Nowadays, we have various speeds of memories, for example 133MHz, 266MHz, 333MHz. Let's take a look on the overview of the evolution of memory.
| Year Introduction | Technology | Speed Limit |
| 1987 | FPM (Fast Page Mode) | 50ns |
| 1995 | EDO (Extended Data Out) | 50ns |
| 1997 | PC66 SDRAM | 66MHz |
| 1998 | PC100 SDRAM | 100MHz |
| 1999 | RDRAM | 800MHz |
| 1999/2000 | PC133 SDRAM | 133MHz |
| 2000 | DDR SDRAM -I | 266MHz |
| 2001 | DDR SDRAM -I | 333MHz/400MHz |
| 2003 | DDR SDRAM -II | 400MHz? or 533MHz? |
FPM: Fast page mode. A specialized method of DRAM operation that improves DRAM performance over page mode operation under certain operation conditions. FPM enabled faster access to data located within the same row.
EDO: Extended data output. A variation of fast page mode and is faster than conventional DRAM. It can begin retrieving the next block of memory at the same time that it sends the previous block to the CPU. Conventional DRAM can only handle one block of data at a time.
SDRAM: Synchronous dynamic random access memory. Operates at a faster rate than both FPM and EDO DRAM. It has a clock input that synchronizes all operations.
RDRAM: Rambus dynamic random access memory. A high-speed memory interface that improves the performance of conventional DRAM, but requires a larger die size and more manufacturing steps.
DDR SDRAM: Double-data-rate synchronous DRAM. A type of SDRAM that transfers data on both the rising and falling edge of the clock signal, which effectively doubles the memory chip's data throughput.
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