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CHAPTER 9. Basic Disk Drives. Chapter Overview. Floppy Disk Drives Hard Disk Drives. The Basics of Floppy Disk Drives. In 1972, IBM developed the First floppy disk drives for its system 370 machines. these drives used 8-inch floppy disk. - PowerPoint PPT Presentation
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CHAPTER 9
Basic Disk Drives
Chapter Overview
Floppy Disk Drives Hard Disk Drives
The Basics of Floppy Disk Drives In 1972, IBM developed the First floppy disk drives for its system 370 machines. these drives used 8-inch floppy disk.
When IBM introduced the personal computer (PS) in 1981, it came standard with a 5.25-inch floppy.
Today’s 3.5-inch floppy disk are made of flexible plastic and coated with a magnetic material.
Major differences between the 5.25-inch and 3.5-inch:
Physical size.
5.25-inch has a slot connector.
3.5-inch has a pin connector.
Different power plug and voltages.
Keeping a Floppy Disk Drive Running Schedule monthly cleanings. Check the floppy disk first for data errors or write protection. Check complementary metal-oxide semiconductor (CMOS) settings. Check or change the floppy disk drive cable. Change the floppy disk drive controller. Replace the floppy disk drive as needed.
Errors Caused by the Floppy Disk First , make sure the disk is not write protected. The hole on the right top corner should be closed.
Try another disk.
Try a new ( formatted) disk.
Try someone else’s disk , one that is known to work on another computer.
Try going to MS-DOS and reading a directory using the DIR command.
POST will return “ FDD controller failure “ or “ drive not ready” errors in the event of a loose data cable or power plug.
I/O card with floppy disk controller
Hard Disk Drives
Hard disk drives are mass storage devices.
The First hard disk drives were small in capacity , physically and expensive.
In 1981, IBM introduced the XT computer with a 10-MB hard drive.
Today, a new hard disk drive can fit in your pocket and hold over 40 GB of data.
Physical Characteristics The First form of PC mass storage was the magnetic tape drive. The typical cassette drive cartridge was easily damaged. Gaining access to the data was slow due to the way data is organized
on tape. Tapes were hundreds of feet long, and users often had to run the
entire length of the tape to find the data they were seeking. The original concept behind the hard disk drive was to provide a
storage medium that hold large amounts of data and allowed fast random access to that data.
The First IBM hard disk drives were code-named “ Winchester”. The PC-XT was the First personal computer to include a hard disk. Hard disk drives are composed of several platters , matched to a
collection of R/W heads and an actuator. The distance between the heads and the disk surface is less than the
thickness of a fingerprint.
Storing Data Data is stored using binary code. 1s and 0s are stored in computer’s memory as electrical
impulses. On magnetic media , the 1s and 0s can be stored as either
magnetic or nonmagnetic areas on the drive surface. The 0s and 1s of the binary code are stored in terms of flux
reversals. Flux reversals are actually the transitions between
magnetized and nonmagnetized positions on the hard drive surface.
FM technology is based on timing. To differentiate a 1 from a 0, it measures the time the drive head spends
in a magnetized state. The name "frequency modulation" comes from the fact that the num of
reversals is doubled for ones compared to that for zeros. This can be seen in the patterns that are created if you look at the encoding pattern of a stream of ones or zeros. A byte of zeroes would be encoded as "RNRNRNRNRNRNRNRN", while a byte of all ones would be "RRRRRRRRRRRRRRRR". As you can see, the ones have double the frequency of reversals compared to the zeros; hence frequency modulation (meaning, changing frequency based on data value).
FM encoding write waveform for the byte "10001111".Each bit cell is depicted as a blue rectangle with a pink line representingthe position where a reversal is placed, if necessary, in the middle of the cell.
Frequency Modulation ( FM)
Storing Data cont
MFM: uses the previous data bit to indicate whether the current bit is a 1 or a 0.
Reduce the timing by considering not just the current bit but also the one before it .
IN RLL : It considers groups of several bits instead of encoding one bit at a time
Physical Characteristics
Actuator Arms
Hold read/write (R/W) heads in place Must deliver speed and accuracy Use one of the following technologies:
The stepper motor (older) had many disadvantages.
The voice coil motor (newer) uses the head for mapping.
Might be damaged by head-to-disk interference (HDI), or head crash
Stepper Motor
hard disk drives used a stepper motor to control the movement of the heads over the surface of the platters.
A stepper motor actuator. The motor moves in steps, which you can feel ifyou move the motor shaft by hand.
voice coil motor The actuator in a modern hard disk
uses a device called a voice coil to move the head arms in and out over the surface of the platters, and a closed-loop feedback system called a servo system to dynamically position the heads directly over the data tracks.
