5 Dec
2014
5 Dec
'14
8:59 a.m.
I have had my PDP-8 (no letter) since around 1985. As part of the deal I
got a little over 200 DECtapes. Most of these are SCOTCH 3M branded in
cardboard boxes and not DEC branded DECtapes in the clear blue plastic
containers. I have been thinking about moving this data to a permanent
storage location so I wondered how much space this would require. Turns
out to be about 57 million bytes and that would be without bothering to do
any compression.
The trivia question is:
Approximately how many DECtapes will fit on a single one terabyte drive?
As there are several possible answers to this feel free to reply on the
list. I will give my answer in a few days.
Doug Ingraham
5 Dec
5 Dec
9:02 a.m.
On Fri, 5 Dec 2014, Doug Ingraham wrote:
Approximately how many DECtapes will fit on a single
one terabyte drive?
As there are several possible answers to this feel free to reply on the
list. I will give my answer in a few days.
Physically, or data-wise? ;)
Doug Ingraham
--
Cory Smelosky
http://gewt.net Personal stuff
http://gimme-sympathy.org Projects
9:06 a.m.
It depends how you stack them.
On Fri, Dec 5, 2014 at 11:02 AM, Cory Smelosky <b4 at gewt.net> wrote:
On Fri, 5 Dec 2014, Doug Ingraham wrote:
Approximately how many DECtapes will fit on a single one terabyte drive?
As there are several possible answers to this feel free to reply on the
list. I will give my answer in a few days.
Physically, or data-wise? ;)
Doug Ingraham
--
Cory Smelosky
http://gewt.net Personal stuff
http://gimme-sympathy.org Projects
9:24 a.m.
On Fri, Dec 05, 2014 at 09:59:59AM -0700, Doug Ingraham wrote:
The trivia question is:
Approximately how many DECtapes will fit on a single one terabyte drive?
As there are several possible answers to this feel free to reply on the
list. I will give my answer in a few days.
This has been up on the list before :) Entertaining nontheless.
My answer: all of them!
Cheers,
Pontus
3:05 p.m.
tony duell wrote:
Approximately
how many DECtapes will fit on a single one terabyte drive?
All that were ever made?
3:21 p.m.
From: Jerome H. Fine
Sent: Friday, December 05, 2014 3:05 PM
> tony duell wrote:
>> Approximately how many DECtapes will fit on a
single one terabyte drive?
> All that were ever made?
If I remember correctly, a TU-58 tape holds 512 blocks
of 512 bytes
or 262,144 bytes in total or 2 ** 18 bytes
Jerome, "DECtape" without a following "II" refers to *real* DECtape,
the
3/4" medium used on DEC's 555, TU-55 and TU-56 DECtape drives. These were
formatted with 578 blocks of 256 18-bit words (even for the PDP-11, which
ignored bits 0 and 1) or 1102 blocks of 129 12-bit words (= 86 18-bit words)
depending on which architecture the drives were connected to.
These were 4" reels, not cassettes.
Rich
Rich Alderson
Vintage Computing Sr. Systems Engineer
Living Computer Museum
2245 1st Avenue S
Seattle, WA 98134
mailto:RichA at LivingComputerMuseum.org
http://www.LivingComputerMuseum.org/
6 Dec
6 Dec
4:36 p.m.
Rich Alderson wrote:
From: Jerome H. Fine
Sent: Friday, December 05, 2014 3:05 PM
Jerome, "DECtape" without a following "II" refers to *real*
DECtape, the
3/4" medium used on DEC's 555, TU-55 and TU-56 DECtape drives. These were
formatted with 578 blocks of 256 18-bit words (even for the PDP-11, which
ignored bits 0 and 1) or 1102 blocks of 129 12-bit words (= 86 18-bit words)
depending on which architecture the drives were connected to.
These were 4" reels, not cassettes.
If my arithmetic is still correct, all of the effective capacities of
the DECtape usage were less than 300,000 bytes. Please
correct me if I am wrong.
