Virtual Memory

1.2.3

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Running out of Memory

There are many approaches that we might take when we are running low on memory:

Installing more Random-Access Memory

When we run out of RAM, we can purchase and install more RAM so that we can store more data.
This is not always ideal because:
- RAM can be expensive.
- We may only need more memory on a temporary basis.

Virtual Memory is a technique where we use secondary storage as if it were RAM.
Virtual memory is not always ideal since:
- Virtual Memory can have negative impacts on performance.
- Virtual Memory can have negative impacts on the health of Solid State Disks (SSDs).
- We might have limited space in secondary storage.

Terminating processes

Each program/process will use a certain amount of memory.
By closing some processes that we are not using, we can free the memory that they are using.
This is not always possible because we may need all the processes.

How Virtual Memory Works

Virtual Memory allows us to access more memory than we have by setting aside some secondary storage space to act as extra memory.

Paging

Memory can be split into sections called 'pages'.
Virtual Memory works by moving these pages between the Random Access Memory (RAM) and the secondary storage.

Move pages to Hard Disk Drive (HDD)

If a page is not being used, then we might want to put it into Virtual Memory.
When a page is moved to the HDD and not being used, it is put into a special file called the pagefile.
Other processes can then use the memory that we just freed in the RAM.

Move pages to RAM

When we want to use a page again, we first need to move it back to the RAM.
We do this by swapping the page that we want with one that is already in the RAM.

1Computer Systems

1.1Systems Architecture

1.1.1Architecture Introduction

1.1.2Von Neumann Architecture

1.1.3Fetch-Execute Cycle

1.1.4Factors Affecting CPU Performance

1.1.5Elements of Computer Systems

1.1.6Exam-Style Questions - Von Neumann Architecture

1.2Memory & Storage

1.2.1Types of Memory

1.2.2Flash Memory

1.2.3Virtual Memory

1.2.4Exam-Style Questions - Primary Memory

1.2.5Capacity

1.2.6Solid State Storage

1.2.7Magnetic Storage

1.2.8Examples of Magnetic Storage

1.2.9Optical Storage & its Properties

1.2.10Examples of Optical Storage

1.2.11End of Topic Test - Computer Systems

1.2.12Grade 9 - Storage

1.2.13Exam-Style Questions - Storage

1.2.14Units of Information

1.2.15Number Bases

1.2.16Converting Number Bases

1.2.17Hexadecimal

1.2.18Binary Arithmetic

1.2.19Representing Text

1.2.20ASCII & Unicode

1.2.21Representing Images

1.2.22Representing Sound

1.2.23Data Compression

1.2.24End of Topic Test - Representation

1.2.25Exam-Style Questions -Data Conversions

1.3Computer Networks, Connections & Protocols

1.3.1Benefit of Networks

1.3.2Network Performance

1.3.3Networks: How Do Packets Get Routed?

1.3.4Types of Networks

1.3.5Client-Server Model

1.3.6Pros & Cons of Client-Server Model

1.3.7Peer-to-Peer Model

1.3.8Pros & Cons of Peer-to-Peer Model

1.3.9Network Hardware

1.3.10What is the Internet?

1.3.11URLs

1.3.12DNS & Web Hosting

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Flash Memory

Exam-Style Questions - Primary Memory