Storage Devices PDF

Storage Devices 1  Memory (3 types of memory) ROM (Non-Volatile) Read Only Memory (We can only read the system files, process using them, and cannot update them. Secondary Memory (Non-Volatile) Data can be stored without power. (Hard Disk) 2 ㅡ RAM (Vola...

Storage Devices 1  Memory (3 types of memory) ROM (Non-Volatile) Read Only Memory (We can only read the system files, process using them, and cannot update them. Secondary Memory (Non-Volatile) Data can be stored without power. (Hard Disk) 2 ㅡ RAM (Volatile) 8 Primary Memory or Main Memory or Cache. Temporary store the data during power on. Secondary Storage Secondary storage is often referred to as ‘storage’. However, it should not be confused with primary storage or main memory, ✓However, which areitterms should not be used sometimes confused to referwith primary to Random storage Access or (RAM) Memory or Read Only Memory (ROM) Secondary storage is non-volatile, which means it will not lose data when the system’s power is turned of. 3  Secondary Storage (Cont’d) Secondary storage is used for: 01 storing a document for future use 01 02 storing an application, ready to be loaded into RAM when the user opens the application 03 Virtual Memory space on a computer for storing instructions and programs until they are needed or being used 4  Devices Storage devices are used to store data or software that is used in a computer system. Internal Storage Devices External 5 Devices (Cont’d) Figure: Storage can be internal or external 6  Devices (Cont’d) the circuit in a computer with connectors to which other components connect Internal Drives Connect directly to the computer’s motherboard External are connected to the computer’s motherboard through the different Devices ports and adapters on the computer’s exterior. 7  Devices (Cont’d) A Storage device contains the storage media and accesses the data stored on it. Access the data Storage Media stored on it Flash USB drive Memory DVD Disk DVD drive 8  Different types of storage device 1. Hard Disk Hard disk drives (HDD) contain hard disk media. The drives provide a connection from the disk to the motherboard, either directly or using a wireless adapter like Wi-Fi or a wired port like USB. 2. SSD Solid state drives (SSD, often referred to as flash drives) contain flash memory media. They are otherwise identical to hard disk drives. 9  Different types of storage device (Cont’d) 3. Optical Disk Optical disk drives contain optical disk media. Newer drives are often compatible with older media. For example, a disk drive that can read Blu-ray media can also read DVD and CD media. This is known as backwards compatibility. the ability to be used with older technology without having to be specially adapted 10  Media-Hard disks Circular plate Hard disks are made up of many concentric platters. These platters make up a cylinder that spins on a central spindle. A read/write head moves on an arm across tracks on the platter. the part of a disk drive The amount of time that it takes the read/write head to that passes across (or access data on the tracks is determined by how fast the floats) the platters on a very thin layer of gas cylinder of platters spins and how fast the read/write head above the platters is moved across the tracks. 11  Media-Hard disks (Cont’d) When reading, a read/write head changes the magnetic field into electrical current. When writing, it transforms electrical current into a magnetic field. Typical spin speeds are 5400 revolutions per minute (rpm) or 7200 rpm. Figure: Read/Write heads move across a hard disk The average seek time for a read/write head is platter to access data as 4-15 milliseconds(ms). the cylinder spins the time it takes for a read/write head to locate the area on the disk where the data to be read is stored Hint: If a read/write head crashes into a platter, it can cause damage to data and the 12 platter. This would not happen with a solid drive.  Optical media CD Types of Optical Media DVD Blu-ray Disk 13  Optical media (Cont’d) CD CDs can store up to 700 MB of data. The data is written to the disk using a laser, which writes data to a plastic layer beneath layers of aluminum and acrylic. 14  Optical media (Cont’d) DVD DVDs look very much like CDs. Data is written to DVDs using a shorter wavelength of red laser light, which allows DVDs to store more data. They can store 4.7 GB on a single-sided, singer-layer disk. Double-sided, dual-layer disks can store as much as 18 GB. 15  Optical media (Cont’d) Blu-ray Disks Blu-ray disks are similar to CDs and DVDs, but use a scratch-protection coating. Violet laser light is used to store data at greater density than the red laser light used in DVDs. They can store 25 GB on a single-sided disk, and double-sided disks can store 50 GB. 16  Optical media (Cont’d) All optical media is recordable and is known as CD-R, DVD-R or BD-R. Some CDs and DVDs can be rewritten (CD-RW, DVD-RW), and some Blu-ray media can be written then erased and Figure: Comparison of various lasers used to rewritten (BD-RE). store data on optical media 17  Flash media Flash media are more energy-efficient than hard disks as they do not have moving parts. For the same reason, they are also less likely to fail when they are moved around. This makes them suitable for use in portable devices. 18  Magnetic tape Magnetic tape was originally designed to record sound, but it is now also used to store data. Figure: Magnetic tape is mainly used for backing up data in large organizations 19  Hard Disk Flash Media Optical Magnetic Media Tape Data Access Fast Fastest Slow Slowest Speed Maximum Varies, up to Varies, up to CD 700 MB Varies, up to Capacity 128 GB many TB DVD 18 GB 185 TB Blu-ray 50 GB Cost per GB High Very high Medium Low Use Servers, Laptops, Multimedia Whole system personal mobile (music, backups and computers, devices games and archives backups films), file backups Portability Not suitable Yes Not suitable Not suitable 20  Vocabulary Data access speed: how quickly data can be read from or written to media Capacity: the amount of data that can be stored on media bit (binary digit): a single unit of information with a value of either 0 or 1; eight bits equal one byte 21  Storage Devices Storage media store data in binary form. This means that each bit of data holds one of two values: 0 or 1. Different media types interpret 0 or 1 differently. Hard disks change the magnetic charge of a platter to either negative or positive, depending on whether the value is 0 or 1. Optical media use tiny bumps on the disk’s surface to represent 0 and 1. Flash media use different levels of electrical charge, held in tiny individual cells, to represent 0 or 1. Magnetic tape changes the magnetic charge of the tape to either negative or positive, depending on whether the values is 0 or 1. 22  Units of Storage Capacity Number of Bytes With unit Name symbol 1,000 1 KB Kilobyte 1,000,000 1 MB Megabyte 1,000,000,000 1 GB Gigabyte 1,000,000,000,000 1 TB Terabyte 1,000,000,000,000,000 1 PB Petabyte 1,000,000,000,000,000,000 1 EB Exabyte 1,000,000,000,000,000,000,000 1 ZB Zettabyte 1,000,000,000,000,000,000,000,000 1 YB Yottabyte 23 24 25