Memory Read and Memory Write - Fetch Execute

Read Operation
1. Control Unit sets up the Memory Address Register with the locaiton to be accessed
2. Control Unit activates the Read Line on the Control Bus
3. Storage location info are released onto the data bus
4. copy are placed in the Memory Data Register

1. __________________________________________________
2. Control Unit Activates the read line
3. contents are ________________________________________
4. copy of the information ________________________________
5. instruction is decoded and ______________________________


1. same as step 1 in Read Operation
3. contents are transferred via the Data Bus
4. same as our step 3 in Read Operation
5. instruction is decoded and executed!

Write Operation
1. Same as step 1 in read
2. MDR is given the data to be writte
3. control unit activates the write line
4. contents transferred to storage location via the data bus

The Processor

The three parts of the processor - CU A Love U Right!

CU - control unit
* controls the other parts of the processor
* make sure the instructions are carried out in the correct order

ALU - Arithmetic Logic Unit
* carries out calculations
* makes decisions based on logic (AND OR NOT)

R - Registers
* temporary memory locations


Buses - wires that allow data to be transferred

Address Bus -
carries storage locations to be accessed
unidirectional (one direction)
how many locations it can access 2 ^ width
does it affect performance??? - no just makes more locations

Data Bus
bi-directional
carries data back and forth from processor and memory locations
does it affect performance??? - increasing the data bus means you can carry more data per clock cycle, improving performance!

Word size of a computer system??? - (size of the data bus) maximum number of bits the processor can process at one time!

Compression

Lossy - removes parts of the image to reduce the file size, so it has an effect on the image


Lossless - no effect on image, but reduces the file

Advantage of compression?
* takes less time to load image (in browser)
* less memory used
* less time to upload/email

Disadvantages

* takes time to compress images, longer for larger images
* can alter the images, effecting the quality
* repeted compression can ruin the image completely

JPEG - joint photographic experts group
Lossy!!!! -
GIF - graphics interchange format

TIFF - tagged image file format

MPEG - moving pictures experts group

Vector and Bitmap Graphics

BitMap Graphics

Are stored by individual pixels, remember the colour of every individual pixel

* Fixed Resolution, can't be changed on printers etc
* Remembers only the colour of pixel, no layers, objects, moving etc
* can edit individual pixels
* saves the whole screen of the image, even if blank


Vector Graphics

stored as a list of objects and their attributes - e.g. shape, x and y co-ordinates, line thickness, colour

* Resolution Independant, can vary to suit max available on printer
* can't edit individual pixels
* can build up layers of objects, greater flexibility
* can edit individual objects

Effects on Graphic Memory Requirements

adding more to an image???

Bitmap - none, already storing the colour of every pixel
Vector - increases, more objects to store requires more memory

Memory!!!

Big Boys Kicked My Granny Twice!

(starting from smallest)
Bit
Byte
Kilobyte
Megabyte
Gigabyte
Terabyte

ASCII Code and UNICODE

ASCII Code

* ASCII Code uses 7 bit (allowing 128 Characters)
* Extended ASCII uses 8 bit (256 characters)
* Standard File Format
* American Standard Code for Information Interchange

UNICODE

* 16 bit code allowing 65,536 characters

Advantages/Disadvantages
* Unicode requires 16 bits per character, ASCII only 8 bits
* Unicode can represent more characters, allows you to represent more languages

Floating Point Representation (Posse!)

Floating Point RepresentationM and The E

Mantissa = represents the actual number
Exponent = how many places to float the decimal point

MARE!

Mantissa affects the accuracy (more bits = higher accuarcy)
Exponent affects the range (more bits = increased range)