Lecture 4: Secondary Storage

I. Secondary Storage (Hard Drives) Secondary Storage Secondary Storage: holds data and programs for future use by providing permanent nonvolatile (non – changeable) storage Processing data can be held in secondary storage Secondary storage is also known as external storage or auxiliary storage. Secondary Storage Secondary Storage has several advantages that allow users to store an unlimited amount of data and programs  convenience – locate and retrieve stored data and programs quickly and easily  inexpensive  reliable  large capacity

II. Data: Sizes from smallest to largest BIT a BIT is the smallest unit of data a computer can store a unique combination of bits represents a character BYTE a BYTE = 8 bits KILOBYTE a KILOBYTE (KB) = 1024 bytes (typical high speed download rate) MEGABYTE a MEGABYTE (MB) = 1,000 kilobytes GIGABYTE a GIGABYTE (GB) = 1,000 megabytes TERABYTE a TERABYTE (TB) = 1,000 gigabytes

III. Hard Drives / Magnetic Disks common use of secondary storage - backup hard drive / hard disk – made of rigid metal and flexible plastics with an easily magnetized substance Hard Drive – made out of aluminum, huge storage capacity and very quick data access Data – is magnetically recorded onto “tracks” random access An address is assigned to every track on a hard drive This “system of addresses” is known as random access – (also known as direct access) Hard disks spin constantly (i.e rotations per minute) Data is written and read by a “read/write head” that floats on a pocket of air Disk access time Disk access time – the time it takes between entering a request for data (opening a file) and actually receiving that data – measured in milliseconds

IV. CD / DVD Technology OPTICALLY CD-Rom and DVD-Rom drives read and write data using a laser. Both CD and DVD drives read lasers OPTICALLY rather than MAGNETICALLY. Currently, there are two types of lasers: 1) Red lasers – older technology 2) Blue lasers – newer technology that allows drives to read and write larger amounts of data at faster speeds (is a larger laser and is used in high definition)

CD’s and DVD’s (continued) RED LASER MEDIUMS Regular CD’s (CD-R or CD-RW): hold 700 MB of data or 80 minutes of audio Regular DVD’s (DVD+ / DVD- / DVD-RW): single layer DVD’s hold 4.7 GB dual layer DVD’s hold 8.5 GB BLUE LASER MEDIUMS HD-DVD (High Definition DVD): HD-DVD’s utilize 1080p single layer DVD’s hold 15 GB dual layer DVD’s hold 30 GB Blu-Ray (High Definition DVD): Blu-Ray also supports 1080p single layer DVD’s hold 25 GB dual layer DVD’s hold 50 GB

HD – DVD vs Blu-Ray HD – DVD Blu-Ray