Main Memory: What RAM and ROM Do

Topic: Y2 Functions of the main memory

What main memory is and how it works, explained step by step: RAM and ROM, volatility, memory addresses and how memory stores bits; the features of RAM (capacity, speed and volatility) and the types DDR4, DDR5 and SDRAM.

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What's inside

When you study, the notebook open on your desk is where you work right now: quick to write in and read from, but you clear it when you're done. Your full set of textbooks stays on the shelf. A computer has the same arrangement. Main memory is the desk where the computer works on the programs and data it is using right now. This note explains what main memory does and what makes one kind better than another.

SUMMARIZED NOTES

Year 1: How memory stores bits, RAM and ROM, volatility, memory addresses, and how RAM differs from secondary storage.
Year 2: The features of RAM (capacity, speed and volatility) and the types of RAM (DDR4, DDR5 and SDRAM).

Year 1: RAM, ROM and how memory works

Main memory, also called primary memory, is made up of memory chips connected to the CPU. There are two kinds: RAM and ROM.

RAM: the working memory

When you open an app, it is copied from storage into RAM (Random Access Memory), because the CPU can reach RAM far faster than the hard drive. RAM is the main place for the data and instructions the CPU is working on, and the CPU can access it directly. Each storage location in RAM has a binary number called a memory address, so the CPU can find exactly what it needs.

RAM is volatile: it needs electricity to keep its contents. Switch off the computer, or lose power suddenly, and everything in RAM is lost. That is why you lose unsaved work in a power cut. The amount of RAM affects how many programs can run at once and how much data can be handled smoothly; it is measured in gigabytes (GB).

ROM: the permanent instructions

ROM (Read-Only Memory) is also primary memory, but it is non-volatile: it keeps its data without power. It is generally only read, not changed by normal programs, so it is used for instructions the computer needs every time, such as those used when starting up.

How memory holds bits

Memory stores data as bits. A basic circuit called a flip-flop stores one bit (0 or 1); some RAM, such as SRAM, is built from flip-flops. Eight bits make a byte, and capacities are counted in KB, MB and GB.

RAM vs secondary storage

	RAM (main memory)	Secondary storage (HDD, SSD)
Purpose	Holds what is being used right now	Keeps files and programs permanently
Speed	Much faster	Slower
Capacity	Smaller	Much larger
When power is off	Contents are lost (volatile)	Contents are kept (non-volatile)

Year 2: Features and types of RAM

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