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... ems you will often encounter data that is in EBCDIC. This Character code will be displayed when data is being transferred between PCs, the characters will be printed to the screen as the data arrives at the receiving terminal. Memory requirements To output an image on a display the computer must have a video card that has memory on it, the memory is where whatever is to be displayed is stored. The larger the resolution of the picture to be displayed, the more memory is required. The memory that is on video cards is a lot faster then that of what is used but the computer itself.
The reason for this is that a lot of processing has to be done by the card to keep the display updated i. e. moving the mouse cursor around. Due to this large amount of data movement it is necessary for the memory to operate at very high speeds so that the through put to the display is constant.
Generally monitors have around 32 mb of super fast memory on them now, this allows large images to be worked with and also allows 3 D imagery to be produced and stored on the video card itself. Cylinders A cylinder is the name given to the data area on a disk platter, a disk may have a few platters, these are like circular disks stacked on top of each other. If a hard drive has 4 platters, and each platter has 600 tracks then it can be said that there are 8 tracks in the cylinder. The reason these tracks are grouped into cylinders is because each platter will have its own read and write head on each side of the disk surface, hence as the disk rotates it will be able to read and write to 8 places at the same time. These are simultaneously written on, on the top and underside of each of the four disks.
Sectors A sector on a disk is a data location that has its own specific reference number, this number is used to recall data stored at this sector. A sector is a singular part of a data track. An example of this maybe if a disk has 80 tracks and each of these data tracks maybe divided up into 20 sectors, a sector is the smallest size chunk of data that a hard disk can access. A track would look like the black circle show above, then this track would be further broken down into sectors by dividing up the disk, a bit like cutting a cake into equal parts (see below). The problem with the cake slicing style method is that sectors near to the centre of the disk are fairly small, where as the outer tracks on the disk have much larger sectors. These larger outer tracks are wasting disk space as a lot more sectors could easily be fit in this space.
It is however possible to use a different method to divide the tracks up into sectors, this is called zoned-bit recording, this method allows the outer tracks to contain more sectors then what is in the centre tracks. File allocation unit The file allocation unit is the smallest size block of space allocated for saving too. The size of the file allocation unit varies between disks of different sizes. For example a disk that has a capacity of less then 32 mb, then the allocated minimum size of the unit will be 512 bytes per sector. For larger disk sizes the file allocation unit increases. A 64 mb disk partition will have an allotted size of 1 K, a 128 mb disk will have a 2 K unit and a 256 mb disk, 4 K.
The problem of this is that when small files are saved, say less then 2 K on the 256 mb drive, whatever the remained of the 4 K sector that is not used will be wasted. So in theory the same number of < 2 K files will be able to be saved on the 256 mb disk as the 128 mb one as the sectors are not being fully used. When a file is stored the system will allocate certain sectors for the data to be stored at and then record these sectors reference number. It can be said the smaller the allocation unit is, the less disk space will be wasted. But, it can also be said that the larger the allocated size is the smaller the TOC will be (as there will be less sectors to reference) thus leaving more of the disk space to be used for data storage. Directory entry contents The directory contents are used to store the where about of all files saved on the disk.
The directory will house the path of where the file should be shown, i. e. what folder it should be located in. All files that are saved on the disk will be logged here so that the system knows where they are located on the disk and also what cluster to find them on. Paths Paths are routes that take the user to a certain folder or file. A path to a file may look like this: C: windowstempinstallAdobeinstall.
exe. This path points at an executable file that is contained inside a series of folders. As the first folder is opened a few more folders will be available to the user, the user will have to visually find the next folder that contains the file and opened that then repeat this process until the required file is found. It is important to know where files are saved in order to access them again. If a file is saved without the user seeing where the file was saved it can often cause problems locating this file again. File allocation tables A file allocation table or FAT for short is used to keep a reference of where the data for a file is saved on a hard disk.
The FAT table is a chart of numbers that correspond to cluster addresses on the disk. When the user or a program requests a file the FAT is searched to find the address of the clusters that the file is saved in. Once this is done the hard disk will be able to send the requested data to the OS. So basically the file allocation table is like an address book that holds the location on the disk of all the data stored. Fragmentation Fragmentation is when a file can not be saved on consecutive clusters and is forced to be saved in different parts of the disk.
In other words the file is cut into fragments and saved in many different locations on a disk. Normally the problem with this is that is will slow down the performance of the disk as the read / write heads will have to move from one location to the next to reassemble the file in whole...
Free research essays on topics related to: read and write, disk space, video card, hard disk, 2 k
Research essay sample on Read And Write Disk Space
