Storage Structure : The CPU can load instructions only from memory, so any programs to run must be stored there. General-purpose comoputers run most of their programs from rewritable memory, called main memory (also called random-access memory, or RAM). Main memory commonly is implement in a semiconductor technology call as dynamic random-access memory (DRAM).
Computers use other forms of memory as well, we have already mentioned read-only memory, ROM) and electrically erasable programmable read only memory EEPROM. Because ROM cannot be change, only static programs, such at the bootstrap program describe earlier, are store there. The immutability of ROM is of use in game cartrides. EEPROM can be change but cannot be change frequently and so contains mostly static programs. For example, smartphones have EEPROM to store their factory-installed programs.
All forms of memory provide an array of bytes. Each byte has its own address. Interaction is achieve through a sequence of load or store instructions to specific memory addresses. The load instruction moves a byte or word from main memory to an internal register within the CPU, whereas the store instruction moves the content of a register to main memory. Aside from explicit loads and stores, the CPU automatically loads instuctions from main memory for execution.
More About Storage Structure –
A typical instuction-execution cycle, as executed on a system with a Von Neumann architechture, first fetches an instruction from memory and stores that instruction in the instruction register. The instruction from memory and stores that instruction in the instruction register. The instruction is then decode and may cause operands to be fetch from meory and store in some internal register. After the instruction on the operands has been execute, the result may be store in memory.
Ideally, we want the programs and data to reside in main memory permanently. This arrangement usually is not possible for the following two reasons:
- Main memory is usually too small to store all needed programs and data permanently.
- Main memory is a volatile storage device that loses its contents when power is turn off or otherwise lost.
Thus, most computer systems provide secondary storage as an extension of main memory. The main requirement for secondary storage is that it be able to hold a large quantities of data permanently.
