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 COCO magdisk

Installed size of office suites and disk capacity march 15, 2010 COCO 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 COCO magdisk

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) march 15, 2010 COCO magdisk

Removable “Winchester” disk drive IBM 30MB 3340 1973 Heads and platters encased in a sealed unit march 15, 2010 COCO magdisk

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. march 15, 2010 COCO magdisk

Longitudinal vs. Perspendicular recording march 15, 2010 COCO magdisk

Recording Head march 15, 2010 COCO magdisk

Flying read/write head (air bearing slider) http://www.hitachigst.com/tech/techlib.nsf/techdocs/AE7AEDB327B2E21186256D330078799B/$file/Femto_white_paper_FINAL_082505.pdf HGA=Head Gimbal Assembly march 15, 2010 COCO magdisk

Recording density (Gb/ in2 against year) Compound Annual Growth Rate march 15, 2010 COCO magdisk

Kryder’s Law – growth of hard drive capacity march 15, 2010 COCO magdisk

Working of hard disk Working of hard disk march 15, 2010 COCO magdisk

Nomenclature march 15, 2010 COCO 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 COCO 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 COCO 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 COCO 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. march 15, 2010 COCO magdisk