ROM and Cache

ROM and Cache

1. Read only memory

   • Internal Memory
     • Data and instructions being stored by the manufacturer at the time of being created
     • Stores data and instructions permanently
     • When the power is turned off
       • The instructions stored in ROM are not lost.
   • Non-volatile memory
     • store frequently used instructions and data
       • To control the basic input and output operations of a computer
     • When the computer is switched on
       • When the computer is switched on
         • A bootstrap loader which is a program in ROM is automatically activated
           • The program loads the operating system into main memory
   • PROM
     • Programmable Read Only Memory
       • Initially blank
       • The manufacturer can write data/program
         • By using special devices
       • Once program or data is written in PROM chip, it cant be changed
       • Error in writing instructions or data
         • The error cant be erased and the PROM chip become unusable
   • EEPROM
     • Erasable Programmable Read Only memory
       • Initially blank
       • User or manufacturer can write program or data
         • By using special devices
       • Data written on EEPROM chip can be errased
         • By using special devices and ultraviolet light
         • Program or data can be changed and new data can be added
       • When is in use
         • The contents can only be read
     • Electrically Erasable Programmable Read only memory
       • Can be written or changed
         • With the help of electrical devices
           • Data stored in EEPROM can be easilly modified

2. Cache

   • SRAM memory
     • Built into the CPU
     • Next to a CPU on a separate chip
   • The CPU uses cache memory
     • to store instructions that are repeatedly needed to run programs
     • Improving overall system speed
   • Main Advantages
     • Cache is physically closer to CPU than main memory
     • Uses SRAM
       • Faster to access than the slower DRAM used by main memory
     • Data transfer within CPU is faster than on the slower data bus
   • Level 1 Cache
     • Found inside the CPU itself
     • Level 1 cache is faster than access to level 2 cache
   • Level 2 Cache
     • Can be found within the CPU housing
     • not within the CPU itself