This week we learned about bit-mapped graphics. Most people will have used a bit-mapped graphic in their life time. They may not realise it but when taking photographs you are storing bit-mapped graphics. Bit-mapped graphics are stored as pixels. Each pixel represents a bit and each pixel can be edited individually which is one advantage of using bit-mapped graphics.
Common file types for bit-mapped graphics are:
- BMP(Bit-mapped Graphic)
- GIF(Graphic Interchange Format)
- JPEG(Joint Pictures Expert Group)
- PNG(Portable Network Graphic)
Each file type uses compression. Compression is when you reduce a file size so the image can be downloaded quicker or you can store more on your device. The two main compressions are lossy and lossless. Other file formats use other compression techniques.
BMP uses RLE(Run-Length Encoding) to compress the file size. GIF’s use LZW (Lempel-Ziv-Welch) compression, JPEG use Huffman Compression and PNG uses lossless compression. When compressing the quality of the image can be affected, this can cause ghosting where the image appears more pixelated in certain areas.
Over the Christmas period I would estimate that I done just over 2 hours of computing revision. During the 2 hours I re-read my notes in my jotter and also read over my blog. The main area’s that I focussed on were the processor, addressability, modularity and the seven stages of software development. I also looked at some past paper questions and answers to see how the questions should be answer and to see if I knew the answers.
Von Neumann Architecture
The VNA has 5 sectors:
- Input Devices
- Main Memory
- Backing Storage
- Output Devices
The CPU contains 3 main specific parts:
- Arithmetic and Logic Unit(ALU) – This is where all the calculations are carried out and where all the logical operations are carried out.
- Control Unit – This manages the fetching, decoding and executing of instructions.
- Registers – These are very fast temporary storage locations which hold; data being processed, instructions being executed, addresses of memory locations to be accesed.
Buses are used to transmit information between the Control Unit, ALU and the registers.
The address bus carries one bit of information on each wire from the processor(MAR) to the main memory. This informs the main memory which memory location will be read or used to store data.
The data bus carries out bit of information at a time on each wire, the information is carried to and from the processor(MDR) and the main memory. This stores data in a memory location and reads data from a memory location
A real number is a number that contains a decimal point. You can not place a decimal point inbetween 1’s and 0’s, so instead we use floating point representation. To do this we find the decimal point and move it over as far to the left as possible.
Now we are left with the whole number, this is known as the mantissa. Count the number of spaces you moved the point, the amount you moved it is called the exponent.
Binary to Decimal
8 Bit binary is set out as follows:
128 64 32 16 8 4 2 1
So the binary code 00101100 would be:
128 64 32 16 8 4 2 1
0 0 1 0 1 1 0 = 32+4+2+1=39
Decimal to Binary
To convert the decimal to binary you take the decimal number, 86. You check to see if 86 goes into 128 but it doesnts. So next you see if 64 goes into 86 and it does, so you take 64 from 86, that leaves you with 22. Check if 32 goes into 22, nope, so does 16 yes, you are now left with 6, then the 4 and 2 go into 6. It should end up looking like
128 64 32 16 8 4 2 1
0 1 0 1 0 1 1 0
They have different measurements so instead of say this storage has so many bytes, instead they can say it contains a Petabyte, which is less confusing.
Why do we use binary?
Its easier for the computers to read, they only have to know 1’s and 0’s instead of more numbers. It also saves electricity because it only needs 2 voltages, one for 1’s and 1 for 0’s.
High Level Language: A high level language is when the code contains lots of English words, and is easy to understand. For example(If, Then, Else). The computer doesn’t understand high level language and then uses a translator to turn the code into machine code(binary).
Low Level Language: This is the complete opposite of a high level language, low level language is written in binary code(0110110) which is easy for the computer to understand but not the reader.
Macros: This is when you record a series of keystrokes which can then be played back as many times as required at a later date. This can save you time, rather than having to do the whole process manually.
Scripting: Scripting is like macro’s except instructions are given in a script or program. These also save time and can help new users to the program preform functions easily.
Parameter: used in a subroutine to refer to one of the pieces of information provided as input to the subroutine.
There are 2 types of parameters:
Actual parameter: When the parameters are passed into the subroutine when it is called from another part of the program.
Formal parameter: parameters which are used in the subroutine definition
A parameter is said to be passed by value if ts value is not changed by a sub routine.
A parameter is said to be passed by reference if the value is changed by the subroutine.
There are two types of subroutine, procedures and functions.
A procedure produces an effect.
A function produces a value.