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Computing Academy GCSE Computer Science

ROM and Virtual Memory

ROM and Virtual Memory Read Only Memory (ROM) Every time you switch on your computer it performs a sequence of tasks such as checking that all of the hardware is present, checking that a keyboard and mouse is connected and checking to ensure that the HDD or SSD contains the operating system; this is known as a boot sequence. We know that RAM is volatile, so once the computer is turned off, everything in RAM is wiped. Part of the boot sequence involves checking the HDD or SSD and we know that these storage systems are too slow, so the instructions necessary to perform the boot sequence can’t be stored here. 33

This is where Read Only Memory (ROM) comes in. ROM is non-volatile so it stores data even when the power is turned off. ROM is also very quick which is important when we’re trying to boot up a computer and don’t want to be kept waiting. Most computers have a ROM chip built into the motherboard which stores this boot sequence. When you turn on a computer the ROM chip gets to work, performs the necessary checks and begins to boot the operating system. Virtual Memory Computers load data and instructions into RAM before passing them to the CPU for processing. RAM is used as HDDs and SSDs are too slow. Sometimes, however, computers do not have enough RAM to cope with all of the jobs we are trying to do. When this happens, RAM needs to dump some of the data it has stored that isn’t currently being used into Virtual Memory in order to free up space in RAM for more urgent jobs. When necessary the operating system designates part of the HDD or SSD as Virtual Memory that can be used by RAM as a temporary extension. HDDs and SSDs are slow in comparison to RAM, so computers using Virtual Memory will suffer from a significant reduction in performance. Users will notice this as they try and switch between windows and applications. 34

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