So, how big is an exabyte?

[Pedersen]

Wouldn't USB or SD be more space-efficient than DVDs?
Of course, I may be wrong, and even if I'm right your point about an exabyte being huge still stands.

Oh, I'm sure it would. You could even chop the sizes in half (I think) by going with dual layer DVDs. However, somebody else did the math and figured out how much data one 747 can carry, and I just used what they came up with. I didn't feel like figuring out the bandwidth of a 747 for any specific media type on my own

Holy crap, I can't even wrap my mind around that one.

That's the point. It's such a mind-bogglingly huge amount of data, and we're heading towards being able to store it. It amazes me how far we've come, especially when I consider my very first computer. It was a Commodore Vic-20. When it started up, it told me that it had 3353 bytes free. I could get an 8K memory expansion pack for a couple hundred bucks. Now? I wouldn't take such a thing off your hands unless you paid me enough to cover the recycling fees and my time to take it to the recycling center.

And that's only assuming the "marketing" format of an exabyte which is done in base 10, as opposed to the technical format which is a base 2. It has a tendency of being very different numbers the higher up you go.

Well, on the other hand, there's a push to use a new standard, the bibyte for powers of 2. This would give KiB, MiB, GiB, TiB, PiB, and EiB when we need it. I can understand the desire. *shrug*

The first hard drive I worked with had a capacity of 173,328 bits. Built by Singer for the Minuteman missiles. 8" platter, 2-3 PC boards on top of the platter and a doubled-fist sized motor under it.

We used it to store 6-bit brightness values for stage lighting 80-200 channels, 200 cues. (circa 1970-1977)

That would mean you were dealing with a hard drive that could store only 28KiB of data (assuming a 6 bit byte, which was common enough before the computing industry decided that a byte would be 8 bits). Considering that an 8" floppy disk could store 79.7KiB back in 1971, I suspect that your units might be wrong, or that the time of manufacture you mention might be wrong.

First computer I had (and still do) was a TI 99-4/A. No hard drive, 16 bits of memory...just enough to play Attack or TI Invaders

Ummm... I rather suspect that this was meant to be 16K, not bits, since 16 bits would be only two bytes by the time the TI99 4/A arrived on the scene. Quite a few low level instructions required two bytes to do anything on the computer, so a machine with only two bytes would have been completely useless. And Wikipedia seems to back me up on this.

Still 16K for the time was impressive. Could do a lot with it.

[dalesys]

Pedersen, the company (now defunct) was Electro-Controls (Control Lighting in Canada) and that data size is right (I had mis-remembered it as up to 1.8M until I researched the Minuteman control system & multiplied out the data that the D/A converters in the system used).

I worked there as an engineering tech 1973-1977, just as microprocessors were starting to be evaluated.

I worked on systems with that hard drive in theatres in Winnipeg, Banff, Northern Alberta Centennial (Edmonton), Queen Elizabeth (Vancouver) and Samford University (Homewood AL). There were at least three others: one in Quebec and two in Wisconsin: WSU:Whitewater & WSU:Superior.

I was also the R&D/Engineering tech assigned to come up with an emergency replacement when Samford proved that that hard drive was intended to run continuously, not just for 6 weeks spring & fall. I kludged up ann interface to an 8" SSSD floppy that just read/wrote raw data to the drive.

The logic was built using a mix of DTL (9000) & TTL (7400) logic, mostly SSI gates, some MSI chips on hand-wired boards about 8x12 inches. The same size board was used for a triple 2-channel 6-bit d/a converter to control 3 dimmer channels. The Edmonton system had 120 stage light dimmers & 40 D/A boards... and a 100A 5V linear power supply.

I was in the meetings when a startup company named Zilog came around puffing their new improved Z80! I had a first edition Z80 databook from that.

[MadMike]

Damn, just think of the server I could have with one of those.

I'm currently running a RAID-5 with 5.25 terrabytes, which of course Pedersen already knows.

[Bandit]

The first hard drive I bought was 250 Meg for $250.

I just picked up a 1.5 Tb for $89.

On (and in) my desktop computer, I have more storage than the tape library that I worked in on one of my first jobs.

