CISSP certification: ROM and RAM.

  • Memory: Is just 0’s (off) and 1’s (on); switches representing bits.
    • Cache Memory: Closest to the CPU, Fastest, L1 Cache is on the CPU, L2 Cache is connected to CPU but outside it.
      • ROM (Read Only Memory) is nonvolatile (retains memory after power loss); most common use is the BIOS.
        • PROM (Programmable Read Only Memory):
          • Can only be written once, normally at the factory.
        • EPROM (Erasable Programmable Read Only Memory):
          • Can be erased (flashed) and written many times, by shining an ultraviolet light (flash) on a small window on the chip (normally covered by foil).
        • EEPROM (Electrically Erasable Programmable Read Only Memory):
          • These are Electrically Erasable, you can use a flashing program. This is still called Read Only.
          • The ability to write to the BIOS makes it vulnerable to attackers.
        • PLD (Programmable Logic Devices) are programmable after they leave the factory (EPROM, EEPROM and Flash Memory). Not PROM.
          • RAM (Random Access Memory) is volatile memory.
            • It loses the memory content after a power loss(or within a few minutes).
            • This can be memory sticks or embedded memory.
            • SRAM and DRAM:
              • SRAM (Static RAM): Fast and Expensive.
                • Uses latches to store bits (Flip-Flops).
                • Does not need refreshing to keep data, keeps data until power is lost.
                • This can be embedded on the CPU.
              • DRAM (Dynamic RAM) Slower and Cheaper.
                • Uses small capacitors. Must be refreshed to keep data integrity (100-1000ms).
                • This can be embedded on graphics cards.
              • SDRAM: (Synchronous DRAM):
                • What we normally put in the motherboard slots for the memory sticks.
                • Most common now is DDR (Double Data Rate) 1, 2, 3, 4 SDRAM.

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CISSP, C|EH, PMP, CCNP, CompTIA Security+, SCP, CCNA-Security, CCNA, et. Al.

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