Computer Science

Computer Science

1. CPU

   • Fetch Decode Execute
     • Registers
       • Small block of memory but fast memory
         • PC
           • Holds the next instruction to be fetched from RAM
         • MAR
           • Holds the current instruction about to be fetched
         • MDR
           • This stores the data that was read or written from memory
         • Accumulator
           • Results from the ALU are stored here temporarily before being stored in memory
   • ALU
     • Arithmetic logic unit
       • Preforms all of the mathematical and logical calculations in the CPU

2. Operating system

   • Memory management
     • Operating systems decide what goes where in memory
     • Makes sure memory is used efficiently
     • Makes sure data isnt overwritten
     • Memory is divided into pages
   • Virtual Memory
     • It uses secondary storage to hold parts of the program that aren't currently needed
     • Slower to access than main memory(RAM)
     • Loaded to memory and run as a process. Needs to be moved back into RAM to run
     • CPU remembers where everything is stored. Read and Write
   • Fragmentation and Defragmentation
     • Files are usually split into blocks across many segments