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.
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COCO magdisk

2. Installed size of office suites and disk capacity
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COCO magdisk

3. Disk jargon Latency seek time (to get to track) plus
wait tune (<half a revolution) 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
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COCO magdisk

4. Data is recorded on thin layer of magnetic material
flying read and write head
Al Hoagland
gn’s former boss
Max today:
~333 GB per platter
120 MB/s transfer rate
15,000 rpm
(2 ms latency)
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COCO magdisk

5. Removable “Winchester” disk drive
IBM 30MB 3340
1973
Heads and platters
encased in a
sealed unit
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COCO magdisk

6. 36 GB 10,000 RPM, 10-platter disk (IBM)
<1 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.
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COCO magdisk

7. Longitudinal vs. Perspendicular recording
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COCO magdisk

8. Recording Head
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COCO magdisk

9. Flying read/write head (air bearing slider)
HGA=Head Gimbal Assembly
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COCO magdisk

10. Recording density (Gb/ in2 against year)
Compound Annual Growth Rate
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COCO magdisk

11. Kryder’s Law – growth of hard drive capacity
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COCO magdisk

12. Working of hard disk
Working of hard disk
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COCO magdisk

13. Nomenclature
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COCO magdisk

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)
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COCO magdisk

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, …)
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COCO magdisk

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
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COCO magdisk

17. Fundamental Principles
Tape, drum and disk storage are based on Faraday’s 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.
march 15, 2010
COCO magdisk