And regardless of all of the questions AND INTERPRETATIONS
of the actual capacity of a one terabyte drive, the final capacity of a
such a drive after a Low Level Format would be over 3 million tapes
or the same answer I gave last time. Since the TU-55 tape has only
about 13% more capacity than a TU-58 tape, that answer was
expected.
Note that I assume ABOUT 25% reduction in capacity between
the unformatted and formatted drive.
So again, it seems likely (probably more so for DECtape) that DEC
produced less than 3 million tapes which means that Tony Duell's
answer is correct.
As for all the chatter that I seemed to have produced over
terabyte = 2 ** 40
and
terabyte = 10 ** 12
at least I defined my assumption and everyone knew the standard being
used. As for the reason for the different standards, even they are a
trivial
aspect of the marketing lies which are often used to hype and market
hardware and software. So I suggest that we all just accept that both
of the standards are valid as long as they are clearly defined since at
present memory and hard drives seem to use different definitions that
have been accepted for a number of years. I would point out that one
reason that memory may have stayed with 2 ** 30 is that memory is
usually produced and sold in multiples of 2 ** 30 these days whereas
hard drives are all over the map and almost never such a simple multiple.
Please don't use the previous paragraph to start the conflict all over
again.
Jerome Fine
tony duell
wrote:
If I remember correctly, a TU-58 tape holds 512 blocks of 512 bytes
or 262,144 bytes in total or 2 ** 18 bytes
Approximately how many DECtapes will fit on a
single one terabyte drive?
All that were ever made?
5 Dec
5 Dec
4:09 p.m.
On Fri, Dec 05, 2014 at 06:05:20PM -0500, Jerome H. Fine wrote:
[...]
Assuming that 1 terabyte is 2 ** 40 bytes [...]
It's not, it's 10**12. Every other use of SI multipliers are powers-of-ten,
and computers are not special little snowflakes entitled to be different.
As it happens, a disk with a nominal capacity of 1TB will actually contain
exactly 1,000,204,886,016 bytes[0], which is a quite curious number. Unless
I've screwed up my maths, the capacity of a drive with a nominal capacity of X
TB is exactly 1,000,194,048,000X + 10,838,016 bytes.
Those numbers factorise to 2**17 * 3**3 * 5**3 * 7*17 * 19 and 2**13 * 3**3 *
7**2 respectively. Now they're going to be divisible by 2**12 as that's the
sector size, but the remaining factors do not suggest any obvious rounding-off
boundary.
[0] The data sheet I have for Seagate's 1TB ST1000DM003 gives its capacity as
1,953,525,168 (512-byte) sectors, with the other disks sharing the data
sheet also having sector counts ending in 168. WD's data sheet for the 1TB
WD10EZEX claims 1,953,525,169 sectors, but the other disks on that data
sheet have sector counts ending 168 and 448. I thus believe the 169 to be
a typo of 168, as it would mean that the disk's capacity is not a multiple
of the 4096-byte sector size typical of large disks.
It is increasingly-rare to find exact capacities on data sheets, so I have
not checked against other manufacturers, but I gather that they have all
agreed to give their disks the same geometry for a given nominal advertised
capacity.
4:20 p.m.
On Dec 5, 2014, at 4:09 PM, Peter Corlett <abuse at
cabal.org.uk> wrote:
On Fri, Dec 05, 2014 at 06:05:20PM -0500, Jerome H. Fine wrote:
[...]
[snip]
Assuming that 1 terabyte is 2 ** 40 bytes [...]
It is increasingly-rare to find exact capacities on data sheets, so I have
not checked against other manufacturers, but I gather that they have all
agreed to give their disks the same geometry for a given nominal advertised
capacity.
