Computer Science : S3 : L6 : ROM and RAM

Storage devices fall into three different categories: 

  • Primary

  • Secondary

  • Tertiary


ROM holds startup instructions for the computer known as the bootstrap. The firmware for the BIOS, (Basic Input and Output System) is included. The computer system uses this after it is powered on to manage the data flow between the computer's operating system and any attached devices, such as the hard disk, video adapter, keyboard, mouse and printer.. It is known as non-volatile meaning it will not lose its data when the power is switched off. ROM is read only memory.


The RAM inside a computer holds all of the data and instructions that are currently being processed by the CPU. In order for any program to be executed, it must first be loaded into the RAM from Secondary storage. This is because RAM has quicker read and write speeds than secondary storage devices. 

The processor will fetch instructions from the RAM directly before decoding and executing them. Within RAM, the memory is split up into separate locations, each of which is given a unique memory address. The processor will use these addresses to access the data stored in RAM. 

Any of the locations in RAM can be accessed in the same amount of time. This is why it is called random access as any location can be accessed at random with no impact on speed. It is volatile meaning contents are lost when the computer is powered off. RAM is read and write.

ROM

  • Read Only Memory

  • Non-volatile / permanent memory

  • Stores the startup instructions when the computer is first switched on (BIOS)

  • It can be read but not changed

RAM 

  • Random Access Memory

  • Volatile / temporary memory

  • Stores data, files that are currently in use

  • It can be written to or read from

  • The contents of the memory can be changed

  • It is quicker to access than secondary storage

  • It has the largest capacity of all main memory