IES070101-tutorial5

Find an image, description, examples and advantages for each of the following:

1. Magnetic Disk

2. Optical Disk

3. Flash Memory

4. Magneto-optical Disk

Magnetic disk

Magnetic disc use magnetic particles that coated the surface to store items, data, instruction, and information. Like tape, it is magnetically recorded and can be re-recorded over and over. Disks are rotating platters with a mechanical arm that moves a read/write head between the outer and inner edges of the platter's surface. It can take as long as one second to find a location on a floppy disk to as little as a couple of milliseconds on a fast hard disk.

Example:

Fixed hard disk

Zip removable disk

Floppy disk

Pocketzip

Advantage:
1. The advantages magnetic disk include the ability to write/record and read data very rapidly. 2. Data that is no longer needed can be erased to make space available for new data.
3. The number of images that can be stored on a magnetic disk depends on the numerical size of the images and the disk capacity.
4. The capacity (Megabytes) of a specific disk size is determined by how small the individual bit areas can be made.

Optical disk

An optical disk is a type of storage media that consist a flat, round, portable disk made of metal, plastic, and laquer that is written and read by laser. It is primarily store software, data, digital photo, movies, and music. Some of it are read only, and read and write. The optical disk includes a stiffening layer having two spaced-apart surfaces, the stiffening layer having a specific stiffness selected to be greater than 1*108 inches and being positioned at the center of the thickness of the optical disk. The optical disk further includes first and second recording layers, each recording layer being formed over opposite surfaces of the stiffening layer, and first and second substrates being formed over the first and second recording layers, respectively.

Example

CD-ROM

DVD-R/CD-RW.

Advantage:
1. Reliable for long term storage.

2. The high capacity and low cost per unit of data stored make optical media an effective storage solution.

Flash memory

Flash memory card are a type of solid-state media that means they consist entirely of electronic components and contain no moving parts. Flash memory is non-volatile memory computer that can be electrically erased and reprogrammed. It is a technology that is primarily used in memory card and USB flash drives for general storage and transfer of data between computers and other digital products.

Example

USB Flash Drive

Memory Card

Advantage
1. Flash memory has no moving parts and can be more durable.
2. It can use less power.

Magneto optical disk

A type of disk that combines magnetic disk technologies and CD-ROM technologies. A magneto-optical drive is a kind of optical disc drive capable of writing and rewriting data upon a magneto-optical disc. These drives use a hybrid of magnetic and optical technologies, employing laser to read data on the disk, while additionally needing magnetic field to write data. An MO disk drive is so designed that an inserted disk will be exposed to a magnet on the label side and to the light (laser beam) on the opposite side. The disks, which come in 3.5in and 5.25in formats, have a special alloy layer that has the property of reflecting laser light at slightly different angles depending on which way it's magnetized, and data can be stored on it as north and south magnetic spots, just like on a hard disk.

Example

WORM

Advantage
1. Induced super resolution' (MSR), heat distribution and magnetism within the laser beam enable MO drives to read data that is smaller than the beam spot size, enhancing storage density
2. Magneto-optical disks, such as the rewritable optical disk and the recordable disk used with the Mini Disc player, have a special layer, as of barium ferrite, that can be magnetically polarized by a recording head when heated with a laser. Data or sound may be recorded to and erased from any portion of a magneto-optical disk multiple times.

IES070101-amali4

Comparison between Windows and Linux in implements virtual memory:

Window	UNIX/Linux
Window use the term swapping to differentiate from general paging, and call the dedicated secondary store just a page file.	In Linus swapping only refers to virtual memory scope and paging to both. Page in is transferring a page from the disk to RAM. Page out is transferring a page from RAM to the disk. But swap in and out only refer to transferring pages between RAM and dedicated swap space or swap file, and not any other place on disk.
In window the file used for paging is named pagefile.sys. The default location of the page file is in the root directory of the partition where Windows is installed. Windows can be configured to use free space on any available drives for pagefiles. It is required, however, for the boot partition (i.e. the drive containing the Windows directory) to have a pagefile on it if the system is configured to write either kernel or full memory dumps after a crash. Windows uses the paging file as temporary storage for the memory dump. When the system is rebooted, Windows copies the memory dump from the pagefile to a separate file and frees the space that was used in the pagefile.	It use the term "swap" to describe both the act of moving memory pages between RAM and disk, and the region of a disk the pages are stored on. It is common to use a whole partition of a hard disk for swapping.Linux supports using a virtually unlimited number of swapping devices, each of which can be assigned a priority. When the operating system needs to swap pages out of physical memory, it uses the highest-priority device with free space. If multiple devices are assigned the same priority, they are used in a fashion similar to level 0 RAID arrangements. This provides improved performance as long as the devices can be accessed efficiently in parallel. Therefore, care should be taken assigning the priorities.
Windows 2000, XP, and Vista offer the DisablePagingExecutive registry setting, which controls whether kernel-mode code and data can be eligible for paging out.	Linux offers the /proc/sys/vm/swappiness parameter, which changes the balance between swapping out runtime memory, as opposed to dropping pages from the system page cache.
Windows makes heavy use of the working set concept. The working set is defined as the amount of main memory currently assigned to the process, so the working set consists of its pages that are present in the main memory. The size of the working set is, however, not constant. So the disadvantages that come with working sets are heavily reduced.	Linux used NRU algorithm for page replacement, but due to the various shortcomings of the algorithm, they have changed it and implemented an approximate
Windows NT and its variants employ a dynamically allocated pagefile for memory management. A pagefile is allocated on disk, for less frequently accessed objects in memory, leaving more RAM available to actively used objects	Most hard drive installations of Linux utilize a "swap partition", where the disk space allocated for paging is separate from general data, and is used strictly for paging operations.

Reference:

1.http://en.wikipedia.org/wiki/Paging

2.http://www.faqs.org/docs/linux_admin/x1762.html

3.http://gaurang.org/academics/csci555/termpaper2.pdf

4.http://www.experts-exchange.com/OS/Miscellaneous/Q_21365611.html