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Physical memory

From Academic Kids

The memory hardware (normally RAM) installed in a computer. The term is only used in contrast to logical memory. It also includes the on-chip cache, L2 cache and processor registers.

This type of memory is slower than on-chip cache but is significantly cheaper. In a trade-off between cost and speed, systems have very little on-chip cache (512 kilobytes) and lots of RAM (256 megabytes). The operating system swaps information between the RAM and the swap file to try and ensure that the memory requested by programs is found in RAM. If this doesn't happen, then the user will have to wait until the memory location is loaded from the swap file into the RAM, hindering performance.

Physical memory has been available in various speed's over time. Historically, DIMM's were used which provided very little storage. These were replaced by DRAM and then SDRAM. SDRAM provided memory access at 66 megahertz, 100 megahertz and finally 133 megahertz. However much like DIMM, it's lifespan was limited. There was a need for even faster technology because as memory size increases, access speed needs to increase in a linear relationship otherwise there is no significant speed advantage to using RAM whatsoever. With the advent of higher front speed bus speeds, higher speed memory was introduced in the form of DDR, and then DDR2 at speeds of 533 megahertz. With the 64 bit revolution, memory speed will once again need to grow to accommodate another speed increase.

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