1. Secondary Storage Devices
Permanent Storage!!
Secondary Storage Devices

2. Magnetic and Optical

3. Storage Device
A storage device is a hardware component used to store data, programs, and instructions. Devices may be magnetic or optical.
Magnetic: floppy and hard disks/hard drives. Magnetic media uses magnetic patterns to store data on the disk’s surface.

4. Floppy Drive
The floppy disk is used to store small amounts of data. Up to 1.44 mb.
The floppy drive stores binary data ( a series of 0’s and 1’s) as a magnetic pattern on the disk’s surface.
The data are stored on tracks and sectors. Tracks are circular bands or concentric circles.

6. Floppy Disk
Data are stored on both sides of the disk. The floppy disk has 80 tracks and 18 sectors on each track. A sector stores about 512 bytes of data.
A track is a very narrow recording band that forms a full circle on the surface of the disk.
The disk storage locations consists of pie-shaped sections, which break the track into small arcs called sectors.

7. Hard Disks

8. Hard disks/drives
Hard drives usually consist of several disks or platters on a single spindle. Each platter has a number of tracks. A cylinder is the location of a single track though all the platters.

9. Hard drive
Cylinder

10. Hard Disks
Data is stored on both sides of the platters and each platter has its own read/write head.
This enables the read/write heads operate simultaneously, which means that data can be transferred more quickly, than by using a single, larger disk.
The hard disk spins continuously at a very fast rate, about 5400 to 7200 rpm ( revolutions per minute) and has an access time of about 8ms.

11. Hard Disk Vs Floppy disk
Access Time:
A hard drives access time is significantly faster than that of a floppy disk for two reasons.
A hard drive spins a lot faster than a floppy
A hard disk spins constantly while a floppy only starts to spins when it receives a read or write command

12. Hard Disk
The hard disk, floppy and optical media all use direct access.
If the read/write head touches the surface of a platter, it causes a “head crash”. This may be caused by particles of dust or shock to the system. A head crash can damage the hard drive and cause loss of data.

13. Hard Drive

14. Hard Drive
Hard drives are available in many sizes. A typical hard drive can range from 40 GB to 500 Gb and even 1 or 2 TB.

15. Hard Drive
Many read write heads

16. Hard Drive
The Read/Write head

17. Hard Drive
HOW HARD DRIVES WORK
DETAILED INFORMATION ON THE HARD DRIVE

18. Types of Hard Disk Fixed Head and Moving Head Hard Disks: FIXED HEAD:
There is a read-write head for every single track, on every platter.
MOVING HEAD:
There is only one read-write head for each platter. Therefore the head has to move from track to track.

19. Types of Hard Disks TERMS TO LEARN Rotational Delay: Seek Time:
The time it takes for Disc to spin so that the beginning of the data being read is directly below the read/write head.
The time required for a disk reach a position where the read/write head can be positioned over the desired data.
Seek Time:
The amount of time that a read/write head takes to move to a specific track on a disk.
Access Time:
Seek Time + Rotational delay: The time taken to retrieve data from the disk.

20. Types of Hard Disks
A fixed – head hard drive is faster than a moving – head hard drive because the access time is faster. WHY?
Therefore they are usually more expensive.

21. Hard Disk Controller
This is a special purpose chip and associated electronic circuits that control the transfer of data from the hard disk to the rest of the computer. Some refer to the disk controller as an interface.
Research the following interfaces:
SCSI (pronounced “scuzzy”)
EIDE

22. External hard drives

23. Magnetic Tape

24. Magnetic Tape Looks Similar to magnetic tape
Mainly used for making backup (security) copies of hard disks because it can store large amounts of data at low cost.
Storage capacity of about 120 GB.
Much slower access rates than other magnetic media because it uses sequential access.
A tape drive is used to access the data from the magnetic tape

25. Optical Storage Devices

26. Optical Discs CD’s: COMPACT DISCS:
Also called an optical disc, is a flat, round, portable, metal storage medium that usually is 4.75 inches in diameter and less than 1/20 of an inch thick.
The CD stores data by using microscopic pits ( indentations) and lands (flat areas) that are in the middle layer of the disc. Data is read from the disc using a laser. Pits absorb the light (0’s) and lands reflect the light (1’s).

27. Optical Discs
A compact disc typically stores data in a single track that spirals from the centre of the disc to the edge of the disc.

28. Optical Discs
As with the hard disc, this single track is divided in evenly sized sectors in which items are stored.

29. Types of Optical Discs CD-ROM: CR – READ ONLY MEMORY
You can only read from it. ( e.g. original music CD)
CD-R: CR - Recordable
You can put stuff on but you can’t take stuff off. Multisession. You add some data now and more data later until the disc is full.
CD-RW: CD – Rewritable
You can write and erase.
Storage capacity for most CD’s: 700mb

30. Types of Optical Discs DVD: Digital Video Disk/ Digital Versatile Disk
Much higher density then CD therefore a more powerful laser is needed.
Storage Capacity: 4-8 gb
DVD-ROM
DVD-R
DVD-RW

31. FLASH DRIVE & FLASH MEMORY
Flash Memory utilizes “SINGLE STATE STORAGE”, which mean there are no moving part. ( no disc spinning, no read write head)…..COOOL!!!!
Bits are stored as electrons with in gates.
How data is stored on flash memory