1 / 10

Memory, Bits, & Bytes

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

genera
Download Presentation

Memory, Bits, & Bytes

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. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Memory, Bits, & Bytes

  2. 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.

  3. 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

  4. Representing strings • Each byte will contain the ASCII value of a character.

  5. 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.

  6. 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

  7. 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

  8. 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.)

  9. Endian-ness conversion • big endian: Motorola • little endian: IA32, VAX • bi-endian: IA64, ultraSparc • either/both supported • typically switchable at boot time

  10. 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).

More Related