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

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

SRAM	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

Difference between RAM & ROM

RAM	ROM
Random Access Memory	Read Only memory
User can read & write into it	User can only read from it
For any type of processing, user must store program & data into RAM	Manufacturer stores instruction into ROM permanently
Temporary or volatile memory	Permanent or non-volatile memory

Cache Memory or High Speed Buffer

Cache Memory

• Cache memory is high-speed memory that holds the most recent data and instructions that have been loaded by the CPU.

• Cache is located directly on the CPU or between the CPU and RAM, making it faster than normal RAM.

• CPU-resident cache is called Level-1 (L1) cache. External cache is called Level-2 (L2) cache.

• The amount of cache memory has a tremendous impact on the computer's speed.

Secondary Memory or Secondary Storage Devices

Secondary Memory

Ø Nonvolatile

Ø Slow compared to primary memory

Ø Less costly & high capacity

Categorizing Storage Devices

• The hardware that writes data to or reads data from a storage medium is called a storage device. A floppy disk drive is a storage device.

• Storage devices hold data, even when the computer is turned off.

• The two primary storage technologies are magnetic and optical.

• Magnetic storage are:

-Diskettes (floppy disks)

-Hard disks

• Optical storage are:

-Compact Disk Read-Only Memory (CD-ROM)

-Digital Video Disk Read-Only Memory (DVD- ROM)

Comparison of primary & secondary memory

Characteristics	Primary	Secondary
Location with respect to the CPU	Directly accessible	Indirectly accessible
Cost	More expensive	Less expensive
Capacity	Lower than secondary memory	Several thousand times higher than primary
Means of storing information	Semiconductor chips	Magnetic and optical