The reason for that is primarily for spares. Since the interfaces now in use are
LBA based, the drive when it detects a bad sector is free to reallocate the sector
from its spares pool. This simplifies software in that
it doesn't have to manage
bad blocks...the drive does it. How much space is
reserved on the drive is decided
by the manufacturer. Usually there are some number of spare sectors allocated
to the cylinder itself and then there are entire spare cylinders.
The drive manufacturers don't agree on geometry. You don't see it because
it's
all hidden behind the LBA interface.
Drive capacity (and drive cost) is driven by 2 fundamental things: number of platters
and number of heads. Yes, there are others such as quality of the media and motor,
but within a family the media and motor are common.
A drive manufacturer will "de-rate" a drive by not putting in all of the heads.
Actually
a family of drives is 1, 2 (or sometimes 3) platters and 2n or 2n-1 heads (where n is
the number of platters).
TTFN - Guy
7:13 p.m.
Assuming that
1 terabyte is 2 ** 40 bytes [...]
It's not, it's 10**12. 
7:55 p.m.
On Fri, Dec 5, 2014 at 8:13 PM, Mouse <mouse at rodents-montreal.org> wrote:
Nor any less.
NIST, IEC, and ISO will tell you that using SI prefixes for powers of
two is wrong. I suspect that Standards Council of Canada will as
well, but I haven't looked into it.
On the other hand, disk drive vendors will tell you that they define
KB, MB, GB, and TB as 10^3, 10^6, 10^9, and 10^12 bytes, respectively.
If you buy their 1TB drive expecting to get 1024^4 bytes of storage,
you'll be disappointed, and you likely won't have any legal recourse
because the vendor puts that definition in all of their marketing
literature and on the product packaging.
So who is right, disk drive vendors or the standards bodies? It's a de
facto vs. de jure distinction.
It's not,
it's 10**12.
You don't get to tell us how we use language any more than
anyone else
does. (For that matter, if you buy a
"4G" stick of RAM, would you be perfectly happy to get one containing
no more than 4,000,000,000 bytes?
I make a point of buying 4 GiB DIMMs rather than 4 GB. The gibi
prefix (defined as 1024^3) is part of the International System of
Quantities (ISQ, ISO/IEC 80000-13:2008). SI ("the metric system"),
which defines the decimal prefixes, is also part of ISQ.
8:12 p.m.
On 2014-12-06 04:13, Mouse wrote:
You don't get to tell us how we use language any more than anyone else
does. Lots of words and phrases have technical meanings in hackish
English different from the meanings the same words carry in mainstream
English; this is just one more example. (For that matter, if you buy a
"4G" stick of RAM, would you be perfectly happy to get one containing
no more than 4,000,000,000 bytes? You make it sound as though you
would - but I find that doubtful.)
While you have a half point, Mouse, the fact is that for disk
capacities, the standard is actually to use K to mean 10^3 and not 2^10,
so Fred is absolutely right.
Assuming that 1 terabyte is 2 ** 40 bytes [...]
It's not, it's 10**12. Or, of course, you can continue to insist on
misunderstanding
long-established uses.
See above. In this case, that is the long-established rule.
(The reason have been suggested in the past that disk manufacturers
started this odd practice (odd for computers that is) a long time ago
since it allowed them to write higher numbers, which looked better for
marketing purposes...)
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
8:35 p.m.
Assuming that
1 terabyte is 2 ** 40 bytes [...]
It's not, it's 10**12. from that era (and even on some drives), saying things
like "based on
1GB = 1 billion bytes", which, if the metric meanings were
indeed the
standard you seem to be claiming they were, would not have been worth
mentioning.
/~\ The ASCII Mouse
\ / Ribbon Campaign
X Against HTML mouse at rodents-montreal.org
/ \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B
9:14 p.m.
On 2014-12-06 05:35, Mouse wrote:
While you have a half point, Mouse, the fact is that for disk
capacities, the standard is actually to use K to mean 10^3 and not
2^10, so Fred is absolutely right.
