Impressive and cheap storage …..
This may help you to be more forgiving if your computer goes wrong. They really are extraordinary devices. Written by Les while feeling geeky.
I have an old (mid 1990’s) metal box about 6 inches wide, 8 inches long and a little over half an inch thick. It is festooned with labels, serial numbers, bar codes and tamper-proof seals, has a bit of printed circuit board mounted into one corner and it weighs about 1kg.
Inside the box could be recorded everything I have written over the past 50 years, memos, notes, programs, letters, e-mail, shopping lists, web pages…. and there’s still plenty of room left for everything I might hope to write in the next 20 years. All in a tin box just big enough for a couple of dozen pencils.
The metal box is, of course, a computer disc drive, in this case an ‘antique’ Quantum Bigfoot 5.25 inch drive. This one is more than two decades old, it still works, and has a capacity of 2.1 gigabytes, roughly equivalent to 21 billion characters of text. The new ‘everyday’ drives that replace it are much smaller at 2.5 inches but hold five hundred times as much – 1000 gigabytes or 1 terabyte and 2, 3, or 4 terabyte drives are becoming quite common. That’s room enough not only for everything I’ve ever written but also for everything I’ve ever read or will read in a lifetime, or several lifetimes.
I shall explain disc capacity in terms of paper. Stay with me…..
A single character of unformatted text can be though of as 1 Byte (8 bits in a Byte). To keep the sums simple let us type 2500 characters onto one side of a sheet of paper and 2500 onto the reverse. That is 5000 characters or 5KB.
Ok, lets not be pedantic…. kilo stands for 1000 (k) but in binary systems a kilo is 1024 (K) but I am rounding 1024 down to 1000 for the sake of simplicity so don’t write to me to complain about my maths.
A ream of paper, 500 sheets, is about 2 inches thick and would hold 2500KB of data, better written as 2.5 MB.
My ancient 2.1GB drive has, remarkably, almost 1000 times the storage capacity of that ream of paper and could hold the data represented by a pile of paper one hundred and forty feet high, three times the height of a very tall house.
A modern 1TB drive which is much smaller in size and typically supplied in an everyday laptop computer, will hold the paper equivalence of a stack of paper 60000 feet high. Twice the height of a commercial jet aircraft. More to the point, any word or piece of data contained in that mass of 1000 billion characters is accessible in a fraction of one second…… wow!
Disc drives have never been the most glamorous components of a computer system and they are prone to fail from time to time but I hope you are now more respectful of the task they undertake as they quietly spin at anything up to 10,000 rpm.
Falling Prices:
Storing one megabyte (MB) of data in the late 1950’s cost about £5000. By the early 1980s the cost had fallen to £60, and then in the mid-1990s reached £1. The trend got steeper after that, and today the price of disc storage is thousands of times less at about 5 pence for 1000 megabytes (a gigabyte GB). Far cheaper than paper. A 1x Terabyte TB drive for your PC costs about £50 and will easily hold more than a hundred full length movies, thousands of music tracks and vast numbers of documents and photographs.
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Brief History:
The first disc drive was built in 1956 by IBM as part of a business machine called RAMAC (for Random Access Method of Accounting and Control).
The RAMAC drive was housed in a cabinet the size of a refrigerator and powered by a motor that could have run a small cement mixer. The core of the device comprised a stack of 50 aluminium platters coated on both sides with a brown film of iron oxide. The discs were two feet in diameter and turned at 1,200 rpm. The entire drive unit had a capacity of five megabytes – barely enough today for a couple of MP3 song titles.
Disc Density & Magnetism:
A disc drive records information in a pattern of magnetised regions on the disc surface.
The disc surface is made up of ‘bit cells’. Boosting the density of the disc is a matter of making the bit cells smaller and packing them closer together.
Small bit cells require small read and write heads you can’t make tiny marks with a fat crayon and the heads must be brought very close to the disc surface so that the magnetic fields cannot spread out in space.
