Understanding SDRAM Latency

Do you ever wonder what the numbers 2.5-3-3-5 mean when you purchase RAM? Well, here is a technical explanation of the meaning of those numbers. For the non-technical people, smaller the number, the better the RAM!

The four numbers are related to tCAS-tRCD-tRP-tRAS.

• tCAS: The number of clock cycles required to read a column of data on the SDRAM stick.
• tRCD: The delay between the Row Address Strobe (RAS) and the CAS. The represents the delay between the CPU defining the row and column of the memory block and the actual read or write to that row and column.
• tRP: Row precharge time. The number of clock cycles needed to terminate access on a given row, and to open access on the next row.
• tRAS: Active to precharge delay. The number of clock cycles between the data request and precharge command of a given row inside a memory block.
  

For a further understanding, check out: http://en.wikipedia.org/wiki/RAM_latency, Enjoy!