Ch. 7: Storage

Memory sticks and other compact media

(example: micro SD cards, more common to phones, e-readers and cameras) are increasingly versatile and vary in capacity. New gadgets, including a drive that reads micro SD cards and can be inserted like a USB flash drive are now available.

Magnetic Disks

Most common form of secondary storage. Magnetic disk comes in two forms: 1) Hard Disk 2) Floppy Disk Hard disks are (usually but not always) permanently mounted inside the computer. All magnetic disks have magnetically iron oxide coating and read/write heads that can move over the surface of the disk, which is spinning underneath.

Bit

One bit represents one "0/1" switch. lower case b

Byte

One byte represents 2^3 bits=8 bits. A byte is eight bits (a nibble is four bits). A single byte can store a number between 0 and 255 (28-1). upper case B. After that we increment bytes by powers of 10.

CD-ROM

Stands for "Compact Disc Read-Only Memory" and it refers to a CD that can be read by a computer using an optical drive which uses a laser to read the data on the disk. Comes with data already stored on it like a music compact disk. Useful for distributing information that should not be changed (i.e. encyclopedias) and programs (i.e. new versions of software, and games. Typical storage capacity: 650 Mb New technology, known as DVD, will store up 4G per disk. DVD disk drives required to read these disks. Typical data access time: 30-50 milliseconds, although this is steadily improving and should shortly be comparable to magnetic hard disks.

Accessing Data

The concept access time is the time required by the CPU of the computer to access one byte of information on a device for example: hard-drive, CD, DVD, flash drive, etc. It is always good to have fast access time, and it is always measured in milliseconds. -early machines had access time of 88 milliseconds -CD-ROM drive, 200 milliseconds -Today, hard drives have access time of 15 milliseconds or less. -In general, the higher the storage device, the faster the access time.

CD-Rewritable

These are the optical version of magnetic hard disks- that is, data can be written to them and erased from them. Similar in storage capacity and access time to other types of optical disks. Data is written by heating a spot on the disk with a laser beam, in the presence of a magnetic field, the direction of which determines whether a '0' or '1' is written. Data is read by shining a lower power laser beam onto the disk spot (without the magnetic field) and detecting the polarization of the light that is reflected.

DVD

These drives are currently a common option on computers. They often come in combination with a CD-R/W drive; DVD-ROM and DVD-R/W drives are both available. More and more software, especially with complex graphics (particularly games) is distributed on DVD, which have larger storage capacity than CD's. These are currently a common option on computers. They often come in combination with a CD-R/W drive; DVD-ROM and DVD-R/W drives are both available. More and more software, especially with complex graphics (particularly games) is distributed on DVD, which have larger storage capacity than CD's.

Magnetic Tape

This is the oldest, and originally the only, form of secondary storage. It is used, mostly for backup or archival storage, and for batch processing. Data is stored on tracks on the tape-most tape have 9 tracks.

Floppy Diskette

Which today are now phased out. This was one of the first form of storage media. This was an electric medium storage device. Reading from and writing to were both possible. Storage capacity 360K-1.2 MB. Obsolete.

EPROM (erasable programmable read-only memory)

can be erased, usually by exposure to UV light through a transparent window above the chip

Secondary Storage

consists of equipment designed to store large volumes of data for long-term storage. Slow. Non-volatile meaning all data contents retained when power is in the off position. The basic types of secondary storage are: -Magnetic tape -Magnetic disk (``hard'' and ``floppy'') -Optical disk (CD-ROM, WORM, MO).

ROM (Read Only Memory)

contains programs and/or data "burned in" at the time of manufacture. Commonly used to contain programs to "boot up" the computer when it is switched on.

Online or Internet Storage

houses data on computers that act as web servers. Data stored online can then be accessed from any computer with internet access.

Network Drives

located on another computer or a server where space is provided for storage of data from many computer terminals -in a network environment, the designated "server" typically houses "network" drives that allow for both shared access to files among network users, as well as secure back up. -Computers can be attached to the network physically through cable connections, or via wireless connection.

cloud storage

model of networked storage where data is stored in virtualized pools which are generally hosted on one or more web servers. Hosting companies operate large data centers, and users buy or lease storage capacity from them. Physically, the data storage resource may span across multiple servers. The security of the files depends upon the hosting websites. i.e. dropbox

VPN or a Virtual Private Network

provides a secure connection via the internet from any computer to a networked computer. Essentially, this is a service that allows you to operate one computer from another through the internet. When the VPN type of software is housed on a network, you can log in to a computer from another through the internet. When the VPN type software is housed on a network, you can log in to a computer on the network through the internet allowing remote access to networked resources.

Storage

the retention of encoded information over time

Network Storage

variable storage size. Hard disk storage on a remote computer that, by way of a connected network, appears to the user as a local hard disk.

