---
title: What_is_memory
tags: [memory]
created: Friday, July 12, 2024
---

# What is memory ?

## Why do we need memory?

> A CPU is just an operator on memory. It reads its instructions and data from
> the memory and writes back out to the memory. (Ward 2021)

When a [CPU](CPU_architecture.md) executes a program, it needs a place to store
the program's **instructions** and **related data**. This is the role of memory.

## What is memory?

The data that comprises a program is a series of bits. The basic unit of memory
storage is a **memory cell**: a circuit that can store a single bit.

## Memory types

There are two types of memory: [SRAM and DRAM](./DRAM_and_SRAM_memory.md). Both
types of RAM memory are _volatile_ : the memory is only retained whilst the
computer has a power supply and is wiped when the computer is rebooted. This
contrasts with the memory of the harddisk which is non-volatile and is retained
after a reboot.

Programs that are executing are loaded into memory because the chips that
comprise memory can read and store data much faster than the harddisk. It would
be possible to run a program from the harddisk but it would be 500 - 1000 times
slower than memory.

## Related notes