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The initial type of the board and connectors were proprietary. This means that the components designed by a particular company will suit only the systems specified by those companies. Or in other words the components designed during the early days were system specific.
Next to the system specific component, the manufacturers manufactured the single inline memory module called the SIMM. The size of the SIMM was usually 3.5 x 7.5 inches. The SIMM memory board used a 30 pin connector. It was a practice to use two such SIMM memory boards both having equal capacity and speed in combination. This is because the width of each bus was more than that of a single SIMM. For example if there is a requirement for a 16 Mb of total RAM then it was been in practice to use two SIMM’s of capacity 8 Mb each. In this way the one can enable the system bus to handle 16 bits of data at a data with each SIMM capable of sending 8 bits of data. As the years passed and with the advancement in the technology, SIMM boards of larger size of 4.25 x 1 inch were manufactured. These memory boards used a 72 pin connector to provide a higher bandwidth and allowed for up to 256 Mb of RAM.
As there was a considerable growth in the processors both in speed and bandwidth capability, the industry started to adopted new technology and standards to cope with that advancement. A new standard called dual inline memory module or DIMM was introduced into the market. The DIMM was more highly capable than the SIMM memory boards. The DIMM had a 168 pin or 184 pin connector and a size of 5.4 x 1 inch. Due to the increase in size, the DIMM was preferred for most of the mother boards as it eliminated the use in pairs. Also DIMM had capacity of handling 8 Mb to 1 GB of data per module.
With the continuous advancement in the system architecture there was another standard proposed by Rambus. This was called the Rambus inline memory module or the RIMM. The architecture is similar to that of the DIMM. The major difference that was detected was in the usage of a high speed special memory bus called the Rambus channel. This certainly increased the speed and bandwidth.
It was during this time that notebook computers became plentiful in the market. Many brands of notebook computers were using proprietary memory modules. The need arose for a newer technology, and this was called the small outline dual inline memory module or the SODIMM. Several manufacturers used RAM based on this SODIMM configuration.
SODIMM cards are small, about 2 x 1 inch (5 x 2.5 cm), and have 144 or 200 pins. The capacity of these types of memory cards varied from the range of 16 MB to 1 GB. These kinds of cards were used in Apple iMac desktop computer instead of traditional DIMMs to reduce the space.
For more info please refer part II of this article.