The Nature Of Digital Information

Digital Representation

• Numbers• Text• Images• Sounds• Instructions

Representing Numbers

Menggunakan satuan, puluhan, ratusan, ribuan, dstBasis 10Basis 2?100101 = [(1) × 25] + [(0) × 24] + [(0) × 23] + [(1) × 22] + [(0) × 21] +

[(1) × 20] =[1 × 32] + [0 × 16] + [0 × 8] + [1 × 4] + [0 × 2] + [1 × 1] = 37

Representing TextMembutuhkan 2 hal:• A defined universe, or set, of characters to

represent. (angka, huruf, tanda baca, titik, dsb)

• An Agreed-upon symbol to represent each character in the set.

• Standards computer codes:– Extended Binary Coded Decimal Interchange Code

(EBCDIC)– The American National Standards Institute (ANSI); issued

American Standard Code for Information Interchange (ASCII)

• 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

Exp:cat

c = 1100011, a = 1100001, t = 1110100

• Unicode• Digunakan dalam Win95, Win 98, dan NT. Juga

office 95 dan 97

Representing Images:

• Dibagi menjadi ‘pixels’• Value dari Pixel:– Grayscale– Color images (hue, saturation, grayscale)

Standard file format:• GIF• TIFF• JPEG

Representing Sound

• Encoding process:– Sampling– Quantization– Coding

Representasi Digital

• 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 program 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

• 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

Types of Digital Objects

• Simple vs. Composite• whether they normally are treated as a Whole

whether they are normally treated as a collection of simpler parts

• if we can break the preservation challenge of a composite object into smaller components then it will make the preservation task easier

Rendered vs. Non-rendered• processed by some software to produce a

rendering which is presented to a human user who can then interpret what he/she sees/hears/feels/tastes. This can include documents, pictures, videos and sounds

• one can have a digital object for which it is not enough to simply render it but for which one needs to know what the contents mean in order to be able to further process it.

Observations of the Earth from space, including multi-spectral images, syntheticaperture radar images Measurements of the atmosphere, chemical or electrical composition

Static vs. Dynamic• Static objects are ones which, unless they are

transformed, are unchanged as bit sequences. These we will refer to as Static Digital Objects.

• Alternatively we can consider a whole collection of files as the data object. Such a collection might change as additional files are added to the collection over time. Such digital objects we will refer to as Dynamic Digital Objects.

Active vs. Passive• Passive Digital Object we mean something

with which things are done, for example used by other applications (software) to do something.

• Active Digital Object on the other hand does something. For example the word processing application

Multiple-Classifications