Page 20 - Computer Science Class 11 Without Functions
P. 20

Give a one-word answer for the following:
                 1.  The high-speed temporary storage in the CPU.
                 2.  The type of operations in ALU that return True or False.
                 3.  An eight-bit sequence.

                 4.  A non-volatile memory that stores instructions for booting.
                 5.  A type of memory that stores frequently used instructions.


        C. Secondary Memory

        In contrast to RAM, the secondary memory stores data and instructions in the computer system permanently. Even
        though ROM also stores data permanently, it is very expensive and does not allow data modification. The secondary
        memory is used to store data and instructions for the long term as it is non-volatile. Further, the secondary memory has
        a much larger storage capacity than the primary memory. It is slower but cheaper than primary memory. However, the
        CPU cannot access secondary memory directly. The contents stored on secondary memory must first be loaded into
        the main memory for processing by the CPU. Secondary memory includes hard disks, compact disks (CDs), memory
        cards, pen drives, and solid-state drives (SSDs). Further, apart from the aforementioned secondary storage media that
        is owned by a computer service centre or a user of a computer system, nowadays, data is also stored in a virtual space
        or cloud, which is managed by service providers like Google, Microsoft, and Amazon. Google Drive is an example of
        virtual storage.
        1.4.3 Data Transfer Between Memory and CPU

        Data is transferred between different components of a computer system (CPU to primary memory and vice versa or
        primary memory to secondary memory, or cache memory to CPU and vice versa) using physical connections called
        buses. There are three types of buses:
           Data Bus: It is used to transfer data between different components.
           Address Bus: It is used to transfer addresses of memory locations for the CPU to perform read/write operations in
           the memory.
           Control Bus: It is used to transfer control signals between various computer components.


                                                                          Input and
                                       CPU             Memory              Output







                                                     Control bus
                                                                                         System bus

                                                     Address bus


                                                       Data bus



                                                     Fig 1.7: System Bus
        The data bus, address bus, and control bus together constitute the system bus. Fig 1.7 depicts the flow within the
        system bus. Data entered from an input device is stored in the main memory. The CPU then accesses this data using a
        data bus. The address of the memory location from where data will be accessed is communicated via the address bus.

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