Secondary Storage

1. Secondary Storage CIS 105

2. List the benefits of secondary storage. Identify and describe storage media that are available for personal computers. Describe how data is stored on a disk. Lists the items that effect a hard drive’s access time. Topics

3. Information Processing Cycle InputRaw Data Process (Application) OutputInformation Storage Output from one process can serve as input to another process.

4. Secondary Storage • Secondary storage is used to store programs and data that are not currently being used. • Examples: • Hard drive, USB Flash Drives , CD, DVD • When programs and data are needed, they must be retrieved from the storage device and loaded into RAM (primary storage). • The CPU only executes commands and manipulates data loaded in RAM.

5. Memory (RAM) vs. Storage(Volatile) (Non-volatile) Temporarily holds program instructions to be executed and data that is currently being manipulated. Holds data, instructions, and information that can be retrieved and loaded into RAM when needed.

6. Benefits of Secondary Storage • Benefits • Space • Reliability • Convenience • Economy • Programs and data can be saved and retrieved when needed. • Referred to as Reading and Writing.

7. Multi-platter Drives Hard Drives

8. Hard Disk Characteristics • Read and Write heads are used to store and retrieve data. • Read and Write heads do NOT touch the platters, if they do, it is called a Head Crash. • Data is stored magnetically. • Access arms are used to position the heads. • Multi-Platter - both sides of platter are recordable. • Very large capacity. • Removable and External hard drives are now available,and are great for backups.

9. Format Commands • Low Level Format – software provided by vendor. • High Level Format – performed by operating system. • Formatting is the process of preparing a storage device for reading or writing. • Formatting erases all data on. • Partitions can be created during formatting, and a partition is a logical division of a hard disk created so that you can have different operating systems on the same hard disk or to create the appearance of having separate hard drives for file management, multiple users, or other purposes. • Format defines Tracks, Sectors, Cylinders, and File Allocation Table (FAT) – this items are defined in the next few slides.

10. Tracks and Sectors Formatting organizes the disk into storage locations called tracks( a band that forms a circle on the disk). Formatting breaks the tracks into sectors which are small pie-shaped areas. Data processed one or more sectors at a time called clusters. In a multi-platter hard disk, the same track on multiple platters together form a cylinder (next slide). Tracks Sectors (Cluster: 1-8 sectors)

11. Cylinders • In a multi-platter hard disk, the same track on multiple platters together form a cylinder.

12. MZR • With normal sectors, there is a lot of wasted space on the sectors located on the outer tracks. • Multiple Zone Recording (MZR) – data is recorded at the same density on all tracks so that outer tracks have more data.

13. File Allocation Table (FAT) • FAT – list of clusters and used to keep track of where files are on the disk. • FAT includes Filename, File size, and the cluster number of where a file begins and additional directory info • When a file is deleted, the data on the disk is still there, only the entry in the FAT is marked as deleted so another file can eventually be saved in it’s location. • That is why data can still be recovered after you think it has been deleted. • NTFS – Windows New Technology File System is more secured then FAT and uses MFT (Master File Table) to track where files are stored. • FAT and MFT are stored on the actual storage device.

14. Access Time • Access Time -the time required to locate data on the storage device – 3 things affect access time. • Seek Time – the time it takes the access arm with the read/write heads to get into position over the track. • Head Switching – the activation of a particular read/write head. • Rotational Delay (latency) – the time it takes for the sector containing the data to rotate under the read/write head.

15. Data Transfer Rate • Data Transfer Rate – the time it takes to transfer the data to and from the disk to RAM. • While the computer is running, the platters spin at a constant high speed, 5400-15000 revolutions per minute (rpm).

16. Hard Disk Controller • Hard disk controller transfers data between the hard disk and the system bus. • The controller may be part of the hard disk, motherboard, or a separate expansion card. • Common Interfaces: • SATA – Serial Advanced Technology Attachment Some external drives can use this interface (eSATA) transfer rate: 1.5 or 3.0 gigabits per second (Gbit/s) • EIDE – Enhanced Integrated Drive Electronics (parallel)Also know as ATA and PATAtransfer rate of last version ATA-7: 133 Mbits • USB 2.0 transfer rate: 480 Mbits per second (use eSATA)

17. Fragmented Disk • Fragmented disk occurs when files are stored in non-contiguous clusters • How does fragmentation affect access time? • http://www.diskeeper.com/ • Perfect Disk – www.raxco.com

18. Windows Disk Defragmenter

19. RAID (Redundant Array of Independent Disks) There are about 9 levels Level 1 - Data is duplicated – auto backup and fault tolerant – disk mirroring with no striping (RAID LEVEL 0) Can be Combined Level 0 - File saved across different drives called striping.

20. Optical Storage Technology • Compact Discs (CD) • CD-ROM – Read Only Memory • CD-R – Recordable – Write Once • CD-RW – ReWritable • Digital Versatile Discs (DVD) • DVD – Read Only • DVD-R, DVR+R – Recordable – Write Once • DVD-RAM, DVD-RW, DVD-+RW – ReWritable

21. Compact Disc Drives • CD-ROM - drive can only read data from CDs • CD-ROM stores up to 650 MB per disk • CD-R - drive can write to disk once • Disk can be read by CD-ROM or CD-R drive • CD-RW - drive can erase and record data multiple times on RW media • Some compatibility problems trying to read CD-RW disks on CD-ROM drives

22. Digital Versatile Disk (DVD) • Short wavelength laser can read densely packed spots • DVD drive can read CD-ROMs • Capacity from 4.7GB (Single Layer-Single side) up to 27GB (Dual Layer-Double Side) • Data store tighter on higher capacity discs. • Allows for full-length movies • High-Density DVD (HD-DVD) 15 - 60GB • Blu-ray discs – 25 – 100GB (2007 became industry standard)

23. DVD-Dual Layer (pcworld 4/2005) • Two layers, one disc: This side view shows the two dye-recording layers of a double-layer DVD. When the laser writes to the disc, it directs its beam to either layer one or layer two.

24. Magnetic Tape Storage • Plastic tape with a magnetic coating. • Primarily used in large organizations. • There are small tape drives for small businesses and home use, but not too common. • Need a tape drive • Erase head • Read/Write head • Used for backups. • Sequential access

25. Flash Memory Cards • A flash memory card is a removable storage device. • Consists of circuits with NO moving parts. • Used by PDAs, phones, digital cameras, some MP3 players. • Includes USB Flash Drives.

26. Backup System • Need to backup data on storage devices. • Copies should be saved onsite and offsite. • Why? • Hard drives may fail (head crash) • Fire • Natural disasters • Thief • Vandalism • Government requirements • To save your job

27. List the benefits of secondary storage. Identify and describe storage media that are available for personal computers. Describe how data is stored on a disk. Lists the items that effect a hard drive’s access time. Summary