Memory and storage Study Guide

Primary storage, often referred to as main memory, is crucial for a computer's operation because it holds data and instructions that the Central Processing Unit (CPU) needs to access quickly. This type of storage is volatile, meaning its contents are lost when the power is turned off. The two main types of primary storage are Random Access Memory (RAM) and Read-Only Memory (ROM).

RAM is the computer's working memory. When you run programs or open files, they are loaded from secondary storage (like a hard drive or SSD) into RAM. The CPU then fetches instructions and data from RAM to perform tasks. Because RAM is much faster than secondary storage, this allows the CPU to process information rapidly. The more RAM a computer has, the more programs and data it can handle simultaneously without significant slowdowns.

ROM, on the other hand, is non-volatile. It contains essential system instructions, such as the computer's startup sequence (BIOS/UEFI), which are permanently stored and do not disappear when the power is off. This information is critical for the computer to boot up and initialise its hardware. The CPU can only read data from ROM; it cannot write new data to it under normal operation, hence 'read-only'.

The CPU uses various registers for extremely fast temporary storage of data and instructions during processing. These are located directly within the CPU. Cache memory, another type of fast primary storage, sits between the CPU and RAM. It stores frequently accessed data and instructions from RAM, allowing the CPU to retrieve them even faster than from RAM itself. There are often multiple levels of cache (L1, L2, L3), with L1 being the fastest and closest to the CPU.