OS Chap 2

• Bit

  Basic unit of data representation
• Grouping bits

  1. Bits are grouped to form bytes

  2. Bytes are grouped to form words
• Byte

  Group of bits
• Word

  Group of bytes
• Basic elements of computer system

  • Memory
  • Processor
  • I/O Unit
• Bits


  Patterns of 0s and 1s used to encode computer information
• Bits can represent numeric values, characters, images, or sounds depending on the application
• Memory cell


  Manageable unit of memory, typically 8 bits (1 byte)
• Memory

  • Holds active programs and data
  • Program must be stored in memory before execution
  • Data must be stored in memory before manipulation
  • Memory write is destructive
  • Memory read is not destructive
  • Bytes or words are the basic addressable units
• Memory address

  Number that identifies a specific memory location
• If a memory has n locations, they will have addresses 0 to n-1
• All locations in memory contain the same number of bits
• Memory address length

  Determines the number of unique memory locations that can be addressed
• Memory cell length


  Number of bits that can be stored in each memory location
• Memory Address Register (MAR) holds the address of the memory location to be accessed
• Memory Data Register (MDR) holds the data to be written to or read from memory
• Address decoder translates the address in MAR into signals to access the specific memory cell
• Fetch


  Instruction to read content of a memory location
• Store


  Instruction to write a value to a memory location
• Cache memory


  • Quickly accessible memory that stores frequently used data, closer to the CPU than main memory
• Program


  Series of instructions executed by the processor
• Instruction


  Has an operation code and one or more operands
• Processor components


  • Instruction control unit
  • Clock
  • Registers
  • Arithmetic and logic unit
• Input/Output Control System (IOCS)


  • Communicates directly with peripheral devices
  • Accepts logical I/O requests from application programs and generates primitive commands to control devices
• Logical I/O


  The programmer's view of I/O, one logical record
• Physical I/O


  The transfer of a physical record between memory and a peripheral device
• Word size


  The common size of internal components, affects processing speed, memory capacity, precision, instruction set size, and cost
• Larger word size


  Faster processing speed
• Larger word size


  Greater memory capacity