ANSWERS: 1
  • Memory modules are an important part of a computer. Without memory, there would be no way to load programs to run. Over the years, as needs have changed, so have memory types.

    Pin Count and Spacing

    In order to be a true memory module, said module must have the appropriate number of contacts and spaces between said contacts for the type of memory required. The earliest memory modules were 30 pins. The next generation used 72, with a space dead center between pin 36 and 37. SDRAM had 168 pins, and two notches.

    Package

    Before memory modules, the way you added RAM to a computer was via individual RAM ICs. This was painstaking and prone to damage to the chips via bent and broken pins. Memory modules removed this danger by packaging all of the RAM ICs on a small PCB with contacts that made it easy to install.

    Bus Architecture

    Each type of memory module must meet specific criteria for speed and latency ratings for its type to be a real memory module. For example, for a memory module to be labeled as a PC133 CL2 SDRAM, it must be able to run on a 133MHz system bus at CAS Level 2, it must be 168 pins, with two notches at the appropriate points and operate on 3.3 volts.

    Capacity

    All memory modules must follow industry standards in regard to capacity. A memory module cannot be of capacity other than the designated capacities. In general, these capacities are powers of two, and in today's machines, are very large. For example, you cannot have a 384MB memory module. You can have a 128MB module, and a 256MB module, but no odd amounts are accepted.

    Dimensions

    A memory module cannot be any longer than the slot that it is designed for use in, and cannot be any taller than the specifications call for. In general there is no minimum height, but you will never see a 5-inch-tall DDR memory module.

    Source:

    "High Performance Memories: New Architecture DRAMs and SRAMs --Evolution and Function;" Betty Prince;1999

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