CHAPTER 8 MAGNETIC DRIVES
Floppy disk drives (FDD)
Hard Drives (HD)
Are types of secondary storage. Both use magnetic media to store data & operate in very much the same way.
FLOPPY DRIVES
Although largely replaced by flash drives today, floppy drives are still found in all older computer systems
Capacity of a floppy disk 1.44 MB when formatted, 3.5 inch disk
Uses a 34 pin ribbon cable with connectors for 2 drives, which are labeled as drives a & b by default. This ribbon cable
has a twist in it, the drive which has the twist between it and the FDD controller on the motherboard is drive A. pin 1 is
identified by an edge colon on the cable
Drive B was assigned to the older 5 ¼ disk, which is no longer used
Floppy drives use the BERG power connector
Hard drives use the larger molex connector
Most computers today arer shipped without floppy drives, but USB external FDD are cheap & reliable
MAGNETIC DISKS
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Magnetic disks store data in an array of circular tracks, each of which holds a number of sectors.
A sector can hold 512 bytes of data
The process that prepares a floppy disk to hold data is formatting
FLOPPY DISK FORMATTING
Done by executing format command at command prompt or using windows explorer
This creates the following
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Tracks and sectors
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Boot sector (boot record) track o, sector 1, side o (underside)
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2 copies of the file allocation table
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Root directory
The FAT is used to manage the disks, clusters or file allocation units
Floppy disks only have 1 partition
Floppy disks use the FAT file system
Floppy disks cannot store data in encrypted or compressed form using NTFS or windows explorer, you must use a 3 rd
part utility for that type of storage
HARD DRIVES
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Dominant form of secondary storage today. Multiple magnetic disks provide combined storage capacity that
can exceed 1 TB.
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Each side of a platter is sometimes called a head
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The R/W heads are moved across the platters by an actuator
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The actuator is moved by the stepper motor
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The platters are spun by the spin or drive motor
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Because hard drives are driven by z mechanical motors, they are the slowest device in a computer, or in a
network as a whole.
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All hard drives have a hard drive controller that tells the R/W heads and the actuator what to do and where to
go.
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In almost all drives today, this HD controller is integrated into the HD itself.
HARD DRIVE PREPARATION
3 steps to preparing a hard drive for use
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Low level formatting (done at the factory) creates tracks and sectors
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Partitioning – creates or changes the partition table
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High level formatting – creates fat, root directory, MBR
DRIVE INTERFACE STANDARDS
IDE – INTERGRATED DRIVE ELECTRONICS
EIDE – ENHANCED IDE
PATA – PARALLEL ATA
ARE THE SAME TECHNOLOGY
Other devices (optical & tape drives) can connect to a system using an eide connector as long as they support the
ATAPI standard.
EIDE uses an 80 conductor IDE cable, which has 40 pins, 80 wires – 40 pins to carry data with 40 additional ground
wires to reduce crosstalk.
Older IDE cables were 40 pins, 40 wires
SATA serial ata uses serial communications instead of parallel, much faster data transfer potential
CABLES –
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Take up less space
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7 pin cables
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Supports hot swapping
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But more expensive than PATA
ZBR – Zone Bit Recording
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Current method of organizing tracks and sectors
LBA – Logical Block Addressing
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Used in current hard drives to address sectors no matter where the sector is on the disk
DATA TRANSFER MODES – there are two methods for transferring data from the hard drive to memory
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DMA – Direct Memory Access (by passes CPU, faster)
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PIO – programmed input/output (does not bypass the CPU) Slower than DMA
Maximum hard drive size
Hard drive sizes are not limited by the physical amount of space on the drive, but by the system used by computer
systems to address that storage space.
Up until 1995 – 550 MB was max size
From 1995 – 2002 – 137 GB was max size, use 28 bit address scheme
2002 – ATA/100 standard uses 48 bits, allows for a max storage area of 144 petabytes
PATA – each IDE connector on the mother board can support up to 2 PATA or ATAPI devices
SATA – SATA connector supports 1 SATA device – older mother boards will have 2 data connectors. Newer mother
boards will have a mix of PATA/SATA installing a ATA controller card will increase # of connections
SCSI – small computer system interface – a technology developed in the early 90’s to allow computers (usually
servers) to use multiple devices at the same time. SCSI is a bus technology. A SCSI controller can be embedded or be
an adapter card that controls the flow of data between the computer & the devices.
BUS MASTERING – a technology that uses a secondary processor, ram & a DMA channel to perform work without
involving the CPU. SCSI uses bus mastering.
SCSI installations form a chain of devices that must be terminated on each end.
SCSI chains can support either 7 or 15 devices each device is assigned a SCSI ID and a LUN
LUN – Logical unit number
SCSI Standards make sure all devices are the same type of SCSI & from the same manufacture
SCSI 1
SCSI 2 Fast SCSI
SCSI 3 ULTR SCSI
SERIAL SCSI (SAS)
ALTERNATE TECHNOLOGIES
USB
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USB 1 .0 was too slow
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USB 1.1, 2.0 are fast enough to support hard drive connections
FIREWIRE – IEEE 1394
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Very fast serial communications
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Developed by apple
FIBRE CHANNEL
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Very expensive
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Up to 126 devices
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An improved form of SCSI
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Very fast high capacity storage, designed for servers
All of these technologies have their own connectors, & must be supported by the O.S. and motherboard to work
HARD DRIVE INSTALLATION
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Prepare for installation
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Set jumpers/dip switches if necessary
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Mount the drive in the drive bay
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Use CMOS to verify settings
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Partition and format the drive