Chapter 4 (Pt. 2)

Each pixel is encoded with either 0 (white) or 1 (black).

• 8 bits can be used to represent 256 different shades of gray • 0 (black) to 255 (white)

16 colors (4 bits per pexl)… use a color palette 256 colors (8 bits per pixel) RGB True Color (Red Value, Green Value, Blue Value) • Typically 8 bits per color (total of 24 bits per pixel) • 16.7 million different colors.

All components of the image are stored Can be easily scaled without losing image quality Common Vector Formats • Adobe Illustrator • CorelDRAW • MathML

Attempt to represent information in ways that preserve accuracy while using significanlty less space.

Measures how much compression schemes reduce storage requirements of data.

Replaces a sequence of identical v1, v2,…,vn by a pair of values (v, n).

• Often used to compress text • More efficient • Can also be used with other forms of data.

• No information is lost in the compression • It is possible to exactly reproduce the original data.

• Do not gaurantee that all of the information in the original data can be fully and completely recreated • Trade image quality for file size

JPEG (Joint Photographic Experts Group) • 8 bit grayscale, 24 bit color • Compression is lossy TIFF (Tagged Image File Format) • 8 bit or 16 bits per color • Compression can be lossy or lossless GIF (Graphics Interchange Format) • 8 bit color palette • LZW lossless compression • Is now patent-free BMP • Uncompressed, large, lossless, simple structure PNG (Portable Network Graphics) • Free open-source alternative to GIF • 8 bit color palette, 24-bit truecolor, 48-bit true color • Compression is lossless • Patent-free replacement for GIF

Computers use binary representation for reasons of reliability. Building a base-10 “decimal computer” • Requires finding a device with 10 distinct and stable energy states that can be used to represent the 10 unique digits (0,1,….,9) of the decimal system. Bistable Environment • Only two (rather than 10) stable states separated by a huge energy barrier.

• No practical universal storage medium exists • All forms of storage have drawbacks • Computer systems contain several kinds of storage

Primary • Directly accesible to the CPU • Relatively expensive • RAM (volatile) … access time in nanoseconds • ROM (non-volatile) • Contains a small startup program (BIOS) • Reads a larger program from non-volatile secondary storage to RAM and start to execute it. Secondary • Not direclty acessible by the CPU • Relatively cheap • Non-volatile

Hard disk drives … access time in milliseconds Rotating optical storage devices • Longer access times than hard disk drives • CD drive • DVD drive Flash Memory • USB Flash drives • SD cards • Memory Stick (Sony) Solid State Drives Hybrid Drives

• As primary memory fills up, the least-used data is moved to secondary storage devices (swap file) • This data is retrieved when needed • More retreivals mean overall system performance is degraded

• Storage that can be physically removed or disconnected • Inreases general information security • Useful for archiving data

• Volatility • Mutability • Accessibility • Addressability • Capacity • Performance • Energy Use

• Retain stored information without power • Suitable for long-term storage

Requires constant power to maintain stored information Types • Dynamic Random-Access Memory (DRAM): requires stored information to be preriodically re-read and re-written (refresh) or it will be lost • Static Random-Access Memory (SRAM): does not need to be refreshed as long as power is applied.

Read/Write Storage • Allows information to be overwritten at any time • Example: RAM, hard disk drives

Read Only Storage • Retains information stored at the time of manufacture Write Once Storage • Allows information to be written only once at some point after manufacture • Example: CD-R

Allows information to be overwritten multiple times, but with the write operation being much slower than the read operation. • Example: CD-RW and Flash Memory

• Any location in storage can be accessed at any moment in approximately the same amount of time • Most semiconductor memories and disk drives provide random access.