memory bits bytes
Download
Skip this Video
Download Presentation
Memory, Bits, & Bytes

Loading in 2 Seconds...

play fullscreen
1 / 10

Memory, Bits, & Bytes - PowerPoint PPT Presentation


  • 93 Views
  • Uploaded on

Memory, Bits, & Bytes. Memory. Part of the computer where programs and data are stored. Read and written (changed). Bit Binary digit Basic unit of memory 1 or 0 Why binary? Because we can most reliably (electronically) distinguish between 1 and 0. Byte = 8 bits

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Memory, Bits, & Bytes' - genera


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
memory
Memory
  • Part of the computer where programs and data are stored.
  • Read and written (changed).
  • Bit
    • Binary digit
    • Basic unit of memory
    • 1 or 0
    • Why binary? Because we can most reliably (electronically) distinguish between 1 and 0.
  • Byte = 8 bits
    • Smallest unit of memory that can be read or written.
memory addresses
Memory addresses
  • Each individually addressable “cell” is an 8-bit byte containing 28 = 256 possible values (0..255).
  • The number of memory cells is independent of the cell size.
  • Most modern processors have at least a 32-bit address space.

232 = 4G bytes arranged 0..232-1

representing strings
Representing strings
  • Each byte will contain the ASCII value of a character.
representing strings1
Representing strings
  • So “hello” is the sequence of bytes:

104 101 108 108 111

  • But how do we determine the end of the string?

104 101 108 108 111 0

    • This method is also employed by C.
    • Other methods are possible.
integers in memory
Integers in memory
  • Each individually addressable “cell” is an 8-bit byte containing 28 = 256 possible values (0..255).
  • To allow for larger values, we group bytes together.
    • byte = 8 bits
    • word = 16 bits
    • double word = 32 bits (long word)
    • quadword = 64 bits
byte ordering
Byte ordering
  • Consider a word consisting of 2 bytes in memory with a value of 080116 at address 10.
  • It is a word (2 bytes) so it occupies memory location 10 and memory location 11.
  • It can be stored in memory as either:

M[10] M[11]

08 01 - big endian (Motorola)

01 08 - little endian (IA32, VAX)

- either (switchable): IA64, ultraSparc

endian ness
Endian-ness
  • Extends from 4 to 8 (and 16) byte integers too.
  • (Note: For integers larger than 2 bytes, other orderings are possible but they are not used.)
endian ness conversion
Endian-ness conversion
  • big endian: Motorola
  • little endian: IA32, VAX
  • bi-endian: IA64, ultraSparc
    • either/both supported
    • typically switchable at boot time
endian ness conversion1
Endian-ness conversion
  • What happens if one sends a message (that contains multi-byte integers) from one system to another across the internet, and they have different endian-ness?
    • We need a way to convert from one format to another (future topic; also see htonl Unix/Linux function).
ad