Memory and storage Study Guide

Secondary storage, also known as auxiliary storage or external memory, refers to non-volatile storage devices that are not directly accessible by the CPU. Unlike volatile primary storage (RAM), secondary storage retains data even after the power is turned off. Its main purpose is to store data and programs persistently and in larger quantities than primary storage. Examples include Hard Disk Drives (HDDs), Solid State Drives (SSDs), and various forms of optical and magnetic media. Each type of secondary storage has different characteristics concerning capacity, speed, portability, durability, and cost per gigabyte, making them suitable for different applications. For instance, HDDs offer large capacity at a lower cost, suitable for archiving, while SSDs provide faster access times, ideal for operating systems and frequently used applications. Optical discs are good for portable read-only data, and magnetic tapes are used for mass backup due to their high capacity and low cost, despite slow access. Understanding these differences is crucial for selecting appropriate storage solutions.

Data compression is a crucial technique used to reduce the size of files, making them easier to store and transmit. When a file is compressed, its original data is encoded into a smaller format, which then needs to be decompressed to restore it to its original or near-original state. There are two primary types of compression: lossless and lossy.

Lossless compression algorithms reduce file size without losing any data. This means that when a file is uncompressed, it is an exact replica of the original. Examples of lossless compression include ZIP, PNG (for images), and FLAC (for audio). This type is essential for data where accuracy is paramount, such as text documents, executable programs, and medical images.

Lossy compression, on the other hand, reduces file size by permanently removing some information that is deemed less important or imperceptible to humans. While this results in significantly smaller file sizes, it means that the decompressed file is not an exact match to the original. Examples include JPEG (for images), MP3 (for audio), and MPEG (for video). Lossy compression is commonly used for multimedia files where a slight reduction in quality is acceptable for the benefit of smaller file sizes and faster streaming or download times. The choice between lossless and lossy compression depends entirely on the application and the acceptable trade-off between file size and data integrity.