of a serial EEPROM called the "Serial Presence Detect" which contains information about the module type. Some of the later versions of the SDRAM modules (usually higher cost modules) could reach a maximum frequency of 150Mhz. Present day SDRAM technology has passed this 150 MHz range. Later generations of the 168 Pin DIMM became available as Registered DIMM's or Buffered DIMM's for high-end workstations and servers and Un-buffered DIMM's for most personal computers. There are many variants to be found with 168 Pin DIMM's, as they are the current popular form factor. The post popular of these today are the PC 100 and PC 133 varieties. 


72 Pin SODIMM's are typically found in Pentium II Laptop computer. They come in 64 bit configurations, with memory ranges of 8, 16 and 32 megabyte. These modules are designed around lower power consumption and only one voltage is offered, FPM and EDO at 3.3v. FPM and EDO are the standard DRAM types offered and the packaging is referred to as SOJ.

144 Pin SODIMM

144 Pin SODIMM's are typically used in PC 66 and PC 100 SDRAM Laptop compatible computers. It comes in both 64 bit and 72bit ECC versions and the memory ranges were 16 to 256 megabyte. The SDRAM chips used in 144 Pin SODIMM's are typically SDRAM in the form of TSOP packaging and available in 3.3v only.

100 Pin DIMM

100 Pin DIMMs are primarily used in printers. It comes in both 64 bit and 72bit ECC configurations, and is available in memory ranges of 16 to 128 megabytes. The SDRAM chips used on the 100 Pin DIMM are typically SDRAM in TSOP packaging. Both FPM and EDO were/are used in 100 Pin DIMM.

184 Pin RIMM

The 184 pin RIMM is used on motherboards using the latest Intel i820/i840 chipsets and is referred to as Rambus. The 184 pin RIMM module comes in both 16bit and 18bit ECC configurations, operating frequencies of 600MHz, 700MHz and 800 MHz and are available with memory ranges of 64 through 512 megabytes. The Rambus packaging is referred to as the Ball Grid Array (BGA) form factor. The Rambus modules only require 2.5 volts. There is a 1 GHz Rambus chip under development that was slated for release in 2001.

184 Pin DIMM

DDR SDRAM is the newest of the memory types under development that will be available in the 184 Pin DIMM form factor. The principle difference between conventional SDRAM and DDR SDRAM is its ability to read/write data on both edges of a clock, therefore resulting in faster data transfer. DDR SDRAM will be available in two frequencies, 200Mhz and 266Mhz, and operational voltage is 2.5v. There is speculation (these have not been released to manufacturing as of this writing) that these modules will be available in both 64 bit and 72bit ECC configurations, with memory ranges of 64 megabytes through to 1 gigabyte. The DDR SDRAM chips used are of the TSOP package.

200 Pin SODIMM

The 200 Pin SODIMM module comes in both 64 bit and 72bit ECC configurations, with memory ranges of 64 megabyte through 512 megabyte. DDR SODIMM modules are slated for use in next-generation DDR Laptop applications. The DDR SDRAM chips used on the 200 DIMM are typically in TSOP packaging.


We have devoted a great deal of time on our Web site discussing such memory issues as evolution, types, characteristics and where memory technology appears to be going, but there is another issue that is becoming an increasing problem, and that is Internet Fraud. We are seeing more and more users purchasing memory modules at cut throat prices only to learn later that their new PC-100 or PC-133 module isn't really PC-100 or PC-133 qualified at all. All memory has a basic performance standard which must be met in order to be considered qualified. In the case of PC-100, it must operate at 125MHz without errors, and PC-133 must operate at 150MHz without errors. There are other standardizations that must be met, but these are the basics. Do you need to know what you PC-100 memory really is? If so go here. Wondering if your PC-133 memory module is compliant? If so, go here.

If you have found this information useful to you, won't you please let us know? 

Also, if you feel there is something that should be added or corrected, we would like to hear about that too!

This page updated: 11/12/2000

Copyright ©2000 DEW Associates Corporation. All rights reserved.