Lesson 4. Memory

Lesson Objective

Understand the difference between RAM and ROM.
Explain how memory is managed in a computer system.
Identify appropriate RAM and ROM requirements for different systems.

Lesson Notes

Random Access Memory - RAM

RAM is volatile, meaning that the information stored in it is erased when you restart or shut down your computer.

It temporarily holds the files you are currently working on.

When you switch between programs or pages, the data stored in RAM is instantly available.

Slower than cache, faster than secondary storage.

Read Only Memory - ROM

ROM is non-volatile, which means the information is permanently stored on the chip. Turning off the computer does not impact ROM.

ROM stores instructions that do not change, such as the initial boot-up portion of the software or firmware instructions for devices like printers.

RAM and ROM Requirements

The amount of RAM and ROM a system needs depends on the purpose and type of system.

Non-Embedded Systems	Embedded Systems
Non embedded systems usually have more RAM than ROM because they often need to write to memory.	Embedded systems usually have more ROM than RAM because they don't write much data to memory.
ROM is typically used for the BIOS, which doesn't need a lot of memory.	Don't usually have secondary storage, so ROM is used to store everything.
ROM and RAM is often stored away from CPU.	RAM and ROM are often stored on the same chip as the CPU to reduce physical space.

Memory Management

Cache

Cache is very fast RAM that is close to the CPU. Data that needs to be processed by the CPU is stored in the cache. The larger the cache size, the more data can be stored closer to the CPU.

Virtual Memory

Temporary storage created on the Hard Disk when the RAM is full. Frees up space on the RAM to load new applications.

Memory Hierarchy

The higher you go up the memory hierarchy you go the faster the data transfers become. However the capacity of the memory components gets smaller.

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