Types of ROM

                  Types of ROM

         1. Programmable Read Only Memory (PROM)

        •Empty of data when manufactured

        •May be permanently programmed by the user

      2. Erasable Programmable Read Only Memory (EPROM)

 •Can be programmed, erased and reprogrammed

 •The EPROM chip has a small window on top allowing it to be erased by shining ultra-violet light on it

 •After reprogramming the window is covered to prevent new contents being erased

 •Access time is around 45 – 90 nanoseconds

 mil��
il
���i-font-family:Arial; mso-fareast-font-family:+mn-ea;mso-bidi-font-family:+mn-  cs;color:black; mso-color-index:1;mso-font-kerning:12.0pt;language:en-GB;font-weight:bold'>

üThe contents of ROM are fixed at the time of manufacture

üStores a program called the bootstrap loader that helps start up the computer

üAccess time of between 10 and 50 nanoseconds

3. Electrically Erasable Programmable Read Only Memory (EEPROM)

•Reprogrammed electrically without using ultraviolet light

•Must be removed from the computer and placed in a special machine to do this

•Access times between 45 and 200 nanoseconds

t;
�
ug
���Access time is around 45 – 90 nanoseconds

4. Flash ROM

•Similar to EEPROM

•However, can be reprogrammed while still in the computer

•Easier to upgrade programs stored in Flash ROM

•Used to store programs in devices e.g. modems

•Access time is around 45 – 90 nanoseconds

'f��
sz
���>üThe contents of ROM are fixed at the time of manufacture

üStores a program called the bootstrap loader that helps start up the computer

üAccess time of between 10 and 50 nanoseconds

5. ROM cartridges

•Commonly used in games machines

•Prevents software from being easily copied