Folders

A folder is a "logical container of files and other folders." It's a "logical" container because the physical disk structure of a folder has nothing to do with the files and folders that are inside. Folders are used to organize the files on a computer into a human-understandable hierarchy. Folders form a tree structure (actually an upside-down tree), starting at the "root" folder.

Kilobyte (KB)

A unit of computer storage equal to approximately one thousand bytes.

Gigabyte (GB)

A unit of storage measuring roughly 1 billion bytes.

Megabyte (MB)

A unit of storage measuring roughly one million bytes.

Terabyte (TB)

A unit of storage measuring roughly one trillion bytes.

compact flash drives

Also known as Thumb drives or USB drives are portable, erasable and re-writable data storage devices. They are small and easily transportable. Not too easily damaged. They attach to your computer through usb ports

PROM (Programmable Read-Only Memory)

Blank ROM chip on which a programmer can write, but only once.

Primary Storage

Connected to the central processing unit (CPU). This is used for temporary storage of data and instructions during processing. Fast. Consists of RAM, ROM, PROM, and EPROM.

Magnetic Floppy Disk

Current size is 3.5" diameter (older floppy disks were 5.25" and 8" in diameter). Organized into clusters, tracks and sectors, like their hard disk.

Drives and Partition

In Windows, when you open "My Computer", you'll see a list of all of the "[disk] drives" that the operating system knows about, helpfully named using a letter of the alphabet (e.g. C:, D:, E:). Windows actually calls these "logical drives". A logical drive can correspond to a physical hard disk, or it may in fact correspond to just part of a disk (a "partition") or even a hard disk that's not actually installed on your PC but is located somewhere on the network. Once a partition is created for your hard drive it is quite difficult to change its size without losing all of the data on the partition.

What are the parts of a magnetic disk?

-Data on the disk surface is recorded on tracks (magnetic, not physical grooves) which form concentric circles on the disk. -Each disk has a set number of tracks. -Tracks with the same number on each disk (recording) surface form a cylinder. -Data is read/written when the required sector on the track rotates into position under the read/write head (note that data can be accessed from any track of the cylinder) -The time taken to position the head over the correct track/cylinder is called the seek time. -The time needed for the sector to arrive (once the heads is in position over the correct tracks/ cylinder is called latency time. -creating the magnetic tracks on a previously blank disk is called formatting the disk.

Computer Care

-First, computers must be kept clean. This means insisting on no food or drink near the computer, and regular cleaning of dusts and debris. -Second, computers should be kept at moderate temperature (between 45 and 85 degrees F). High or low temperatures may damage motherboard memory or disk drive memory. -Third, computers and disks must be kept clear of static. Since information is stored in magnetic fields, static electricity can destroy stored information. Similarly, static electricity can destroy RAM prior to installation in a computer. Computer memory, when shipped, comes packed in static proof wrap. Special care and grounding will minimize the chance that memory will be destroyed during installation. Low static carpeting may be a good investment.

Hard Drive

-The primary storage component of a computer which holds all software and data. -A hard drive has only a few basic parts. They can have one or more shiny silver platters in which the information is stored magnetically. -The interior of a hard drive has an attached arm mechanism that moves a tiny magnet called a read-write head back and forth over the platters to record or store information. -The hard drive uses an electronic circuit to control everything which performs a bridge between the hard drive and the rest of your computer.

File Systems

-a low-level organization of a logical drive's recording surface. Only one filesystem may be installed on a logical drive. "Formatting" is the process used to install a filesystem. -Filesystems allow us to organize our data into files and folders. -Filesystems also provide other attributes that apply to files and folders: read-only, modification date, hidden files, whether the file is ready to be archived

Removable Media

1 MB-800GB Usually a convenient format for transporting or archiving data.

Zip Disks

100 or 250 MB ZIP disks, designed for use in 100 or 250 MB ZIP drives, which could be an external drive, or part of the box.

Random Access Memory (RAM)

128 MB-2GB Data used by currently running programs. Often referred to as "main memory"

CPU Registers & Cache

1B-512KB Temporary and extremely fast storage of program data.

Virtual Memory

256-4 GB RAM data that is temporarily moved to a hard disk to free up memory space. Virtual memory is thousands of times more slow to access than RAM, because it must first be reloaded from the hard disk when accessed.

Fixed Media

40GB-750 GB Almost always consists of one or more hard disks installed in the computer.

RAM (Random Access Memory)

Any location in the memory can be directly accessed in the same amount of time as any other location. Major component of personal computers. Fastest storage device and is accessed at the speed of the microprocessor.

CD-R/W

Compact Disk-Read/Write. -However, care must be taken in selection of type of CD and method of "writing" to the CD-which can also depend upon the type of drive available in your computer. -Some CD's can only be written once, and cannot be erased and overwritten. -Other CD's are designed for re-writing.

Diskette (or "a:" drive)

Has also pretty much phased out. An electronic medium storage device. Reading from and writing to were both possible. Storage Capacity 720 K-1.4 MB