Computer Science Revision

Computer Science Revision

1. Networks

   • Hardware
     • Hub
       • Cheaper than switches
     • Switch
       • More expensive than hub
     • Servers
       • Email
         • All emails come through this server
       • File
         • All files are stored here
         • They can be accessed by any computer on the entire network
       • Print
         • All printing comes through this server
     • Router
       • Connects the telephone line to the internet
   • Peer to peer
   • Topology

2. Hardware, Software and Storage devises

   • Hardware
     • Something that you can touch
     • RAM,HDD
   • Software
     • A program such as MS Word
     • Not the same as an OS (operating system)
     • MS Office
     • IE
     • MS:E
   • Storage Devises
     • USB
       • Light, portable and virtually inderstructable
       • Large ammoubts of data
       • Upto 128GB
     • Cloud Storage
       • Can be accessed from nearly any devise and can be easily expanded
         • Onedrive
           • Microsoft
         • Google Drive
           • Google
         • Dropbox
         • MEGA Upload
         • iCloud
           • Apple
       • Cheap
       • Virtually Unlimited Storage
     • HDD
       • Used in most desktop PC'S and have a moving component
       • Limited Read - Write Cycle
     • Optical Disc Drive
       • Cheap and can be mass produced
       • Companies are willing to give them away
       • Can not hold alot of data by modern standards
       • Compact
       • 855MB
     • Floppy Disc
       • Widely no-longer used
       • Small ammounts of data
       • Unused by most companies
       • 56MB
     • Tape
       • these are still used by modern companies
       • Used for backup, in high value buissnesses
     • SSD
       • Solid State Drive
       • More expensive than HDD
       • Compacter
       • NO Moving parts
   • Operating Systems
     • Windows
       • 98
       • 2000
       • ME
       • XP
       • Vista
       • Win 7
       • 95
       • Win 8
       • Win 8.1
       • Win 10
     • MAC OS
     • Linux
   • Compression
     • Lossy
       • Lossy is only used on certain files as it will delete some of the files contents
       • It can be used on:
         • Images
         • Sound Files
         • Videos
       • You wouldnt use lossy compression on text and other important documents as it will delete the contents and potentially corrupt the entire document.
     • Lossless
       • Lossy can be used on anyfile as non of the contents are lost. This is most useful with text documents as non of the contents are lost.
       • Lossless compression is usually used in excel files as losing data could be catastrophic for buisness

3. Data Rep.

   • Binary
     • Either a 0 or a 1
     • A 0 or a 1 is 1 bit
     • Appears in a number of bits, 8 bit is the most common in Exams
   • Denary
     • Converted from Binary
     • The value of binary:
       • 128 64 32 16 8 4 2 1
   • Hexadecimal
     • Numbers 1 to 9 are the same
     • Numbers 10,11,12,13,14,15 and 16 are replaced with letters A-F
     • 1,2,3,4,5,6,7,8,9, A,B,C,D,E,F,G
   • Conversions
     • Binary to Denary
       • To convert from an 8 bit binary code to Denary use the table below X 128 64 32 16 8 4 2 1
       • Then add them all together
       • For example
         • Let's convert 1011 1101
         • 128 64 32 16 8 4 2 1
         • 1 0 1 1 1 1 0 1
         • 128+32+16+8+4+1 = 173
     • Denary to Binary
       • Converting denary to binary is essential and relatively easy to do.
       • To convert you have to first find out how many bit binary you are converting to.
       • For this example we will use 8 Bit Binary. We have the number 137 in denary and need to convert to binary
     • https://docs.google.com/presentation/d/13UtH_j0NlyAxtuTKewYBYcYXp4S7fT2GUermPd0pPXM/edit?usp=sharing

4. Data Addition

   • Rules
     • 1+0 = 1 No carry
     • 0+1 = 1 No Carry
     • 0+0=0 No Carry
     • 1+1=0 Carry 1
     • 1+1+1 = 1 carry 1
     • 1+1+0=1

5. Intergrated Developers Enviroment