MEMORY DEVICES

RAM

Its a temprarely storage devices as it is volatile by nature. Volatile memory are those in which the contents are lost when power is turn off.

  • It is used to hole program (instructions & data) when a processor is active. The larger the Ram greater numbers of instruction it can hold resulting and a faster operations.
  • The access time is same for any address  in memory (that is the physical location of memory word has no effect on how long it take to read from or write in to that location).

TYPES OF RAM

  1. Static RAM (SRAM)
  2. Dynamic RAM (DRAM)

STATIC RAM

  • In static RAM binary values are store using tradchinel flipflop (A logical storage element made up of logic gates that can store a sigle binary bit).
  • It can hold data as long as power is supplied to it. this means that do not required any Refreshing so they are fast.
  • They are more expensive then DRAMs.

EXAMPLE

Cache memory

DYNAMIC RAM

  • These memories are made with cells that store data as charge on capacitors. The presences or abbsences of charge on a capacitor is interpreted as binary 0 to 1.
  • Because capacitor has natural capacity to discharge, DRAM required periodic charge Refreshing to maintan has they are store.

EXAMPLE

Traditional RAM used in PCs.

ROM

It is stand for Read Only Memory. It stores programs and data that are resident to yhe system and are not removed when power is turn off. This type of memory called non-volitile memory.

TYPES OF ROM

  1. PROM
  2. EPRom
  3. EEPROM
  4. Flash Memory

PROM: PROGRAMABLE ROM

  • Once programms is written, remain there forever.
  • Manufacture as blank.
  • Programmer/burner is used to write program.

EPROM: ERASABLE PROM

  • EPROMs are erased when exposed to uv light.
  • Erasure time is 20 min or mor.
  • Smallar is size as compared to EPROM.
  • Their enclurance is 100 programming cycles. (i.e. can be programmed 100 times before the chip gets damaged).
  • Portions of EPROM can not be crased, it is erased completely a time.

EEPROM

  • EEPROMs are erased when subjected to certain electrical voltages.
  • Erasure time is 10ms.
  • Endurance = 100,000 is posible in these chip.

FLASH MEMORY

  • Like EEPROM, it uses electrical erasing technology.
  • Can be erased in 1 or a few seconds.
  • Much faster than EPROM.
  • It is possible to erase just block of memory. Rather than entine chip, does not provide byte-level exposure.
  • Enclerance = 10,000 programming cycle.

 

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