Still, an exabyte of storage would be great for <ahem> usenet downloads.

That said, I still adore my Commodore 64 (and M.U.L.E. and Jumpman)

B

[Spiffy McMoron]

So, in basic terms, it would hold about the whole world's supply of on-line pr0n.

You clearly underestimate the world's supply of porn.

<snip>A whole bunch of really badass facts</snip>

That's a lot of data. Damn. And we're heading towards being able to store that much data within my lifetime.

And to think that some people can't figure out how to use a PowerPoint. This doesn't bode well for them.

[HYHYBT]

I've got one machine with a 2-terabyte RAID-5 array. It's made out of five identical 500GB disks - remembering that with RAID-5, one disk worth of space is used for coping with a future disk failure.

Is there any way, using plain ordinary English, to explain how that works, for idiots such as myself who can't imagine any way to keep everything safe without a second copy of everything?

edit: and after a short trip to the bathroom, I realized how it could be done... or at least, one way.

[Pedersen]

Pedersen, the company (now defunct) was Electro-Controls (Control Lighting in Canada) and that data size is right (I had mis-remembered it as up to 1.8M until I researched the Minuteman control system & multiplied out the data that the D/A converters in the system used).

I stand corrected. Damned small hard drive

Is there any way, using plain ordinary English, to explain how that works, for idiots such as myself who can't imagine any way to keep everything safe without a second copy of everything?

I don't know how easy it will be to explain, but I will try.

In a typical RAID5 array, one drive is set aside for what's called parity check. A parity check uses a function called XOR to to calculate a one-bit checksum of other bits. To explain it, and how it's different, requires knowing a total of 3 other functions. Note that for all computer functions, they take (at the very lowest level, which is where we care about XOR) either 1 or 0 as input, and return either 1 or 0.

AND(X,Y): This returns 1 if both X and Y are 1. Otherwise, it returns 0.
OR(X,Y): This returns 1 if either X or Y are 1. Otherwise, it returns 0.
NOT(X): This returns 1 if X is 0. Otherwise, it returns 0.
XOR(X,Y): This returns 1 if exactly one of (X,Y) is 1. Otherwise, it returns 0. One or the other, but not both, in other words.

Every byte in a computer is made up of a string of 8 bits. When doing an XOR on two whole bytes, each bit in byte 1 is XOR'ed with the corresponding bit in byte 2. This produces a third byte, which is called the parity byte. That byte is then written to the parity drive at the same location as the first two bytes were going to be written.

The upshot of all of this is that the third drive acts as a checksum. It allows the RAID controller to track the status of the individual bits. When a drive dies, the RAID controller can then notify the OS, which can then notify the admin. Furthermore, due to the nature of XOR, the RAID controller can continue using the data. It just has to recompute what the value should have been.

When a new drive is installed to replace the dead drive, it figures out what the values are for every location on disk using the good drive and the parity drive. The end result is a system that is resistant to any one drive failure. If two go in the same array, though, you're screwed.

Anyway, I hope that made some sense.

[r2cagle]

. Anyway, I hope that made some sense.

Not to me, but that's okay. That's why you deserve the big bucks! Deserve - being the operative word.

[Midorikawa]

That's actually probably the best explanation of RAID5 I've seen. Granted, I already knew how it works, and use it daily at work, and will use it at home as soon as I get more computer moneys:

Filesystem      Size   Used  Avail Capacity  Mounted on
/dev/disk3s2   201Gi  167Gi   34Gi    84%    /
/dev/disk4     698Gi  685Gi   12Gi    99%    /Volumes/Data

...because that much data in a RAID0 is just a bad idea. :-)

Not to me, but that's okay. That's why you deserve the big bucks! Deserve - being the operative word.

Basically, it uses a third drive as a parity drive in case of drive failure, so in a 3 drive array, 2 drives are striped, 3rd is parity. If you take nothing else out of it, this is the important part: It allows for any 1 drive to fail with no loss of data.

[Geek King]

That said, I still adore my Commodore 64 (and M.U.L.E. and Jumpman)

B

Ahem,

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