MEMORY HIERARCHY Memory Primary Secondary Cache RAM ROM Hard Disk, Magnetic Tape, Static PROM CD, DVD, Zip Disk etc Dynamic EPROM EEPROM
PRIMARY MEMORY Provides storage for data and instructions on which control unit and arithmetic logic unit can operate. Data or instructions entered through input device is stored in it. Holds the program and data currently being used for computer and also stores intermediate results. Operates at the highest speed and can be access directly by central processing unit(CPU).
TYPES OF PRIMARY MEMORY Random access memory(RAM) Read/write memory Place in a computer where operating system, application programs, and data in current use are kept for quick access Data stays only as long as the computer is running 2 types Static RAM(SRAM) Dynamic RAM(DRAM)
TYPES OF PRIMARY MEMORY (CONT.) Static RAM(SRAM) Stands for Static Random Access Memory Retains the data as long as power is provided to the memory chips Doesn’t need to be ‘refreshed’ periodically. Very fast and expensive as compared to DRAM. Used in specialized applications in computer.
TYPES OF PRIMARY MEMORY (CONT.) Dynamic RAM(DRAM) Stands for Dynamic Random Access Memory Must be continually ‘refreshed’ in order for it to maintain the data Cheaper and smaller than SRAM Used as system memory in most of the computers
TYPES OF PRIMARY MEMORY (CONT.) Read Only Memory(ROM) Permanent memory Contents are not lost when the power supplies are switched off. User can’t write in it Stores permanent programs and other types of information needed by computer to execute users programs
TYPES OF PRIMARY MEMORY (CONT.) Types of ROM Programmable Read Only Memory(PROM) Program stored in PROM can be modified once by the user. Once chip has been programmed, recorded information cannot be changed Erasable Programmable Read Only Memory (EPROM) Can be erased and reprogrammed Needs to be removed from the proccessor and exposed to ultraviolet light for sometime before it can accept any new contents.
TYPES OF PRIMARY MEMORY (CONT.) Electrically Erasable Programmable Read Only Memory(EEPROM) User-modifiable read-only memory (ROM) that can be erased and reprogrammed (written to) repeatedly through the application of higher than normal electrical voltage generated Limited to single byte operations which made them slower Retains it’s contents even when the power is turned off.