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Thursday, December 25, 2008

Dot Matrix Print Head

  • Impact printer
  • Print head strikes inked ribbon
  • Line printers
  • Band printers
  • Speed measured in characters per second

Ink-jet printers

  • Non-impact printer
  • Inexpensive home printer
  • Color output common using CMYK
  • Cyan, magenta, yellow, black
  • Sprays ink onto paper
  • Speed measured in pages per minute
  • Quality expressed as dots per

Laser printer

Non-impact printer

Produces high quality documents

Color or black and white

Print process

Laser draws text on page

Toner sticks to text

Toner melted to page

Speed measured in pages per minute

Quality expressed as dots per inch

Definition of memory and its classification

Memory Hierarchies

Definition of memory and its


Ø Memory

When you launch a program, it is loaded into and run from memory

Ø Classification of Memory

Ø Internal Processor Memory

Ø Main Memory:

Example: RAM, ROM.

Ø Secondary Memory:

Example: CD, Floppy etc.

Memory Capacity

ü Bit

ü Byte: 1 byte= 8 bits

ü Kilobyte (K or KB): 1KB=1024 bytes

ü Megabyte (M or MB): 1MB=1048579 bytes

ü Gigabyte (G or GB): 1GB=1048876 byte

ü Terabyte

Memory Hierarchies

General Properties of Memory Devices

Access Time: The average time required to read a fixed amount of information from the memory

Cycle time: The minimum time between two consecutive memory access operations is called the cycle time.

Data Transfer rate: The maximum amount of information that can be transferred to or from the memory every second is called the data transfer rate.

Main memory or Primary memory

Main memory or Primary memory

Ø Read only Memory

Ø Random Access Memory

Ø Cache Memory

Read only Memory (ROM)

    • Read Only Memory.
    • Used for storing programs & data permanently.
    • User may read data from ROM but may not write on ROM.
    • Permanent or Nonvolatile memory

Random Access Memory (RAM)

Ø Temporary storage that can be read from or written into by the user.

Ø Used primarily to store user programs and data.

Ø Temporary or Volatile memory.

Ø Determines a computer’s speed and power

Ø 2 types of RAM:

Static RAM

Dynamic RAM

Differences between SRAM and DRAM



High speed RAM

Relatively slower

SRAM is costly

Less costly

Does not require refreshing

Requires refreshing periodically

Generally used for cache

Used for main memory