The packaging is simply the entire makeup of a unit of memory, such as the SIMM or DIMM. Since the memory chips themselves are way too small, they must be combined and put onto a medium that can be worked with and added to a system. So, designers took the memory chips, placed them on a small fiberglass card, and created the memory module.

There are several different package styles which one may see for memory:

• DIP (Dual In-Line Package) - This is the old classic “chip” package of memory modules, the kind with small pins undrneath that are plugged into pin sockets. While this design led to the ability to remove as required, it also led to the issue of broken memory pins. This type of package is only seen on old systems (such as those in the 286 era and before) and old video cards.


• SOJ (Small-Outline “J” lead) - This is a more modern type of package often found on memory SIMMs or sometimes with BIOS chips. It is similar to the DIP package, but is designed for surface mounting by having the leads protrude from the side of the package, but bent down under the package in the shape of a “j”.


• TSOP (Thin, Small-Outline Package) - This is also a surface mounting package, but it requires a very small space, and is thus used on PCMCIA cards, as well as in notebooks and on some video cards.


• BGA (Ball Grid Array) - A newer packaging method in which the chips are attached using small balls of solder underneath the chip. The advantage to the manufacrturer is that they are cheaper to make, allow more capacity, allow better heat dissipation and better electrical performance. There have been various variations of this packaging style: Fine-BGA, Tiny-BGA, etc. , all various advancements off of the BGA standard. This type of package is most common today in heavily-used memory modules, including Rambus.

Finally, engineers put the chips on SIMMs, or Single Inline Memory Modules, or DIMMs, Double Inline Memory Modules. SIMMs use a 32-bit memory bus whereas DIMMs use a 64-bit memory bus. These cards are placed in a socket on the motherboard, like a card in a slot, then latched in. This design eliminated problems of the past, and made upgrading memory a breeze due to providing standardization which other manufacturers could rely on.

SIMMs

SIMMs come in two sizes, 30-pin and 72-pin. The 30 pin SIMMs usually came with small amounts of memory (smaller than 8MB). They are not used now, being mainly used in earlier 486’s and older machines. The 72-pin SIMMs were much more popular, and were used on many motherboards until SDRAM came into the picture. Although you will occasionally see 72-pin SIMMS still in use, it is usually only if you are opening up an old system.

For pinout info: see 30-pin pinout or 72-pin pinout.

SIMMs come in both single sided and double sided designs. This refers to whether the SIMM has memory chips on one side of the SIMM or both. Usually, 1, 4, and 16MB SIMMs are single sided. Other sizes are double sided. Some double sided SIMMs are actually two single sided SIMMS back to back, where they are wired together within the fiberglass module. These designs operate a little different electrically, explaining why some boards only use SIMMs of certain sizes.