Flying Heads:
The heads of the RAMAC drive hovered 25 micrometers above the disc on a layer of compressed air jetting from nozzles on the flat surface of the heads. Today the underside of the head is shaped to fly on the stream of air created by the spinning disc (typically 5400rpm to 7200rpm or 10000rpm or faster) and they fly very low indeed, buzzing the terrain at a height of 10 or 15 nanometers.
At this scale, a bacterial cell adhering to the disc would be like a boulder. That is why drives are assembled in ‘clean rooms’ and diy disc maintenance is not a practical proposition.
The Future…..
When conventional disc technology finally tops out, several more-exotic alternatives await. A perennial candidate is called perpendicular recording. All present discs are written longitudinally, with bit cells lying in the plane of the disc; the hope is that bit cells perpendicular to the disc surface could be packed tighter. Another possibility is patterned media, where the bit cells are predefined as isolated magnetic domains in a non-magnetic matrix. Other schemes propose thermally or optically assisted magnetic recording, or adapt the atomic-force microscope to store information at the scale of individual atoms.
What do we do with all that storage?
A few organisations have a need for colossal storage capacity. These are not mass markets. The economics of disc-drive manufacturing require selling discs by the hundred million, and that can happen only if everybody wants one.
Suppose I could reach into the future and hand you a 1-petabyte drive right now. What would you put on it? You might start by copying over everything on your present disc, all the software and documents you’ve been accumulating over the years, all your music and videos, every dvd, all your photographs, scan all your books – everything – basically your digital universe. Okay, now what will you do with the other 98% of the disc?
A cynic’s retort might be that installing the 2020 edition of Microsoft Windows will take care of the rest! “Software bloat” has reached impressive proportions but it still lags far behind the recent growth rate in disc capacity.
One certainty is that you will not fill the void with personal jottings or reading matter. In round numbers, a book is a megabyte or two. If you read one book a day, every day of your life, for 80 years, your personal library will amount to less than 30 gigabytes, which is barely noticeable. To fill any appreciable fraction of the drive with text you’ll need to acquire a major research library.
The Cambridge University Library would be a good candidate. It is said to hold 24 million volumes which would take up slightly more of your disc. Only another 90% or so still to fill.
Other kinds of information are bulkier than text. A picture, for example, is worth much more than a thousand words. For high-resolution images a round number allocation might be 10 megabytes each. How many such pictures can a person look at in a lifetime? I can only guess, but 100 images a day certainly ought to be enough for any family album. After 80 years, that collection of snapshots would add up to 30 terabytes.
What about music? A basic MP3 player will hold several thousand music tracks. Audio files run a megabyte a minute, more or less. At that rate a lifetime of listening 24 hours a day, 7 days a week for 80 years would consume 42 terabytes of disc space.
One kind of content that helps fill the disc is video. In one compressed format used for good quality HD TV, the data rate is about 1 gigabyte per hour. 1% of your available storage will hold 100,000 hours worth of movies. If you want to watch them all day and all night without a break for popcorn or other necessary comforts they will last somewhat longer than ten years. For an uninterrupted full lifetime of video you’ll have sacrifice 10% of your 1x PB storage.
The notion that we may soon have a surplus of disc capacity is profoundly counter-intuitive. A well-known corollary of Parkinson’s Law says that data, like everything else, always expands to fill the volume allotted to it.
Shortage of storage space has been a constant of human history. I have never met anyone who had a hard time filling up cupboards or bookshelves or filing cabinets.
Closets and bookshelves and filing cabinets don’t double in size every year. Now it seems we face a curious Malthusian catastrophe of the information economy. The products of human creativity grow only arithmetically, whereas the capacity to store and distribute them increases geometrically. The human imagination can’t keep up.
Or maybe it’s only my imagination that can’t keep up. I could do with a small warehouse!
Life seemed so much simpler before computers…..
Les