DISK STORAGE

1
DISK STORAGE

• IBM 305 RAMAC, 1956
• 5 MB on 50 24-inch disks
• 9 Kbits/s transfer rate

Before 1956, computers had core memory,
multi-track mag tape, and drums.
2
Installed size of office suites and disk capacity
3
Disk jargon

• Latency seek time (to get to track) plus
• wait tune (lthalf a revolution) 2-200 ms
• Transfer rate MB/sec without arm movement
• hundreds of MB/s
• Platter One or two recording surfaces
• RPM Revolutions per minute (thousands)
• Capacity Gigabytes
• Track density
• Linear (or recording) density

4
Data is recorded on thin layer of magnetic
material
flying read and write head
Al Hoagland gns former boss
Max today 333 GB per platter 120 MB/s
transfer rate 15,000 rpm (2 ms latency)
5
Removable Winchester disk drive

• IBM 30MB 3340
• 1973
• Heads and platters
• encased in a
• sealed unit

6
36 GB 10,000 RPM, 10-platter disk (IBM)
lt1 cent per MB Storage cost 1 million percent
less than 20 years ago (67 per year) All the
heads are mounted on the same assembly, and move
together.
7
Longitudinal vs. Perspendicular recording
8
Recording Head
9
Flying read/write head (air bearing slider)
HGAHead Gimbal Assembly
http//www.hitachigst.com/tech/techlib.nsf/techdoc
s/AE7AEDB327B2E21186256D330078799B/file/Femto_whi
te_paper_FINAL_082505.pdf
10
Recording density (Gb/ in2 against year)
Compound Annual Growth Rate
11
Kryders Law growth of hard drive capacity
12
Working of hard disk

• Working of hard disk

13
Nomenclature
14
DISK GEOMETRY

• Tracks and cylinders
• Formatting marks the beginning and end of
  512-byte sectors
• (it takes up to 20
• of capacity)
• (there are far more tracks than shown)

15
Platter size

• Platter diameters
• 5.12 old PCs
• 3.74 current PCs
• 3.00 10,000 rpm drives
• 2.50 15,000 rpm drives 34MB Microdrive
• 1.80 PC card
• 1.30 obsolete PCMCIA
• 1.00 CompactFlash (cameras, pocket-PCs, )

16
Windows disk organization

• Boot Master Record (including Partition Table)
• track (cylinder) 0, side (head) 0, sector 1
• loads the operating system
• File Allocation Table (FAT)
• manages free clusters
• Root Folder (directories)
• Data Area

17
Fundamental Principles

• Tape, drum and disk storage are based on
  Faradays Law change in magnetic field induces
  voltage
• Magnetic disk is a direct-access block-storage
  device.(large capacity, fast transfer, long
  latency( O/S exploits these characteristics)
• Each bit consists of a few hundred magnetic
  grains.
• Access time limited by mechanical motion (head
  travel to track and rotational speed)
• Periphery of disk must not break the sound
  barrier.
• Recording density limited by distance to R/W
  head.Heads fly a few nanometers above surface.
• Sooner or later, solid-state storage will win out.