Embed Size (px)
Citation preview
march 15, 2010 1COCO magdisk
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.
march 15, 2010 2COCO magdisk
Installed size of office suites and disk capacity
march 15, 2010 3COCO magdisk
Disk jargon
Latency seek time (to get to track) plus
wait tune (<half 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
march 15, 2010 4COCO magdisk
Data is recorded on thin layer of magnetic material
Max today:~333 GB per platter120 MB/s transfer rate15,000 rpm(2 ms latency)
Al Hoaglandgn’s former boss
flying read and write head
march 15, 2010 5COCO magdisk
Removable “Winchester” disk drive
IBM 30MB 3340
1973
Heads and platters
encased in a
sealed unit
march 15, 2010 6COCO magdisk
36 GB 10,000 RPM, 10-platter disk (IBM)
<1 cent per MB
Storage cost1 million percent lessthan 20 years ago(67% per year)
All the heads are mounted on thesame assembly,and move together.
march 15, 2010 7COCO magdisk
Longitudinal vs. Perspendicular recording
march 15, 2010 8COCO magdisk
Recording Head
march 15, 2010 9COCO magdisk
Flying read/write head (air bearing slider)
HGA=Head Gimbal Assemblyhttp://www.hitachigst.com/tech/techlib.nsf/techdocs/AE7AEDB327B2E21186256D330078799B/$file/
Femto_white_paper_FINAL_082505.pdf
march 15, 2010 10COCO magdisk
Recording density (Gb/ in2 against year)
Compound Annual Growth Rate
march 15, 2010 11COCO magdisk
Kryder’s Law – growth of hard drive capacity
march 15, 2010 12COCO magdisk
Working of hard disk
Working of hard disk
march 15, 2010 13COCO magdisk
Nomenclature
march 15, 2010 14COCO magdisk
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)
march 15, 2010 15COCO magdisk
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, …)
march 15, 2010 16COCO magdisk
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
march 15, 2010 17COCO magdisk
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.
