Storage Device components
-Storage medium
-Read/write mechanism
-Device controller
Storage medium
Data holding device
Read/write mechanism
Device used to read/write data values on a storage medium
Device controller
Interface device that connects the storage device to the system bus
Important characteristics of storage devices and technologies
-Speed
– Volatility
– Access Method
– Portability
– Cost & capacity
Speed
-the most important characteristic differentiating primary & secondary storage.
-Its essential because CPU must be continuously supplied with instructions & data to keep it busy.
Registers
-storage locations for Instructions & data in the CPU
-Their location enables zero wait states for access.
Wait state
a CPU cycle spent waiting for access to instruction/data
Access Time
=Storage device speed
-It is the time required to perform one complete read or write operation.
-It is the same for both reading & writing unless otherwise stated.
Data transfer rate
Comprising AT & the unit of data transfer to or from the storage
device
Types of fixed-size units per read/write operation
-Block
-Sector
Block
Amount of data transferred in one read/write operation
Sector
Amount of data transferred to/from an optical/magnetic disk in one read/write operation
Types of storage mediums/devices
-Non-volatile storage device
-Volatile storage device
Non-volatile storage device
Holds data without loss over long periods of time
Volatile storage device
Can’t reliably hold data for long periods of time
Access Methods categories
-Serial Access
-Random Access
-Parallel Access
Serial Access
Stores and retrieves data items in a linear/sequential order
Characteristics of serial access
-Data is written to a linear storage medium in a specific order & can be read back only in that same order.
– Access locations are organised serially (in a line)
– Access to location n requires accessing locations 1 through n-1.
– Old technology – avoid
Random Access/Direct Access
-No specific access order
- Any location on the storage medium can be accessed directly.
Parallel Access
= It simultaneously accesses multiple storage locations
