Floppy Drives

format         5 1/4       3 1/2

capacity       180KB 360KB 1.2MB   720KB 1.44MB 2.88MB

bytes per sector   512 512 512   512 512 512

sectors per track   9 9 15   9 18 36

track per side   40 40 80   80 80 80

sides       1 2 2   2 2 2

density       single double high   double high extra-high

form factor       fh fh hh/fh   hh hh hh

 

Cable:

34 wire ribbon with serial data transfer.
Red stripe designates pin 1.

 

Troubleshooting:

Light always on - cable upside down or wrong setup in CMOS.
Sporadic read/write errors - dirty heads

 

Note:

Floppy drives are factory set to "DS2". The twist in the cable tricks the system into thinking that the last drive is "DS1"
 

Record Method:

 
FM - Frequency modulation - simply records data as different polarities on media.
MFM - Modified FM
RLL - Run Length Limited - Higher track density. The "1" bit is farther apart than the "0" bit
 

 

Hard Drives

Hard drives are divided into Cylinders, tracks and sectors A track is a circular strip in the platter
A sector is a rectangular wedge in the track
A cylinder is the same track through a stack of platters
 

 
sector:prefix portion - identifies beginning / sector number
data portion - contains data
suffix - checksum
 
Sector types:
MFM drives have 17 sectors per track
RLL drives have 26 sectors per track
ESDI drives have 34 sectors per track

 
Drive components:
Disk platters old drives --> aluminum alloy
                    new drives --> glass ceramic composite
Media oxide, thin film, sputtering
Heads --
Head actuators Stepper motors - slow/unreliable
Voice coil - fast reliable
Spindle motor --
 
Drive performance:
average seek time: Time to move heads from one cylinder to another
transfer rate: speed at which data is sent to the system.
Latency: time sector becomes available after head is at track
Access time: Seek time + Latency time
 
Interleaving:
Reduced wait states due to disk rotation when reading consecutive sectors in older drives. Necessary because of slow controllers.
 
Preparing a hard drive
 

1. Low Level Format A low level FAT (physical File Allocation Table: numbering information that defines cylinder, head, sector), is written to disk. A low level format physically writes tracks and sectors to disk.

 
NEVER perform a low level format on new IDE (ATA, ATA-2). These drives are low level formatted at the factory. Low level formats are necessary for ST-506 and ESDI drives only.
 

2. Partitioning Creates an O/S file system.

FAT - DOS, WIN, OS/2, WIN NT
NTFS - Windows NT file system
HPFS - High performance file system
FAT32 - WIN 95 rel.2, WIN 98
 
Partitioning also creates a master boot record and a partition table on Sector 1 Cylinder 0 of the hard drive.
 


File System   FAT 16         FAT 32

Partition Size   <255MB <512MB <1024MB <2048MB   <8GB 8-16GB 16-32GB >32GB

Cluster Size   8 sectors (4k) 16 sectors (8k) 32 sectors (16k) 64 sectors (32k)   (4k) (8k) (16k) (32k)


 

3. High Level Format High level formats write all the necessary structures for managing files and data.
   

   VBS volume boot sector
   FAT File allocation table
   Root directory