1. Computer Architecture CST 250
Hard Disk
Prepared by: Omar Hirzallah

2. Contents Hard disk drive Schematic picture Disk organization
File organization
Hard disk characteristics
Hard disk controllers
SAS & SATA
Encoding Schemes (MFM & RLL)

3. HARD DISK DRIVE:
Initially when hard disks were developed in 1960s, they were named as
Winchester drives. This name was not having any technical or scientific meaning, it was just a slang term.
WHAT IS A HARD DISK?
A hard disk is really a set of stacked "disks," each of which, like phonograph records, has data recorded electromagnetically in concentric circles or "tracks" on the disk. A "head" (something like a phonograph arm but in a relatively fixed position) records (writes) or reads the information on the tracks.
A hard disk/drive unit comes with a set rotation speed varying from 4800 to 15,000 rpm. Disk access time is measured in milliseconds. A hard disk drive contains rigid, disk shaped platters usually made of aluminium or glass.
The platters can’t be bend or flex as we can do in floppy. That is why it is termed as
“hard disk”. We can’t remove the platters from the hard disks in most of the cases
that is why they are also termed as “Fixed Disk”.

4. Hard Disks
                                                                                                                                                                                                                                            
The platters – are made form aluminium coated with magnetic material with glass These typically spin at 4,500 or 7,200 rpm when the drive is operating.
The arm - This holds the read/write heads and is controlled by the mechanism in the upper-left corner. The arm is able to move the heads from the hub to the edge of the drive. The arm and its movement mechanism are extremely light and fast.

5. Inside: Platters and Heads In order to increase the amount of information the drive can store, most hard disks have multiple platters. This drive has three platters and six read/write heads:

8. Disk Organization Sector Track 0 0 1 0 1 1 1 0 Cylinder
Magnetic polarity determines the bit value (1,0)
Sector
Bit Value is 1
Track
Bit Value is 0
Cylinder

9. Hard Disk Measures (performance)
Transfer rate: The data rate is the number of bytes per second that the drive can deliver to the CPU.
Seek time: is the time it takes the head to travel to the track of the disk where the data will be read or written
Capacity (Size): How many bytes we can store

10. For each zone

11. File Organization

12. File Organization
Defragmentation

13. File Allocation
File Block

14. File Allocation NTFS: New Technology File System
FAT: File Allocation Table
NTFS Boot Sector
Boot Sector
MFT 1
FAT 1
FAT 2
Data Area
Data Area
MFT Copy
Windows NT and later
Windows 95 and older
MFT : Master File Table

15. 1-Contiguous Allocation
File Allocation
1-Contiguous Allocation
Boot Sector

16. File Allocation 2- Chained Allocation(Linked list)
File Allocation Table
block
Pointer 1 7 9 13 14
FFFF
FFFF = -1
Means end of file

17. Examples Allocation(Contiguous)
File Allocation
Examples Allocation(Contiguous)
File Allocation Table
File Name
Start Block
Length
File x 2 4
File y 10 3
File z 21 7
You are required to Draw the blocks

18. Examples Allocation(Chained)
File Allocation
Examples Allocation(Chained)
You are required to Draw the blocks
File Allocation Table
block
Pointer 7 13 8 11 9 10 16 12
FFFF 15 14 …

19. Hard Disk Controllers IDE/EIDE (also called ATA)
The IDE (Integrated Device Electronics) Most new motherboards have the IDE connections built in.
Western Digital and Compaq developed the 40-pin IDE
Enhanced IDE (EIDE) adds a number of improvements to the standard IDE drives, including:
Increased transfer rate.
Support of storage devices other than hard disk drives.
Up to four IDE devices instead of just two.
ATA : Advanced Technology Attachment

20. Hard Disk Controllers SCSI
SCSI (pronounced as scuzzy) the most robust of the hard disk drive interfaces, network servers and workstations.
SCSI allowed up to 7 peripheral devices (HDD, CD-ROM, Tape, etc..) to be connected in a series to one common bus through a single controller
SCSI-2 increased that to 15 peripheral devices .
A SCSI controller uses its own BIOS and firmware to talk to its devices, then uses a software interface layer and drivers to communicate with the operating system.
Increased hard disk size
SCSI : Small Computer System Interface

21. Example SCSI Controller (Card)

22. Hard Disk Controllers ATA (IDE /EIDE) SCSI Feature 2 IDE / 4 EIDE
7/15 per channel
Devices per channel
66 MB per second (Ultra DMA)
33 MB per second (Ultra DMA)
16.7 MB per second (Fast ATA)
160 MB per second (Ultra 160)
80 MB per second (Ultra2)
40 MB per second (Wide SCSI)
Maximum potential transfer rate for
major classes of SCSI and IDE
For single devices IDE is faster
When many storage devices
are used SCSI is faster and
allows multi tasking
speed
Internal only
Internal and external
Connection types

23. SAS & SATA (Serial Attached SCSI) (Serial ATA) SAS:
an evolution of parallel SCSI into a point-to-point serial peripheral interface
enables multiple devices (up to 128) of different sizes and types to be connected simultaneously with thinner and longer cables
its full-duplex signal transmission supports 3.0Gb/s
SAS devices can communicate with both SATA & SCSI
SATA:
an evolution of the Parallel ATA physical storage interface
Serial ATA is a serial link — a single cable with a minimum of four wires creates a point-to-point connection between devices
Transfer rates for Serial ATA begin at 150MB/s
A key difference between SCSI and SAS devices:
The addition in SAS devices of two data ports, each of which resides in a different SAS domain. This enables complete failover redundancy. If one path fails, there is still communication along a separate and independent path.

24. The Encoding Schemes (MFM & RLL)
short for modified frequency modulation
an encoding scheme used by PC floppy disk drives and older Hard drives
MFM is still the standard that is used for floppy disks today
RLL:
short for Run Length Limited
an encoding scheme used to store data on newer PC hard disks
RLL produces fast data access time and increases a disk's storage capacity by up to 50 percent over the older encoding scheme MFM
Technically, any disk drive can use MFM, RLL, or some other encoding scheme but the one used depends on the integrate disk controller within the disk drive

25. References
Mano, (2008). Logic and Computer Design Fundamentals, 4th ed., Prentice-Hall. Mano, (2006),Digital Design, 4th ed, Prentice Hall. Kifer, M., &Smolka, S. A. (2007).Introduction to Operating System Design and Implementation, Springer memory.asp‏ en.wikipedia.org/wiki/Bus_(computing) en.wikipedia.org/wiki/Addressing_mode‏