What is Memory Partitioning? - Definition & Concept

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  • 0:04 What Is Memory Partitioning?
  • 0:21 Fixed Partitioning
  • 1:45 Variable Partitioning
  • 2:49 Dynamic Partitioning
  • 4:04 Compaction
  • 4:30 Lesson Summary
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Lesson Transcript
Lyna Griffin

Lyna has tutored undergraduate Information Management Systems and Database Development. She has a Bachelor's degree in Electrical Engineering and a Masters degree in Information Technology.

Expert Contributor
Maria Airth

Maria has a Doctorate of Education and over 20 years of experience teaching psychology and math related courses at the university level.

In this lesson we will understand the definition and concept of memory partitioning. We will examine the different type of memory partitions. We will highlight the pros and cons of each type and how some memory configurations solve the short comings of others.

What Is Memory Partitioning?

Memory partitioning is the system by which the memory of a computer system is divided into sections for use by the resident programs. These memory divisions are known as partitions. There are different ways in which memory can be partitioned: fixed, variable, and dynamic partitioning.

Fixed Partitioning

Let us think about the jewelry box that stores rings. Different pieces of jewelry represent different computer processes. Say you have a jewelry box that displays rings. This box has been partitioned into equal parts.

Figure 1: Ring Display (Illustration: Fixed Partitioning)
illustration:fixed partitioning

Fixed partitioning is ideal for our rings collection provided we always acquire rings with sizes less than these fixed partitions. However, we never have identical jewelry of the same size. Item 1 & 2 fit almost perfectly with little or no wasted space (partition almost the same size as the process). Item 3 however, leaves a lot more space unoccupied (small process in large partition), while item 4 has no partition large enough to fit (large process with unavailable sized partition).

Fixed partitioning is therefore defined as the system of dividing memory into non-overlapping sizes that are fixed, unmoveable, static. A process may be loaded into a partition of equal or greater size and is confined to its allocated partition.

If we have comparatively small processes with respect to the fixed partition sizes, this poses a big problem. This results in occupying all partitions with lots of unoccupied space left. This unoccupied space is known as fragmentation. Within the fixed partition context, this is known as internal fragmentation (IF). This is because of unused space created by a process within its allocated partition (internal).

Variable Partitioning

An alternate solution to address these problems is variable partitioning. In the case of the jewelry box, we anticipate that we possess different jewelry items with different sizes. So, we divide the area of our jewelry box into partitions of different sizes. This way, smaller items of jewelry (small processes) are assigned small partitions while the bigger partitions are saved for the bigger items (large processes).

Figure 2: Illustration - Jewelry Box
illustration:jewelry box

Variable partitioning is therefore the system of dividing memory into non-overlapping but variable sizes. This system of partitioning is more flexible than the fixed partitioning configuration, but it's still not the most ideal solution. Small processes are fit into small partitions (item 1) and large processes fit into larger partitions (items 2 and 3). These processes do not necessarily fit exactly, even though there are other unoccupied partitions. Items 3 and 4 are larger processes of the same size, but memory has only one available partition that can fit either of them.

The flexibility offered in variable partitioning still does not completely solve our problems.

Dynamic Partitioning

Let us examine a typical 64MB space of memory and let's assume that the first 8MB of memory is reserved for the operating system.

64Mb memory space
64Mb memory space

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Additional Activities

Analogy Creation

In this extension, students will demonstrate their understanding of memory partitioning by devising model analogies to represent each type of partitioning.

Step 1

  • Review what you know about the four types of partitioning.
  • Write a brief (single paragraph) summary of the important characteristics of:
    • Fixed partitioning
    • Variable partitioning
    • Dynamic partitioning
    • Compaction

Step 2

  • Now, you will need to consider things in your general environment that behavior or are used in a similar way to each of the partitioning styles.
    • For example, a freezer with ready made drawers for food items is an example of a fixed partition.
    • Variable partitioning could be represented by food storage containers: you tend to try to find a container that will fit the food needing to be saved without wasting too much space.
    • Dynamic partitioning could be related to using flexible bags to store food in a freezer, each bag can be filled or folded to be the exact size needed for the portion of food required.
    • Continuing the food storage example, compaction would be similar to stacking all your stored food to conserve space in the freezer for more containers.
  • If possible, gather items together to have a visual display of these items that represent different partitioning styles.

Step 3

  • Finally, write an explanation for each item explaining what partitioning style it represents and how its function is similar to that style of partitioning.
  • Don't forget to include an introduction explaining partitioning in this document.
  • In each section, discuss the best uses of that kind of partitioning; when it works well and when it doesn't.

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