Understanding Data Storage: Media, Devices, and File Systems - Prof. Willis Boughton, Study notes of Computer Science

Download Understanding Data Storage: Media, Devices, and File Systems - Prof. Willis Boughton and more Study notes Computer Science in PDF only on Docsity!

Chapter 3

1

Storage medium (what data is stored on)

Floppy disk, CD or DVD, etc. Can be removable or nonremovable from the storage device

Storage device (device into which storage medium

is inserted to be used)

Floppy disk drive, CD or DVD drive, etc. Devices on Microsoft Windows are identified by name or letter a: device is floppy c: device is main disk drive Can be internal, external, or remote

Storage is nonvolatile

When power to the device is shut off, data stored on the medium remains This is in contrast to RAM, which is volatile

Access (usually random but can be sequential)

Random access: data can be retrieved directly from any location on the storage medium, in any order Also called direct access Floppy and hard disk drive Sequential access: data can only be retrieved in the order in which it is physically stored on the medium Keyboard and tape drive

Logical file representation (logical file system): refers

to the user s view of the way data is stored

What you see in Windows Explorer File: something stored on a storage medium, such as a program, document, or image Filename: name given to a file by the user Folder: named place on a storage medium into which files can be stored Shortcut (Microsoft Windows): a file that is a link to another file (an "alias" for another file)

Physical file representation: physical way the data is

stored on the media as viewed by the computer

Magnetic:

Data is stored magnetically; the data (0s and 1s) is represented using different magnetic alignments Floppy and hard disk

Optical:

Data stored as optical marks made by laser beam CDs and DVDs

Electronic:

Data stored electronically Flash memory (called memory but in fact is storage)

Magnetic disk: storage medium that records data

using magnetic spots on circular platters (individual

disks) made of flexible plastic or rigid metal

Platters spin while data read or written

Most widely used storage medium

Floppy disks:

Removable storage medium no longer widely used Disk has only one slow-spinning platter

Hard disks

Main storage device on all PCs Disk has several fast-spinning platters

Low capacity, random access, removable magnetic

disk made of flexible plastic permanently sealed

inside a hard plastic cover

Only 1.44 MB capacity Very slow

Floppy disk drive: storage device that reads from

and writes to floppy disks

Sometimes referred to as a legacy drive and not

included on all new PCs today

Can buy external floppy drive and connect via USB

Consists of one or more metal magnetic platters with

an access mechanism

Each platter has read/write heads, usually one on

top and one on bottom (2 heads per platter)

Heads move very quickly back and forth across platters to read and write data

Platters are permanently sealed inside the hard

drive to avoid contamination and to enable the

platters to spin faster

Typically more than 5000 rpm The faster the spinning, the faster the data transfer

Disk access time: time that it takes for a drive to

start to read or write a file

Depends on how fast the disk spins and how fast the read/write heads can move Typically about 10 ms (0.01 sec)

Hard disk cache: RAM used to temporarily store

data being read or written

Greatly improves disk performance since data already in cache can be retrieved much faster RAM is on the motherboard or disk adapter card - not main memory

Dividing one hard disk into separate areas called

partitions or logical drives

One disk could have c:, d:, and e: drives, for example

Used for:

Installing more than one operating system Creating a recovery partition - restore system if main partition becomes unusable Creating separate partitions for programs and data

Partitions demo

External hard drives: connect to an external port,

usually USB, FireWire, or PC Card

Drive can be moved from one PC to another Good for backup purposes May be slower and less reliable than internal drive

Portable hard drives: designed to be carried around

Good for backup purposes Less capacity and more expensive

Either external or portable likely will break if dropped