Introduction to Storage
Computer data storage, often called storage or
memory, is a technology consisting of computer
components and recording media used to retain
digital data.
Primary Memory
Primary
storage often
referred to
simply as
memory, is the
only one
directly
accessible to
the CPU. The
CPU
continuously
reads
instructions
stored there
and executes
them as
Registers
• These are located inside the processor. Each register typically holds a word of data (often 32 or 64 bits
• Registers are the fastest of all forms of computer data storage.
Cache
• It is an intermediate stage between ultra-fast registers and much slower main memory.
• Most actively used information in the main memory is just duplicated in the cache memory, which is faster, but of much lesser capacity.
Main
• Main memory is directly or indirectly connected to the central processing unit via a memory bus
• It consists of RAM & ROM
Secondary Memory
Secondary
storage differs
from primary
storage in that it
is not directly
accessible by
the CPU. The
computer
usually uses its
input/ output
channels to
access
secondary
storage and
transfers the
desired data
using
intermediate
Magnetic
• It is usually used as secondary storage. The time taken to access a given byte of information stored on a hard disk is typically a few thousandths of a second, or milliseconds.
• It includes tape, Hard disk, floppy Disk etc.
Optical
• An optical disk is a high-capacity storage medium. An optical drive uses reflected light to read data.
• It includes CD-R, CD-RW, DVD, Blue ray etc.
Magnetic Storage
A magnetic disk's medium contains iron particles, which can be polarized—given a magnetic charge—in one of two directions(i.e. north or
Diskettes (floppy disks)
Hard disks
High-capacity floppy disks
Disk cartridges
Magnetic tape
Hard Disk Drive
Typically mounted inside the computer
Provides permanent storage and quick access
Stores information either on small disks called platters or in integrated memory chips
Read and write operations are managed by the controller
Data is transferred to and from the motherboard by the host adapter
Floppy Disk Drives Rapidly becoming obsolete
but still found in legacy applications
Most recent configuration accepted a removable 3 1/2" disk with a storage capacity of 1.44 MB
Traditionally assigned drive letters A: and B:
Power supplied through a 4-pin Mini power Connector (Molex)
Data transferred to motherboard through a 34-pin keyed ribbon cable
Optical Storage
Data is recorded to this type of media by stamping irregularities onto the surface of the disc, or "burned" into it using a laser, in a spiral pattern that runs from the inside to the outside of the disk.
Compact Disk
Digital versatile Disk
Blue Ray Disk
Compact Disk
Used for digital data storage
Formats include read-only (CD-ROM), write-once audio and data storage (CD-R), and rewritable media (CD-RW).
Storage capacity ranges from 650-900MB.
DVD
DVD discs can be single or double sided.
each DVD side may contain a second invisible "layer" to increase the disc's storage capacity.
4.7GB capacity(single-sided/single-layer)
8.5GB capacity (single-sided/double-layer)
9.4GB capacity (double-sided/single-layer)
17.1GB capacity (double-sided/double-layer)
Blue Ray Disk
High-density optical disc created with a blue laser
Used to store HD video and large amounts of data
25-50GB storage capacity single-layer
50-100GB storage capacity dual-layer
Flash Memory
Flash memory cards have high-capacity storage laminated inside a small piece of plastic
Flash memory cards do not need a drive with moving parts to operate
Flash Memory Talk
Example
s of Flash
Memory
Compact Flash (CF)
xD-Picture Card (xD)
Smart Media (SM) Card
Secure Digital (SD) card
Multi Media Cards (MMC)
Tertiary Memory
Tertiary storage or tertiary memory, provides a third level of storage. Typically it involves a robotic mechanism which will mount and dismount removable mass storage media into a storage device according to the system's demands; this data is often copied to secondary storage before use.
Examples are Tape libraries& optical juke boxes
Memory Addressing
Memory is a collection of cells, each with a unique physical/memory address
Each cell can hold one byte or 8 bits
The cell contents can change, but the cell address or reference to the cell is always the same.
Storage Memory Terms
= 8 bits
≈ 1 Thousand Bytes
≈ 1 Million Bytes
≈ 1 Billion Bytes
≈ 1 Trillion Bytes
≈ 1 quadrillion Bytes
≈ 1 quintillion Bytes
1 Byte
1 Kilobyte (KB)
1 Megabytes (MB)
1 Gigabytes (GB)
1 Terabytes (TB)
1 Petabyte (PB)
1 Exabyte (EB)