Computer data storage

Functionality and Types of Storage - Computers without memory can only perform fixed operations and immediately output results - Von Neumann machines have memory to store operating instructions and data - Von Neumann machines can be reprogrammed with new in-memory instructions - Von Neumann machines are more versatile and simpler to design - Most modern computers are Von Neumann machines - Computers represent data using the binary numeral system - Information can be converted into a string of bits - The byte is the most common unit of storage, equal to 8 bits - Data are encoded using various standards (e.g. ASCII, JPEG, MPEG-4) - Redundancy allows computers to detect and correct errors in coded data - Storage is divided into primary, secondary, tertiary, and off-line storage - Primary storage is semiconductor storage directly accessible by the CPU - Secondary storage consists of storage devices not directly accessible by the CPU (e.g. hard disk drives, optical disc drives) - Tertiary storage refers to storage used in robotic tape libraries - Off-line storage is the furthest from the CPU and has the lowest bandwidth - Primary storage includes memory such as DRAM - Secondary storage includes non-volatile devices like hard disk drives - Primary storage is directly accessible to the CPU for executing instructions - Early computers used delay lines, Williams tubes, and magnetic drums as primary storage - Semiconductor memory became dominant in the 1970s, leading to modern RAM Memory Hierarchy - Processor registers are located inside the CPU and hold a word of data - CPU instructions manipulate data stored in registers - Processor cache is an intermediate stage between registers and main memory - Main memory, such as RAM, is used for storing opened programs and as a disk cache - Spare memory can be used as a RAM drive for temporary high-speed data storage Introduction to Computer Data Storage - Computer data storage is introduced to improve the performance of computers. - Cache memory is faster but has lesser capacity compared to main memory. - Main memory is slower but has greater storage capacity than processor registers. - Multi-level hierarchical cache setup is commonly used, with primary cache being the smallest and fastest. - Main memory is connected to the central processing unit via a memory bus, consisting of an address bus and a data bus. Characteristics of Storage - Volatility: Determines whether the stored information is retained without constant power supply. - Mutability: Describes the ability to overwrite information at any time. - Accessibility: Refers to the ease of accessing any location in storage. - Addressability: Determines how information is selected and accessed within storage. - Capacity: Represents the total amount of information that a storage device can hold. - Mutability: Read/write storage, slow write/fast read storage, write once storage, read only storage - Accessibility: Random access, sequential access, addressability (location-addressable, file addressable, content-addressable) - Capacity: Raw capacity, memory storage density, performance, throughput, granularity Storage Media - Semiconductor: Uses integrated circuit chips to store information, with both volatile and non-volatile forms. - Magnetic: Includes hard disk drives, magnetic tape, and carousel memory, used for primary, secondary, and tertiary storage. - Optical: Utilizes technologies like Ultra Density Optical (UDO), magneto-optical disc storage, and 3D optical data storage. - Flash Memory: Gains popularity as off-line storage for home computers, often used in solid-state drives (SSDs). - Paper: Traditional form of data storage, including paper tape, punched cards, and barcodes.