Chapter goals

Data transfer rate

• Expressed in terms of bytes/second
• Access time combined with data transfer unit
• Data transfer rate describes how much data can be transferred between devices over a period of time

Volatility

• Volatile – storage device is volatile if it cannot reliable hold data for long periods of time
• Non–volatile – storage device is non-volatile if it can reliably store data for long periods of time
• Computer systems need a combination of volatile and non-volatile storage devices

Access method

• Physical structure of storage device’s read/write mechanism determines the way(s) data can be accessed
• Serial access
• Random access
• Parallel access

Serial access

• Stores and retrieves data items in a linear or sequential order
• Slowest access method
• Tape typically used for backup purposes

Random access

• Also called a direct access device
• Can directly access data stored on the device
• All primary storage and disk storage devices are direct access
• Parallel access – with multiple read/write heads, can simultaneously access more than one storage location