Internal memory

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Internal memory

  1. 1. Internal Memory
  2. 2. Introduction Computer memory exhibits different types of technique, organization, performance, size and cost. But, no technology is optimal in memory requirements for a computer system. As a result, a computer equipped with a hierarchy of memory subsystems. Some are internal to the system – RAM, ROM, CACHE External memories are Hard disk, Optical and Pen drive etc.,
  3. 3. RAM Storage cell unit consists of N cells each of which can store 1 bit either 0 or 1. Every location of RAM accessed independently. So, the access and cycle times can constant. The address of memory location transferred through MAR using address bus. The address then proceed by the address decoder. Which select required location in storage unit.
  4. 4. RAM The contd., contents of the selected location placed in IR through MDR processor register. The R/W control line specifies the type of access to be performed. Write operation, the word to be place in MDR and the address specified in MAR and then transferred to selected cell. DDR RAM-Double Data Rate synchronous dynamic random access memory
  5. 5. RAM
  6. 6. ROM Data are written into a ROM when it is manufactured. ROM is mask programmed by the manufacturer in the factory with the contents ordered by the customers. The contents are fixed by metal masks used during chip fabrication. Once programmed, the contents cannot be erased. Even a single bit wrongly programmed the ROM chip is useless.
  7. 7. Application Used to store control programs such as micro program. Character generation, code conversion, etc.,
  8. 8. Boot screen
  9. 9. PROM-Programmable ROM PROM is a field programmable device. The customer buy a blank PROM and store desired data using PROM programmer(burner). Programmability achieved by inserting a fuse at point P. Before programmed, the memory contains all 0s. The user can insert 1 by burning out the fuse in the particular cell using high current pulse. The PROM chip can be programmed only once and its contents cannot be erased. PROM are flexible , faster and less expensive because they can be programmed directly by the user.
  10. 10. Application-PROM Boot program in micro computer
  11. 11. PROM
  12. 12. PROM
  13. 13. EPROM-Erase programmable ROM A rewritable chip that holds its contents without power. Previous data can be erased and new data can be inserted EPROM chips are written on an external programming device before being placed on the circuit board. Capable of retaining stored information for a long time.
  14. 14. EPROM Eraser contd., requires breakup the charges trapped in the transistors of memory cell.[this is done by break the chip to ultraviolet light]. This reason EPROM packaged with transparent window. Disadvantages: Entire EPROM is erased as a whole and selective erasing is not possible. Should be removed from the chip for reprogramming.
  15. 15. EPROM
  16. 16. EEPROM-Electrically Erased PROM It can be both programmed and erased electrically( flashed back to Zero). They do not need to removed when the chip content erasure. Also, erase selected content in the chip. Erasing and programming dynamically without removing the EEPROM from the circuit. Disadvantages: Different voltages are required for erasing, reading and writing the data.
  17. 17. Application Used as ROM Critical system setup information in a nonvolatile way.
  18. 18. EEPROM
  19. 19. EEPROM
  20. 20. EEPROM
  21. 21. Flash Memory Recent kind of EEPROM is flash memory. Which is erased by ultraviolet light. EEPROM is byte erasable whereas, flash memory is a block erasable. Like a EEPROM when erasing the contents of flash memory no need to remove from the circuit. In flash it is possible to read the contents of a single cell, but is only possible to write an entire block of cells.
  22. 22. Flash memory It contd., need single power supply and consume less power. Application: Cell phones, hand held devices, digital camera, washing machine, AC, Tablet etc. NOTE: low power consumption of flash memory makes it attractive for use in portable equipment that is battery driven
  23. 23. Flash Card Mount flash chips on a small card. That card simply plugged into a slot. 64 MB can store 1 hour songs. Now a days, the device can equipped with up to 32GB flash memory.
  24. 24. Speed, size and Cost SRAM chip is very fast memory in the computer system. but it is expensive because their basic cells have 6 transistors. Which impossible to packaging a very large number of cells onto a single chip. Cost wise also expensive. Cache memory can be implemented based on SRAM. Alternative is to use DRAM, which can have same basic cells and thus much less expensive. But significantly slower. Still it is small in size compared to magnetic drives.
  25. 25. Speed, size and Cost Main memory can be build with DRAM. Secondary storage- large memory space with reasonable price but much slower than semiconductor memory unit.
  26. 26. conclusion Huge amount of cost-effective storage can be provided by magnetic disk. Main memory can be built with DRAM. SRAM to be used in smaller unit where speed is of the essence.(Cache)
  27. 27. SPEED
  28. 28. SPEED Fastest access is to data held in processor registers. There are often two levels of cache, the primary cache inside processor refer to as L1. secondary cache placed outside referred as LEVEL 2(L2) usually SRAM chip. Next level in the hierarchy is called main memory. The typical main memory is about ten times slower than the access for the L1
  29. 29. SPEED The bottom level in the hierarchy is called the secondary memory such as magnetic disk. Disk provide a huge amount of inexpensive storage. But they very slow.

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