When current is fed to the coil, an electromagnetic field is generated that causes the heads to move in one direction
Check pages 192,193 :the disadvantages of each type
Head-to-disk interface(HDI) or head crash : these terms describe the contact that sometimes occurs between the surface of the disk and the R/W head.
Geometry
Watch video
Geometry : the geometry of a hard drive is the organization of data on these platters.
Geometry determines how and where data is stored on the surface of each platter.
Heads: the number of heads is relative to the total number of sides of all the platters used to store data.
Cylinder: data is stored in circular paths on the surface of each platter. Each path is called a track,. There are hundreds of tracks on the surface of each platter. A set of tracks through each platter is called a cylinder.
Sector per track: A hard disk drive is cut into tens of thousands of small arcs, each arc is called a sector and holds 512 bytes of data.
CHS values: cylinder, heads, and sectors per track are known as CHS values. The capacity of any hard disk drive can be determined from these three values.
The maximum CHS values are:
1024 cylinders.
16 heads
63 sectors per track
512 bytes per sector
Hard Disk Drive Types
ST-506 Enhanced Small Device Interface (ESDI) Integrated Device Electronics/Enhanced
Integrated Drive Electronics (IDE/EIDE) Small Computer System Interface (SCSI)
The first hard disk drive for personal computers, introduced in 1979 by Seagate. It was used in drives of 40MB and less and transferred data at 625 Kbytes/sec, using the MFM encoding method.
ST-506 uses a 34-connector control cable and 20-connector data cable.
ST506
Enhanced Small Device Interface (ESDI)
The first attempt at improving the original ST-506/ST-412 hard disk interface was the Enhanced Small Device Interface or ESDI. ESDI was developed in the mid-1980s by Maxtor.
ESDI improved on ST-506/ST-412 in several ways. It moved some drive controller functions to the hard disk from the controller card, eliminating some of the reliability problems associated with its predecessor.
IDE/EIDE The IDE ( integrated device electronics) drive arrived on the early
1990s. It supports the ST-506 standard command set, and it limited controller
function build directly on the drive's logic board. Enhanced IDE ( EIDE) adds a number of improvements to the
standard IDE drives, including: Increased data throughput. Support of storage devices other than hard disk drive. Up to four IDE devices instead of just two. Support for hard disk drives larger than 528 MB.
SCSI SCSI( small computer system interface) .it is most strong
of the hard disk drive interfaces, and it is popular on network servers and high-performance workstations.
It is only one that allows both internal and external connections on the same adapter, includes a hard disk, CD–ROM scanners and tape drives.
Installation and Setup: the Five Steps
1. Physical installation and cabling2. CMOS setup3. Low-level formatting4. Partitioning5. High-level formatting
Physical Installation and Cabling
Setting the System CMOS for the Hard Disk Drive–CMOS Main Screen
Setting the System CMOS for the Hard Disk Drive–Hard Drive Setup Screen
Low-Level Formatting
Creates and organizes sectors Sets the proper interleave Establishes the boot sector
Preparing the New Drive
Create a bootable disk with formatting utilities.
Create a Microsoft Windows 98 startup disk.
Use the bootable disk to partition and format the new drive.
Partitioning
High-Level Formatting
FORMAT.COM does the following: Creates and configures the file allocation
tables (FATs) Creates the root directory
The FAT tracks which part of a file is stored on which sector.
FAT32 uses disk space more efficiently.
HW4: What is the difference between the Low-level Formatting and High-Level Formatting?
High-Level Formatting (Cont.)
Consider several factors before using FAT32. You should not use FAT32 on dual boot
systems shared by operating systems (OSs) that do not support FAT32.
FAT32 partitions that are shared can be read across the network.
FAT32 does not support compression. You should not use disk utilities that are not
made for FAT32.
Fragmentation and Compression
A hard disk can become fragmented over time.
MS-DOS, Microsoft Windows 95, Microsoft Windows 98, and Microsoft Windows Me have defragmentation programs.
Disk compression eliminates wasted cluster space.
Maintaining a Hard Disk Drive
Perform comprehensive, regularly scheduled backups.
Save a copy of the boot sector and partition table information.
Have tools on hand for hard disk repairs.
Use only disk tools certified for the hard disk drive and the OS.
Common Errors and Troubleshooting Utilities
Errors Abort, Retry, Fail Connectivity problems Lost boot and partition information CMOS errors
Utilities Scandisk SCSI BIOS disk utility
Chapter Summary Floppy disk drive technology has changed little over
the years. Floppy disk drives fail more often than any other
computer component. Installing a hard disk drive requires you to partition
the drive, set the CMOS settings, and format the drive.
The fdisk utility is used to create partitions. The geometry (CHS values) of a hard disk drive
determines its storage capacity. Partition types include primary, extended, logical,
and active. The active partition is used to initialize the OS.
