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INTERNAL MEMORY (Semiconductor Memory (RAM Basics (A capacitor is like a…

- - - - Primary Storage / Main Memory
      - made from semiconductor devices.
      - store program temporarily (before, in between, and after the execution)
      - Operating System Programs
        Application Programs
        Data
        Results
    - - made from magnetic, optical devices
      - store programs and data permanently.
  - - - Exhibit 2 stable (or semistable) states (represent binary 1 and 0).
      - Capable of being written into (at least once), to set the state.
      - Capable of being read to sent the state.
- - - - manufacture the information into the chip
      - better not make a mistake
    - - can be written once (blowing fuses with a high voltage)
    - - shine a UV light on it and it disperses the charge
      - can program it electronically using a high voltage
    - - Can erase a byte or a block using a high voltage
      - Can program electronically
    - - Program electronically, and erase a block of memory in 1-2 seconds using a high voltage
  - - - Select
        
        selects a memory cell for a read or write operation.
      - Control
        
        indicates read or write.
      - Data in
        
        for writing, provides electrical signal that sets the states of the cell to 1 or 0.
      - Sense
        
        for reading, used for output of the cell’s state.
  - - - -Bits stored as charge in capacitors
        -Charges leak
        -Need refreshing even when powered
        -Simpler construction
        -Smaller per bit
        -Less expensive
        -Need refresh circuits
        -Slower
        -Main memory
        -Essentially analogue
        (Level of charge determines value)
    - - Write
        
        Voltage to bit line (High for 1 low for 0)
        
        Then signal address line(Transfers charge to capacitor)
      - Read
        
        Address line selected(transistor turns on)
        
        Charge from capacitor fed via bit line to sense amplifier
        (Compares with reference value to determine 0 or 1)
        
        Capacitor charge must be restored
    - - -sending a charge through the appropriate column (CAS) to activate the transistor at each bit in the column.
        
        When writing, the row lines contain the state the capacitor should take on.
        
        When reading, the sense-amplifier determines the level of charge in the capacitor. If it is more than 50 percent, it reads it as a 1; otherwise it reads it as a 0. The counter tracks the refresh sequence based on which rows have been accessed in what order.
        
        The length of time necessary to do all this is so short that it is expressed in nanoseconds (billionths of a second). A memory chip rating of 70ns means that it takes 70 nanoseconds to completely read and recharge each cell.
    - - Both volatile
        -Power needed to preserve data
        Dynamic cell
        -Simpler to build, smaller
        -More dense
        -Less expensive
        -Needs refresh
        -Larger memory units
        Static
        -Faster
        -Cache
  - - - -uses a completely different technology. A form of flip-flop holds each bit of memory
        -A flip-flop for a memory cell takes four or six transistors along with some wiring, but never has to be refreshed.
        -significantly faster than dynamic RAM. However, because it has more parts, it takes up a lot more space on a chip than a dynamic memory cell. Therefore, you get less memory per chip, and that makes static RAM a lot more expensive.
    - - Bits stored as on/off switches
        No charges to leak
        No refreshing needed when powered
        More complex construction
        Larger per bit
        More expensive
        Does not need refresh circuits
        Faster
        Cache
        Digital (Uses flip-flops)
    - - -Transistor arrangement gives stable logic state
        -State 1
        (C1 high, C2 low
        T1 T4 off, T2 T3 on)
        -State 0
        (C2 high, C1 low
        T2 T3 off, T1 T4 on)
        -Address line transistors T5 T6 is switch
        -Write – apply value to B & compliment to B
        -Read – value is on line B
  - - - Written during manufacture
        -Very expensive for small runs
        Programmable (once)
        -PROM
        -Needs special equipment to program
        Read “mostly”
        -Erasable Programmable (EPROM)
        -Erased by UV
        -Electrically Erasable (EEPROM)
        -Takes much longer to write than read
        -Flash memory
        -Erase whole memory electrically
  - - - Basic DRAM same since first RAM chips
        Enhanced DRAM
        -Contains small SRAM as well
        -SRAM holds last line read
        Cache DRAM
        -Larger SRAM component
        -Use as cache or serial buffer
  - - - Adopted by Intel for Pentium & Itanium
        Main competitor to SDRAM
        Vertical package – all pins on one side
        Data exchange over 28 wires < 12 cm long
        Bus addresses up to 320 RDRAM chips at 1.6Gbps
        Asynchronous block protocol
        (480ns access time
        Then 1.6 Gbps)