DDR SDRAM

DDR SDRAM

Double data rate (DDR) SDRAM memory is an evolutionary design of standard SDRAM in which data is transferred twice as quickly. Instead of doubling the actual clock rate, DDR memory achieves the doubling in performance by transferring twice per transfer cycle: once at the leading (falling) edge and once at the trailing (rising) edge of the cycle. DDR SDRAM uses a new DIMM module design with 184 pins. DDR DIMMs are rated for either PC1600 (200MHz x 8) or PC2100 (266MHz x 8) operation or normally run on 2.5 volts. They are basically an extension of the PC100 and PC133 DIMMs redesigned to support double clocking, where data is sent on each clock transition (twice per cycle) rather than once per cycle as with standard SDRAM.

A typical DDR SD RAM

Primary Storage or Main Memory (RAM)

Primary Storage or Main Memory (RAM) :-

Primary storage, presently known as main memory or simply RAM (Random Access Memory), is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them as required. Any data actively operated on is also stored there in uniform manner.

Memory stores three basic categories of data.

1. Operating system and other system software that control or maintain the computer and its devices
2. Application programs that carry out a specific task such as word processing etc.
3. Data to be processed by the application programs and resulting information.

 RAM varies in size like 128 MB, 256 MB, 512 MB to 4 GB.  RAM can not store data and instruction permanently. When we switch off the computer, all data and instructions from RAM are washed or vanished. Therefore it is called volatile memory.