"The standard"? That disagrees with my experience. I have numerous
disks from the days when capacities were several tens of megabytes, or
low hundreds of megabytes; they are all labeled accurately. Somewhere
around the time of single-digit gigabyte capacities, disk manufacturers
started mislabeling their disks. That they were doing so knowing it
was an actively misleading practice is evidenced by the notes in ads
from that era (and even on some drives), saying things like "based on
1GB = 1 billion bytes", which, if the metric meanings were indeed the
standard you seem to be claiming they were, would not have been worth
mentioning.
Well, since single digit gigabyte disks have been around for at least 20
years now, I think it's safe to say that it now is the "standard".
As much as I dislike it, I've come to accept it.
And I mentioned it as well, it was a dirty trick to be able to write
higher numbers in their marketing...
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
> Assuming
that 1 terabyte is 2 ** 40 bytes [...]
It's not, it's 10**12.
You don't get to tell us how we use language
any more than anyone
else does. [...] 
9:18 p.m.
"based on 1GB = 1 billion bytes"
There are even, historically, disputes on what a "billion" is!
(a thousand million V a million million)
If "kibi", "mebi", "gibi", [what is T?] were to have been
introduced half
a century earlier, then we wouldn't have this ongoing silly fight!
But, does ANYBODY feel that there is any justification for "Megabyte"
being calculated as 10^3 * 2^10 ??!? (1024,000)
That is what is used, and the only way to come up with a 1.4M floppy being
"1.44MB". For those not arithmetic challenged, multiply 80 * 2 * 18 * 512
--
Grumpy Ol' Fred cisin at xenosoft.com
6 Dec
6 Dec
6:02 a.m.
On Fri, Dec 05, 2014 at 11:35:54PM -0500, Mouse wrote:
[...]
"The standard"? That disagrees with my
experience. I have numerous disks
from the days when capacities were several tens of megabytes, or low hundreds
of megabytes; they are all labeled accurately.
My ratty old tiny disks are all in storage so I can't pull a few out and check
the CHS/LBA versus the marked capacity, but I note that When it comes to mere
megabytes, 1000**2 and 1024**2 are still close enough for it to be lost in
rounding errors.
Somewhere around the time of single-digit gigabyte
capacities, disk
manufacturers started mislabeling their disks. That they were doing so
knowing it was an actively misleading practice is evidenced by the notes in
ads from that era (and even on some drives), saying things like "based on 1GB
= 1 billion bytes", which, if the metric meanings were indeed the standard
you seem to be claiming they were, would not have been worth mentioning.
Actually, the notes in the ads were added later due to litigious bastards and
other chancers claiming that they believed it to mean powers-of-two and making
a nuisance of themselves in court.
This power-of-two confusion is an artifact of how solid-state memory devices
are made, and does not apply to everything vaguely related to computers.
Otherwise one could try and argue that a "dozen eggs" should contain 13 eggs
because bakers add an extra loaf to a batch as an artifact of the bread-making
process.
Consider also the infamous 1.44MB disk. That number comes from 1440 * 1024, so
apparently a megabyte is *also* 1,024,000 bytes. If we can humpty-dumpty it
and pluck numbers out of the air, why not just call a megabyte 3,141,592 bytes?
10:48 a.m.
On 2014-12-06 15:02, Peter Corlett wrote:
Once upon a time, disks actually were also given their size in powers of
two, so no, I'm pretty sure you are wrong about the order of things.
That would would have thought the size were in powers of two were
natural. At some point, some clever marketing people realized that if
they changes to actually use the power of ten prefixes instead, they
could inflate their numbers, and fool those poor suckers who still
thought the numbers were powers of two. Thus upping one on their
competitors as well. Of course, it didn't take long for the competitors
to just copy that idea, and there we are today...
On Fri, Dec 05, 2014 at 11:35:54PM -0500, Mouse
wrote:
[...]
For megabytes, the difference isn't that big, true. When you get to
gigabytes it starts becoming significant, and when we talk terabytes, if
definitely more than a rounding error.
