Modul 2 Sifat Dasar Informasi Digital Mata Kuliah Preservasi Informasi Digital

Outline Representasi Digital 1 Media Fisik 2 Beberapa contoh Riset 3 Catatan: sumber bacaan Bab 2 & 3 [HGS]

Representasi Digital (1/6) Digital Representations of:  Numbers  Text  Images  Sounds  Instructions SINYAL ANALOG SINYAL DIGITAL SINYAL ANALOG

Representasi Digital (2/6)  Representing Numbers  Digital number  base 2 (two symbols 0 and 1)  Each base-2 placeholder represents one binary digit or bit. 8 of these bits equal a byte.  Example: convert the number “ ” in base-2 to base-10 number

Representasi Digital (3/6)  Representing Text  We need: A defined universe, or set, of character An agreed-upon symbol to represent each character  In the computer system, 2 standards are available: IBM’s Extended Binary Coded Decimal Interchange Code (EBCDIC)  used in mainframe computer ANSI (USA)  American Standard Code for Information Interchange (ASCII), 128 characters (original) and then extended to 256 characters.  To convert textual information into computer representation: Match each printed character with a character in the ASCII set Record the associated number from the ASCII character set Store these number in binary form in the computer’s memory

Representasi Digital (4/6)  Representing Images  Basic principle  divide the page into a fine grid of picture elements, called pixels.  The finer the grid, the more image detail resolved  Each pixels  have a value that translates into “degree of grayness or color” Grayscale  several shades between white and black. Ex. 64-level grayscale  64 different shades of gray between black and white Color images  required three numbers: hue (color), saturation (richness of color) and grayscale (darkness or lightness)  Standards: Graphics Interchange Format (GIF)  developed by CompuServe, doesn’t support as many colors as some other file format Tagged Image File Format (TIFF)  developed by Aldus Corp.  for large, high quality or high resolution images Joint Photographic Experts Groups (JPEG)  use a compression scheme that eliminates picture information whose absence our eyes won’t detec

This example shows an image with a portion greatly enlarged, in which the individual pixels are rendered as little squares and can easily be seen.

Representasi Digital (5/6)  Representing Sound  Analog sound must be encoded into digital form to be manipulated by a computer  Encoding process: Sampling Quantization Coding

Representasi Digital (6/6)  Representing Instructions  A program  a set of binary instructions, which computer can follow or execute  Various “language” involved in the process of creating instructions (low level to high level)  Preservation Concerns of computer programs: Preserving the actual program or the functionality of the if the data we trying to preserve will only run using that specific program Preserving the “Documentation”, a code book and other reference material to know how a program is constructed and what it is intended to do

Media Fisik  Two categories:  Magnetic media  Optical media  Magnetic Media  Disk Random access  Tape Serial access

Media Fisik  Magnetic Hard Drive  Tracks are concentric circles around the disk  Sectors are located on the tracks and hold the information  Direct Access Storage Devices (DASD)  14 inch platters, large computer  Redundant Array of Inexpensive Disks (RAID)  multiple hard drives  Types: Removable Hard drives Floppy Disks

Media Fisik  Magnetic Tapes  Two method of stores information Longitudinal recording –Quarter Inch Cartridge (QIC) –Digital Linear Tape (DLT) Helical scan recording –Eight millimeter Data Cartridge –Digital Audio Tape (DAT)

Media Fisik  Optical Media  Use light generated by lasers to record and retrieve information.  Light reflectance characteristics represent “1” or “0”  Disk material with reflectance that can be permanently altered by a laser beam  A laser operating at two power levels: high for recording, low for reading  Altering Reflectance Ablative recording Thermal-bubble recording Dual-allow recording Dye-based recording Magneto-optical recording Phase change recording  Compact Disc CD-ROM CD-R