There are two standard speeds for SDRAM products: PC-100 and PC-133.

PC-100 modules operate at a 100Mhz clock frequency and achieve a peak bandwidth of 800MB/s.

PC-133 modules operate at a 133 Mhz clock frequency and achieve a peak bandwidth of 1066MB/s.

SDRAM chips use a clock which is synchronized with the CPU's clock. The SDRAM chip is divided into two cell blocks and data is interleaved between the two so that while a bit in one block is being accede, the bit in the other is being prepared for access. This allows the SDRAM to burst the second and subsequent characters at a rate of 10 nsec. (PC-100) or 7.5 nsec. (PC-133).

SDRAM is an older interface technology that has been superseded by DDR, DDR2, or DDR3 in many applications. It may still be the right choice for designs using older microprocessors or chipsets that were designed several years ago. It may also be the right choice for use as an upgrade for systems that have already been installed in the field. You should refer to your system or microprocessor documentation to see if it does use the SDRAM interface. SDRAM modules will not work in DDR or DDR2 sockets or vice-versa so it is important to use exactly the type of module that was originally intended for your application.