For one terabyte, the difference is close to 10 gigabytes...
(For one meg, the difference is 48K).
"The standard"? That disagrees with my
experience. I have numerous disks
from the days when capacities were several tens of megabytes, or low hundreds
of megabytes; they are all labeled accurately.
My ratty old tiny disks are all in storage so I can't pull a few out and check
the CHS/LBA versus the marked capacity, but I note that When it comes to mere
megabytes, 1000**2 and 1024**2 are still close enough for it to be lost in
rounding errors. Somewhere
around the time of single-digit gigabyte capacities, disk
manufacturers started mislabeling their disks. That they were doing so
knowing it was an actively misleading practice is evidenced by the notes in
ads from that era (and even on some drives), saying things like "based on 1GB
= 1 billion bytes", which, if the metric meanings were indeed the standard
you seem to be claiming they were, would not have been worth mentioning.
Actually, the notes in the ads were added later due to litigious bastards and
other chancers claiming that they believed it to mean powers-of-two and making
a nuisance of themselves in court. This power-of-two confusion is an artifact of how
solid-state memory devices
are made, and does not apply to everything vaguely related to computers.
Otherwise one could try and argue that a "dozen eggs" should contain 13 eggs
because bakers add an extra loaf to a batch as an artifact of the bread-making
process.
Uh... Not sure where the eggs enter into my computer, though...
The power-of-two issue is not because of how solid state disks work, but
how computers work. In general, you *always* means things in powers of
two in computers. The exception nowadays being disks. But main memory,
cache, speeds, are all measured in powers of two.
Actually, I should say, everything related to data. Anything that
originates with a bit.
Frequencies are not power of twos, for instance.
Consider also the infamous 1.44MB disk. That number
comes from 1440 * 1024, so
apparently a megabyte is *also* 1,024,000 bytes. If we can humpty-dumpty it
and pluck numbers out of the air, why not just call a megabyte 3,141,592 bytes?
Actually, the 1.44MB floppy holds 1,474,560 bytes.
512 bytes per sector, 18 sectors per track, 80 tracks per side, and two
sides... Where did you pull the 1440*1024 from???
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
10:54 a.m.
On 2014-12-06 19:48, Johnny Billquist wrote:
On 2014-12-06 15:02, Peter Corlett wrote:
I should actually do my math before commenting. :-)
It just happens, that by a funny accident, 1440*1024 is actually 1,474,560.
But still. The actual size of the floppy wasn't decided because you
pulled out 1440*1024, but because of the format of the darn thing.
1.44MB is just the closest "nice" number you can come up with after the
fact as a way to talk about the capacity of the thing.
It is not an exact number, but they seldom are, when we talk about
storage. People like to round things off, to make it easier to talk about.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
Consider also the infamous 1.44MB disk. That
number comes from 1440 *
1024, so
apparently a megabyte is *also* 1,024,000 bytes. If we can
humpty-dumpty it
and pluck numbers out of the air, why not just call a megabyte
3,141,592 bytes?
Actually, the 1.44MB floppy holds 1,474,560 bytes.
512 bytes per sector, 18 sectors per track, 80 tracks per side, and two
sides... Where did you pull the 1440*1024 from???
12:40 p.m.
On Sat, 6 Dec 2014, Johnny Billquist wrote:
I should actually do my math before commenting. :-)
It just happens, that by a funny accident, 1440*1024 is actually 1,474,560.
But still. The actual size of the floppy wasn't decided because you
pulled out 1440*1024, but because of the format of the darn thing.
1.44MB is just the closest "nice" number you can come up with after the
fact as a way to talk about the capacity of the thing.
It is not an exact number, but they seldom are, when we talk about
storage. People like to round things off, to make it easier to talk about.
It is NOT a "nice" number.
Honest numbers would be either 1.47 or 1.4
There is no legitimate way to come up with 1.44 unless you cheat and MIX
powers of 10 and powers of 2.
