Storage Devices

Introduction to storage devices

Storage devices are responsible for storing data, storing the data even when the computer has been switched off.
Storage devices are usually slow and include and include a variety of devices such as hard drives, CD -ROM Drives, DVD drives, and floppy drives .

Key Topics

Storage Devices
Hard Drive Speed
Hard Drive Preparation
Defragmentation
SCSI Devices

IDE Devices
EIDE Devices
CDROM Storage
CD -RW
DVD Storage
Floppy Drive

Introduction to Storage Devices

Storage devices are used for storing and backing up data and retrieving previously stored data.
They are usually not as fast as solid-state devices such as memory and CPU because they have moving parts.
There are a number of technologies in the market for storing data including; Hard drives, Floppy Drives, CD -ROM ’s, DVD , tape drives etc.
These technologies have varying speeds, sizes, prices and storage mediums depending on the technology at hand.
Non conventional storage devices designed to replace the floppy drive as temporary storage
The main storage device used on computers is the hard drive which had enormous increases in its capacity in the last fives years.
The system hard drive has not increase in it physical size that reflects the advances in hard drive technology.
HD sizes range from several MB to several hundred GB .

Internal and external storage ports

These storage devices also use different interfaces to communicate to the system including IDE , SCSI , Parallel, USB , 1394 etc.
The two main internal interfaces to these storage devices are IDE and SCSI

The standard hard drive has a design similar to the gramophone. The hard drive contains several magnetically sensitive plates that are vertically attached above each other. Each plate is divided in sector cutting the plate in to quadrants. The plate’s surfaces have traces defined on them from the outer edge to the inner edge called cylinders . Within every drive there exists several magnetic heads situated on an arm that can write and delete the data on each plate.

Hard Drive Speed

Drive speed is a combination of Access Time (how quickly data is found) and Data Transfer Rate (speed of reading and transferring the data)
Seek time = time taken for head to position itself over required track
Drives contains platters which are magnetically sensitive and read /write heads which generate magnetic pulses for 1’s and 0’s written on both sides of the platters

Hard Drives LBA

LBA (Large Block Access) is used by the BIOS chip on the Hard drive to communicate and configure drive size settings in the system BIOS on large drives bigger then 528MB

Zone Bit Recording

Zone Bit Recording (ZBR ) is a new technology for increasing the number of sectors on the outer edge of the platters to increase the capacity of the drive.
To cope with sector size changes with increase in radius size on a plate , the disk is set spinning at different speed, depending on where the data is on the disk.
ZBR technology is used in CD ROM drives

HD Preparation

There are three stages in drive preparations after the drive has been recognized by the system BIOS , Low-level format (LLF ), Partitioning , High-level format (HLF ).

Low Level Format

Low Level Format (LLF ) is a process performed by the manufacturer in which the sector ID is defined. These sector ID’s are used as landmarks for finding the data by the operating system .
LLF is an operation that can be performed by the BIOS although not recommended on modern drives.
Drive selection screen shot and Low level format screen shot from the BIOS

Partitioning

Partitioning is a process of dividing a drive in to separate sections.
It is ideal for dual booting environments and different filing systems, such as FAT16 , FAT32 , and NTFS .
Partitioning is very useful for inefficient filing systems such as FAT16 .
A program called FDISK.EXE in DOS and windows 95/98 performs partitioning.
Partitioning your hard drive with Fdisk.exe available in DOS windows 95/98.
High Level Format (HLF ) is always performed by the operating system (OS) of interest.
HLF write on the disk the filing structure used by that particular OS which allow files to be written and located on the disk, also creates boot records, and a directory system.

Hard Drive Compression

Compression is the process of reducing data disk consumption by taking the data through a special mathematical formula usually performed on FAT 16 filing system.

Defragmentation

Fragmentation happens when related files are dispersed throughout the disk due to lack of space in one region on the disk.
Fragmentation slows down your disk and increases access time
Defragmentation is performed by a program called DEFRAG.EXE
Defrag organizes the related files in contiguous order.

