SIMM and DIMM

DIMM stands for Dual In line Memory Module in opposition to SIMM, which simply is Single In line Memory Module. DIMM or SIMM only specifies the package RAM comes in, not the type! . The benefit of a DIMM is that it has a 64 bit (72 bit with parity) wide data path and therefore can be used single in Pentium boards, which normally require two SIMMs.   You can get any type of RAM type for each module, for most PC uses, DIMMs are at present used for SDRAM

Different types of memory

• The Fast Page Mode RAM (FPM RAM)
  The Fast PageMode means, that the RAM logic 'hopes', that the next access will be in the same row, saving time if this should be the case. The fastest access speed of FPM RAM in CPU cycles is 5-3-3-3 for a four data (Byte/Word/Dword) burst read.
  
  Fast Page Mode
  A series of FPM read access's starts with the activation of a row in the DRAM array by providing a row address and bringing RAS LOW. Then, multiple column access's may be executed by cycling CAS. Each CAS cycle includes applying a column address, bringing CAS LOW, waiting for valid data-out, latching data in the system and bringing CAS HIGH to prepare for the next cycle, in that order.
  
• The Extended Data Output RAM (EDO RAM)
  A set of gates latches the output value till read by the CPU, which is important for fast CPUs like Pentiums, it handles better quick sequential reads than FPM RAM. It is a variation of the regular FPM RAM with minor change in the CAS# and data output timing. Data comes out of EDO DRAM more frequently than from standard DRAM. The CAS# timing can be condensed to crank more data out in a given period of time. In the Triton chip set, the difference is X-2-2-2 vs. X-3-3-3 in terms of CPU clocks.
  
  The problem with EDO RAM when looking in the future is that it hardly works with any bus speed higher than 66 MHz, which is already reached. As CPUs demand higher bus speeds, the future of the EDO RAM seems already limited.
  The fastest access speed of EDO RAM in CPU cycles is 5-2-2-2 for a four data (Byte/Word/Dword) burst read.
  
  
• The Synchronous Dynamic RAM (SDRAM)
  SDRAM has gained popularity since it became supported by the Intel Triton VX chipset and all following chipsets, as well as Pentium Pro. As the name states, this RAM is able to handle all input and output signals synchronized to the system clock, which is quite amazing, for that is something a short while ago only Static Cache RAM was able to achieve.
  The fastest access speed of SDRAM in CPU cycles is 5-1-1-1 for a four data (Byte/Word/Dword) burst read, which makes it faster than other standard RAM, however SDRAM handles bus speeds up to 100 MHz ! This will make SDRAM the only viable solution for CPU speeds above 333 which run a 100mhz bus.