CS 3303-01 Data Structures - AY2022-T5
Dashboard My courses CS 3303-01 - AY2022-T5 28 July - 3 August Learning Guide Unit 7
Learning Guide Unit 7
Unit 7 Learning Guide
Overview
Unit 7: File processing and external storing Topics:
Primary versus secondary storage Disk drives: architecture and access costs Buffers and Buffer Pools External Sorting
Learning Objectives:
Understand and be able to articulate the differences between primary and secondary storage including: o Computer RAM memory o Disk drives and other secondary storage devices o The concepts of persistent versus volatile memory o Data structures implemented in secondary storage (file structure) Understand the terminology and architecture of disk drives Understand the concept of disk access costs associated with head movement and seek time Understand and be able to implement a buffer cache that incorporates concepts such as: o Buffer pool oHeuristics including FIFO, LFU, and LRU approaches
: Virtual memory
Understand and be able to implement External sorts and be familiar with key concepts including: o Key sorts and index files o Quicksort and mergesort implementations : The replacement selection algorithm o Merging Introduction
In unit 7, we explore file processing and external sorting algorithms. It is important to understand what differentiates internal storage form external storage to understand why we have both internal and external storage and when it is important to use each. Internal storage, which is what all of the algorithms and data structures that we have dwelt with so far have used, is the internal memory (often referred to as RAM or random access memory) of the computer. This memory is very fast. Although the actual speed of memory varies from one computer to the next, suffice it to say that RAM is orders of magnitude faster than external storage. External storage, on the other hand, doesn't have as much performance, but it does have characteristics such as size and persistence that make it equally as important as internal storage. The following table compares internal and external storage and begins to show why each is so important.
Internal Storage
External Sto
Very fast 100,000 to 1,000,000 times as fast as external storage Cost is high per unit of storage is high when compared with external storage Quantity of storage is relatively low when compared with External storage Data stored is not persistent ... when the power is turned off the data is lost
Slower performance when con Cost per unit of storage is rela Size of storage is virtually unli Data stored is persistent as it s until erased
By considering these characteristics we can come to some conclusions. First since internal storage is so much faster than external storage operations that require a lot of storage access will be faster when using internal storage. Sorts conducted in internal storage are much faster than those that must access external storage. In our text, Shaffer leads us to an understanding of disk drive technology, which is the most common form of external storage. Key topics that are introduce