11:26 a.m.
On 12/06/2014 10:48 AM, Johnny Billquist wrote:
Actually, the 1.44MB floppy holds 1,474,560 bytes.
512 bytes per sector, 18 sectors per track, 80 tracks per side, and two
sides... Where did you pull the 1440*1024 from???
These are primarily PC distinctions. The HD 3.5" disk is sold with a
nominal raw capacity of 2.0MB. In other words, if you assume a 300 RPM
spindle speed and 500KHz clock, a track will hold about 12,500 bytes
using MFM. Drives are specified for 80 (double-sided) cylidners, so you
get exactly 2,000,000 unformatted bytes on a disk. So far so good.
But a "360K" 5.25" disk is formatted in PC terms as tracks of 9 sectors
of 512 bytes or 720 sectors total or exactly 360 * 1024 bytes. So far
so good.
Now, if we extend this to the "1.2MB" disk with 15 sectors of 512 bytes
per track, we run into a problem. Counting only one side, we have
15*512*80 = 600,000 bytes. Making this double-sided is 1,200 * 1024,
which was 1.2 * 1,000 * 1024--a mongrel. I prefer to call this
1200K--and it's 3.5" cousing 1440K--and indeed some Microsoft utilities
access this--but the world is what it is.
The drive, btw, is no more 1.44MB than is the format. Various
manufacturers have placed more or less on the floppies, dependent on
format and spindle speed.
I take hard drive capacities as stated as more-or-less; not exact. It's
been the case since the manufacturers started putting printed defect
maps on the drives.
FWIW, sectors sizes of other than powers-of-two have been well-known for
a long time. CDC Cyber used 644 6-bit characters The Zilog
development system employed 132 bytes per sector on 8" floppies. Older
decimal-based machines often used sector lengths that were a multiple of 10.
--Chuck
11:51 a.m.
On 12/06/2014 11:26 AM, Chuck Guzis wrote:
Finger-brain disconnect: Should be:
Now, if we extend this to the "1.2MB" disk
with 15 sectors of 512 bytes
per track, we run into a problem. Counting only one side, we have
15*512*80 = 600 * 1024 bytes. Making this double-sided is 1,200 * 1024,
which was 1.2 * 1,000 * 1024--a mongrel. I prefer to call this
1200K--and it's 3.5" cousing 1440K--and indeed some Microsoft utilities
access this--but the world is what it is.
12:48 p.m.
On Sat, 6 Dec 2014, Chuck Guzis wrote:
These are primarily PC distinctions. The HD 3.5"
disk is sold with a
nominal raw capacity of 2.0MB. In other words, if you assume a 300 RPM
Yes, we are talking about "formatted capacity" with a very arbitrary
format.
Q: which manufacturer called their 2.8M drive "4M", and quoted the
unformatted capacity?
But a "360K" 5.25" disk is formatted in
PC terms as tracks of 9 sectors
of 512 bytes or 720 sectors total or exactly 360 * 1024 bytes. So far
so good.
. . . and, of course, other choices of format parameters, even sticking
with MFM, can lead to 300K to 440K.
"360K" became a relatively unambiguous way to describe it, so long as one
acknowledges that that is in terms of the most prevalent format in use.
I take hard drive capacities as stated as
more-or-less; not exact. It's
been the case since the manufacturers started putting printed defect
maps on the drives.
It was always interesting to note that FDISK used Mebibytes, wheras other
utilities in the same OS used 1,000,000, or even the bizarre 1,024,000
9:40 p.m.
On 2014-12-06 20:38, Antonio Carlini wrote:
On 06/12/14 18:48, Johnny Billquist wrote:
Ouch, got me. I was thinking of network speeds, and for a moment when
composing I got the idea that they were. Of course, they are not.
So it's only storage that naturally lends itself to powers of two,
except of course that disks don't. :-)
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
Actually, I should say, everything related to
data. Anything that
originates with a bit.
