SIMMs (Single Inline Memory Modules) are the most common memory module format in use today for PCs, because of the thousands of older computers which use them. EDGE Memory™ maintains one of the most comprehensive inventories of these modules in the world, including the older, smaller and harder to locate upgrades. Older SIMMs are created using circuit boards with 30 pins, while newer ones have 72 pins (computer motherboards support one or the other, but not both). They are generally available in sizes from 1 megabyte (MB) to 64MB, and can be 'single sided' (with DRAM chips on one side of the board only) or 'double sided' (chips on both sides).