Introduction to SCSI

SCSI is usually pronounced as Scazzy.
SCSI peripherals are intelligent and have their own bus that does not require the CPU
SCSI is a universal standard , which means that SCSI peripherals can be, used with any hardware including PC’s, Mac’s, Sun systems, etc.
Most peripherals are produced in SCSI design including Hard drives, CD -ROM drives, Tape drives, Raid systems, Scanners , printers etc.
SCSI devices generally cost more and are more reliable and expensive than the non-SCSI alternative.

SCSI Rules

The SCSI bus can link up to 8 devices including the SCSI adaptor.
Each SCSI peripheral must have a unique ID number from 0 to 7 determined either by Dipswitches or jumpers on each device.

SCSI ID’s

SCSI Rules

SCSI ID number 7 is assigned to the SCSI adaptor card.
SCSI ID number 0 is assigned to the first SCSI hard drive
All SCSI devices are daisy chained to each other by the SCSI cable .
The adaptor may be places at the beginning of the chain if we only have either internal devices (HDs, CD -ROMs, etc) or external devices (Scanners , Printers, etc).
The adaptor may be placed in the middle of the chain if we have both internal and external devices connected to the chain.
The chain must be terminated at both ends using a terminator .

SCSI Standards

SCSI 1 or SCSI A is the original version of SCSI which had initial problems due to inconsistencies and incompatibilities between SCSI peripheral manufacturers and cards known as command set.
The SCSI standard uses a 50 pin centronics D shell connector to connect SCSI devices to the SCSI adaptor.
SCSI 2 resolved all previous inconsistencies, and added new features such as dual channel for multiple instructions , Parity checking, error detection, error correction, synchronous data transfer .
Ultra SCSI achieves fast speeds of 20MB/s on 8bit bus and 40MB/s on 16bit bus. It allows burst transfer and allows up to 16 devices to be connected (0-15). It also has plug and play features called SCSI configuration automatically (SCAM).

IDE Devices

IDE = Integrated Device Electronics
IDE is also known as ATA, EIDE , ATA-2, Fast ATA
Most common interface for HD and CD ’s
IDE controller takes up IRQ 14
Requires a single 40 pin data and control cable from HD to I/O controller
Each cable can accommodate two IDE devices
Maximum IDE HD space is 528MB
If two IDE drives are used, master and slave must be identified on the appropriate drive using the jumper settings

BIOS Setting of IDE

Provided the drives are connected correctly, the system BIOS will detect the drives on modern systems.
If using an older 486 systems, drives must be identified as type 47, and the values of its cylinders , heads, and sectors must be recorded in the system CMOS
The BIOS has auto detection option for hard drives.

EIDE Devices

EIDE = Extended Integrated Device Electronics
Can control up to 4 separate IDE Devices on two controllers built on system board
EIDE controllers take up IRQ 14 and IRQ 15
HD size is only limited by BIOS limitations and can be changed on Pentium systems by upgrading the BIOS on the flash Ram.

CD ROM Drive

CD -ROM drives can only read data.
Now days it is used not only used to store programs and applications , but also personal data.
Can store between 650MB to 700MB of data on a CD .
Can connect internally to motherboard by several different interfaces a) using its own controller card or a proprietary sound card b) can share the IDE controller with the HD ’s, and finally c) can share a SCSI controller with a SCSI CD -ROM drive.
Master and slave jumpers must be set accordingly on IDE CD -ROM drives.
SCSI CD -ROM drives must have there ID jumpers set correctly

Recording on CD ’s

Recording on CD ’s are now becoming a very popular technology for storing large quantities of personal data, music and multimedia .
CD -R is the first of these technologies which only records data only once in any one section of the CD.
Speeds for a CD -R drive is write = 4X, Read =20X.
CD -R ’s laser head must have no interruptions in the data flow when writing data on to CD.

Re-recording on CD ’s

CR-RW is re-writ able technology, which uses a special more expensive re-writ able CD to record the information
CD -RW recorded CD’s are not readable in all CD-ROM drives.
Can be connected to the system board the same way as the CD -ROM drive.
There are also external CD -recorders, which can connect to the system, parallel port , USB port, and 1394 port.

DVD Technology

Can store up to 17GB of data.
DVD readers are readily available at a reasonable price.
DVD technology can be used for storing movies, sound, and data, in a universal disk format (UDF )
DVD Writers are now available at very expensive prices storing up to 4.7GB on a single side layer.
DVD are both double sided and double layered giving them a maximum capacity of 17GB’s.

