Head Disk Interface

Question 1

Total Addressable Market (TAM) - what fraction of data is stored on HDD?

Answer 1

~2/3

June 2020 and looks like it will remain for a while

Question 2

___ of 23% for HDD and 27% for NAND (in June 2020)

Answer 2

Compound Annual Growth Rate (CAGR)

(so HDD will keep it’s 2/3 TAM

Question 3

HDDs over time:

1956: ___ MB, 70 kb/s, 50 x 24” disks (bigger than washing machine), 2 kbits/in^2, IBM “RAMAC”
1981: ___ GB, 9 x 14” disks, 12 Mbits/in^2, IBM “3380”
2005: ___ GB microdrive, 130 MB/sec, 1 x 1” disk, 105 Gbits/in^2, “Mikey”
2020: ___ TB, 3 Gb/s, 9 x 3.5” disks, ~1 Tbits/in^2

Answer 3

1956: 5 MB
1981: 1.2 GB
2005: 8 GB
2020: 20 TB

Question 4

845 x 700 x 230 um are the dimensions of what?

Answer 4

The slider

Question 5

Scaling up the HDD 1 million times would be like:
Disk ___ miles wide (covering the whole bay area)
At 7200 RPM, would be like a Boeing 787 (the head) flying at a speed of ____ (at disk’s OD)
Flying ___ above the surface
reading and writing bits smaller than the size of a human’s finger (1 x 5 cm)
Same data rate: (>2 Gbps)

Answer 5

60 miles wide
10% the speed of light
~3 mm fly height

Question 6

Spacing between the head disk interface has decreased from 200 nm in 1990 to <1 nm in current products.
1 nm is ___ (relative to hair, nitrogen atoms, or CO2 or H2O)

Answer 6

• ~1/50,000 the thickness of a human hair (50 um in diameter)
• ~3 Nitrogen atoms
• a few C02 or a few H2O molecules