Addendum to Week 9 Disk Drives

Geometry of a Drive

Microscopic bits of iron ferrite imprinted onto a piece of Mylar plastic

Arranged in concentric Circles called tracks

Each drive has a different geometry

Therefore each drive has its own controller software

Definition of head – refers to platters and not read/write heads


Each group of tracks (complete circles around spindle) on multiple platters is called a cylinder


Cluster – a group of sectors

Sectors – 512 bytes

Pie slice shape of platter – sectors bigger at edge of platter (wasted space) smaller near spindle – unusable space – measured for center of pie slice – its just right

Therefore the number of sectors per track is a fixed number from outer to inner edge of the platter on older drives  

some newer drives use the arrangement below and is hardware and manufacturer specific.


A discreet underlying structure used for arranging data on a disk.

Windows allows up to four petitions per disk. Only one can be active at a time but any one can be made active at a future time if requested. Each partition can have a separate operating system if desired


Every drive must have at least one partition but can have up to four. A DOS primary boot partition is the most prevalent and is the only kind that is bootable. Extended partitions are not bootable and have letters assigned to them as if they were separate hardware devices.

The Active partition must be a bootable partition – FDISK can change the active partition without destroying the data.

The boot sector contains five pieces of information


FAT tables (2 copies)

FAT table for each partition (if required)

Boot.ini (or io.sys)

Changing partition size using FDISK will delete all data. Partition Magic (third party software) will not destroy the data but will allow you to change partition sizes, etc.

File Systems

Hard drives will contain file systems based upon the addressing schemes outlined below

The FAT 16 systems means that there are 16 wires that can be used for addressing. This addressing limits the max size to 2 GB – Fat 16 grouped data into clusters and only gave the cluster an address and not only just the sectors.

The FAT 32 system uses 32 wires for addressing and thus allows for a larger capacity of addressing. Max disk size can be 2 Terabytes – However Windows only used 28 of the wires and therefore can only accommodate up to 32 GB drives.

2- 16th x 512 = 32MB

2- 32nd x 512 = 2 TB

2- 28th x 512 = 32 GB

MUST USE NTFS above 32 GB.

NTFS – new technology file system

32 bit addressing

used on NT, 2000, XP

Up to 2 TB

Boot sector near spindle

Always use best file system you can support in your computer

How to Identify your file system

Use FDISK on Windows 98

Right click on My Computer in all other Windows Versions

ATA – Advanced Technology Attachment

Version 1 – obsolete – used PIO Programmable I/O

Version 2 known as ATAPI – ATA Programmable Interface – Allows for other types of storage but still limited to a total of four per unit or two per interface (primary and secondary)

Really old and obsolete but in every PC made today Including SCSI motherboards

UDMA – Ultra Direct Memory Address – replacement

Speed ratings 33, 66, 100 MBPS

ATA 33 uses 40 wire IDE cable – all others use the 80 wire cable

Master is required to be at the end of the cable

80 Wire cable is color coded to motherboard

Controller is located on drive itself and not in BIOS

NOTE: All units will interoperate at different speeds but all units will act at the speed of whatever the slowest unit is.

Installing a hard drive – Jumper Pins

Jumpers are used to tell the computer which drive is the master drive (bootable) and which is a slave drive. You wish to make the boot disk the master but it is not necessary. You can boot from a slave drive but it will be slower. Somewhere on the drive will be a chart or description showing where the jumpers must be installed as required. Some drives do not need any jumpers but others may need them. Check with the label and do not assume. CS is Cable select for use with 80 wire cable.

Auto detect – all computers now use auto detect in bios to find the hard drives, cd’s etc. in the computer. In the old days, this data had to be manually entered for each drive. This is progress!

BIOS Interrupt 13 is used up to 137 GB drives

ATA Version 6 has an upper limit of 144 Petra bytes

RAID Disks – Redundant array of Independent Disks

Dynamic disks – 2 drives have one partition between them – volumes not petitions

Raids are multiple disks that work together to act as one drive (with one drive letter designation). Raid 0-6 but only 0,1, and 5 are used

Simple volume – just like a primary petition

Spanned – 1 volume spread across several disks

Striped – Raid 0 – data spread across several disks with parts of a file on different disks

Mirrored – Raid 1 - automatically copies from one disk to another

Striping with parity – Raid 5 – 3 hard drives – can recreate lost data from parity bits

Dynamic disks are a type of storage not a type of file system – system still uses fat 16, fat 32, or NTFS





Disk Cleanup

Empty Recycle bin