Drive comparison

Floppy Drive

Floppy disks are used mainly for transporting small amounts of data.
The floppy drive ribbon cable has 34 pins and can connect two drives to the floppy controller.
The A: drive should be attached to the connector after the twist .
If you need to attach a B: drive, it should be attached to the connector before the twist .
The red wire on the ribbon indicates pin 1.
Old standard was 5¼ inch, which could hold 360KB of data on its double density disks and 1.2MB of data on its high density Disks.
The 5¼-inch disks are flexible and can be bent.
The 3½-inch is used on all systems today, it can hold 1.44MB of data on its high-density disks, and the older double density disks could hold 720KB of data.
The 3½-inch disks have a rigid cover and cannot be bent.

Floppy disk characteristics

DD = Double Density HD = High Density

EHD = Extra High Density

What is a Viruses

A virus is a program designed to have two main functions in life: destruction of computer data/hardware and reproduction of the virus itself on to other devices
The main medium for virus transfer is either a diskette or the Internet , although it can be transferred by other mediums.
When a computer user places a diskette in to the computer previously infected by a virus , the virus will automatically try and transfer itself on to the disk.
This Virus will infect other computers when the diskette is used on them unless an anti virus program has previously been installed on the non-infected computers.
You can lock the floppy drive from being overwritten by closing the hole at the bottom of the disk. Using this lock we can protect our disk from viruses.

Internet Viruses

Internet viruses predominantly infect computers either by through e-mail, or when downloading sharewares.
E-mail viruses infect your system when you open a disguised e-mail attachment and then expand their circle to other machines using your e-mail contacts list and send the same infected e-mail to all the people you know.

Questions

1) What is the storage capacity of a CDROM drive?

a) 650MB

b) 1GB

c) 2GB

d) 200MB

e) 1.44MB

2) What is the storage capacity of a ZIP drive?

a) 650MB

b) 1GB

c) 2GB

d) 200MB

e) 1.44MB

3)What is the storage capacity of a floppy drive ?

a) 650MB

b) 1GB

c) 2GB

d) 200MB

e) 1.44MB

4) How many pins does a standard IDE controller have?

a) 24 pins

b) 36 pins

c) 40 pins

d) 34 pins

e) 50 pins

5) How many pins does a standard floppy controller have?

a) 24 pins

b) 36 pins

c) 40 pins

d) 34 pins

e) 50 pins

6) How many pins does a standard SCSI controller have?

a) 24 pins

b) 36 pins

c) 40 pins

d) 34 pins

e) 50 pins

7) What factors define Hard drive speed? (choose all that apply)

a) Access time

b) Data time

c) Data transfer rate

d) Flow time

8)What factor is used by the BIOS to define drives bigger then 528MB?

a) LBA

b) LLF

c) DDF

d) HLF

9) What are the features of Low level Format LLF ? (choose all that apply)

a) Defines sector ID's

b) Performed by the BIOS

c) Performed by the OS

d) Performed by the drive manufacturer

e) No required for IBM compatible PC drives

10) What is the function of Fdisk.exe?

a) Defragments your hard disk

b) Partitions your hard disk

c) Compresses the drive

d) Formats the drive

e) Generates volumes

11) Which of the following are features of SCSI ? (Choose all that apply)

a) All devices must have unique ID number

b) SCSI ID 0 belongs to the SCSI controller

c) The SCSI devices are daisy chained to each other

d) The SCSI devices are terminated at both ends

e) SCSI ID 7 belongs to the first hard drive

12) What IRQ is used by the secondary IDE controller?

a) 2

b) 5

c) 12

d) 14

e) 15

13) How many IDE devices does EIDE support?

a) 2

b) 1

c) 3

d) 4

e) 6

14) Which drive exist after the twist on the floppy cable ?

a) A

b) B

c) C

d) D

e) E

15) What defines the maximum size of EIDE drives used on a computer?

a) The Hard drive

b) The CMOS

c) The BIOS

d) The cable

16) What drive letter will be picked up by the primary partition of the second and final drive?

a) C:

b) D:

c) E:

d) F:

e) A:

Answers

A
D
E
C
D
E
A,C
A
A,B,D
B
A,C,D
E
D
A
C
B