About RAM Chips
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There are 3 main types of RAM (Random Access Memory) modules that are used in the PC, namely the so called Operative RAM, the Cache RAM, and the Graphics RAM. Requirements, topics and the internal structures are different for these types.


Operative RAM

  • Normal DRAM - type 1. (Dynamic Random Access Memory) Typical speed is between 70-110 ns.

  • Normal DRAM - type 2. So called "Fast Page Mode DRAM" The typical speed is 60-70 ns. This type of RAM is used in most 286-386-486-5x86 systems. (Not so fast and reliable as EDO DRAM.)

  • EDO DRAM. (Extended Data Out Dynamic RAM). Speed between 70-50 ns. Fast and reliable RAM type. Officially supports clock speeds up to 66 MHz, but it often works also at 75MHz. If higher clock frequency is required, SDRAM must be used. Even if it is declared so, the EDO DRAM can NOT work in 486-5x86 motherboards! Another problem, that it is not easy to distinguish the EDO DRAM from the normal FP DRAM just by looking at the chips. Fortunately, any Pentium compatible motherboard will identify and show the type of the RAM during the booting process!

  • SDRAM (Synchronous Dynamic RAM). The fastest DRAM for operative memory - typically 8-15 ns, however, it's reliability is NOT perfect. It is frequently used, when 75-83 MHz or even higher clock frequency is needed.


    Cache RAM

    For the fastest execution, the Cache RAMs are static types, or in other words they do not need periodic refreshing.

  • SRAM (Static Random Access Memory). Typical speed is between 35-12 ns. In good quality 486-5x86 systems usually 256kB/15ns were used.

  • PBC RAM (Pipelined Burst Cache RAM). In this type of RAM a pipeline is used in order to improve the accessability. Especially in burst mode can be the data transfer high, up to 200 MByte/s or more, like in the case of Intel HX chipset.


    Graphics RAM

    For graphics purposes the same types of memories can be used like in the case of operative RAM. However, the speed is usually faster, to compensate the lack of the cache memory on the graphics card. There are special graphics memory types too.

  • Normal DRAM - type 1. Speed is between 70-110 ns.

  • Normal DRAM - type 2. FP Mode DRAM, with typical speed of 70-45 ns. (45ns FP DRAM was used for example with the ET4000/W32P chip.)

  • VRAM (Vertical RAM). It supports the simultaneous displaying and the communication with the processor, which is very beneficial in the case of high-refresh rate (professional) graphics system. The attainable effective speed is similar to that of the 45ns DRAM equipped systems.

  • WRAM (Windows RAM). It is similar to the VRAM, but even faster.Only in Matrox made graphics cards are used.

  • EDO DRAM. Speed between 60-35 ns.

  • EDO VRAM. Speed between 60-35 ns. Thanks to the VRAM like structure, higher refresh rates can be reached.

  • SDRAM Speed is between 8-15 ns. Very fast.

  • SDRAM Speed is between 8-15 ns. Very fast.

  • MDRAM (Multibank DRAM). Simply the fastest RAM type. It goes over 1 GigaByte/s throughput! Only with ET6000 and ET6100 based graphics cards are used from Tseng Labs. (Unfortunatelly, because of marketing issues, this type of RAM is getting out of the production.)

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