Frequencies are not power of twos, for instance.
Network speeds are not powers of two either.
12:38 p.m.
> Consider also the infamous 1.44MB disk. That
number comes from 1440 * 1024, so
> apparently a megabyte is *also* 1,024,000 bytes. If we can humpty-dumpty it
> and pluck numbers out of the air, why not just call a megabyte 3,141,592 bytes?
On Sat, 6 Dec 2014, Johnny Billquist wrote:
Actually, the 1.44MB floppy holds 1,474,560 bytes.
512 bytes per sector, 18 sectors per track, 80 tracks per side, and two
sides... Where did you pull the 1440*1024 from???
1,474,560 IS, indeed 1440 * 1024
If you use powers of 10, it would be 1.47 M.
If you use powers of 2, it would be 1.40624 M.
SO, how did they get "1.44 M"?
(rhetorical question; don't you hate rhetorical questions?)
In order to get "1.44", they stated that it was 1440 Kilobytes, (where
"kilobyte" was the traditional COMPUTER meaning of 1024.
Then they divided 1440 by 1000, to get 1.44.
They defined "Megabyte" to be 1000 kilobytes (1024)!
Therefore, they divided by 1024 AND divided by 1000.
You can make a case for powers of 10;
you can make a case for powers of 2;
it takes marketing assholes to mix them.
If you round to "1.4 M", then at least it doesn't pin the needle on the
bogusimeter.
The ST506, when formatted with 512 byte sectors, was 306 * 2 * 17 * 512
for 5326848 5326Ksi 5202Kibi 5.33Msi 5.08007815Mebi
The ST412, when formatted with 512 byte sectors, was 306 * 4 * 17 * 512
for 10653696 10653Ksi 10404Kibi 10.4 Msi 10.16015625 Mebi
In those days, the rounding wasn't a big problem, and either set of units
would do.
NOTE: In contrast with modern marketing, Seagate did NOT try to
"maximize" the numbers by changing units nor using extraneous
"significant" digits.
They called the 506 a "5 Megabyte drive", NOT "5.33" nor
"5.08".
They called the 412 a "10 Megabyte drive", NOT "10.4" nor
"10.16".
'course part of that was the higher prevalence of bad sectors.
If'n you buy a "10.4 Megabyte" drive and it ends up formatting to 10.2
(due to some bad sectors), you gripe about the quality.
OTOH, if you buy a "10 Megabyte drive", and it formats to 10.2, then you
brag to all of your friends about what a great drive you got.
(and Seagate gets a better reputation)
[for some value of indeterminate "you", not speaking to Eric or Tony]
--
Grumpy Ol' Fred cisin at xenosoft.com
12:46 p.m.
NOTE: In contrast with modern marketing, Seagate did
NOT try to
"maximize" the numbers by changing units nor using extraneous
"significant" digits.
They called the 506 a "5 Megabyte drive", NOT "5.33" nor
"5.08".
They called the 412 a "10 Megabyte drive", NOT "10.4" nor
"10.16".
I believe the last 2 digits of those model numbers was the unformatted capacity in some
flavour of megabytes. As well as the ST412 (which had 2 platters, 4 heads), there
were the less common ST406 (one platter, 2 heads) and ST419 (3 platters, 6 heads).
I guess it was a bit over 6 megabyes per platter, so by the time you had 3 of them
it rounded to 19 megabytes unformatted.
The ST406 and ST419 were used in the HP9133V and 9133XV respectively where the
suffix letters helpfully give the formatted capacity in roman numerals.
-tony
1:17 p.m.
NOTE: In
contrast with modern marketing, Seagate did NOT try to
"maximize" the
numbers by changing units nor using extraneous
"significant" digits.
They called the 506 a "5 Megabyte drive", NOT "5.33" nor
"5.08".
They called the 412 a "10 Megabyte drive", NOT "10.4" nor
"10.16". I believe the last 2 digits of those model numbers was
the unformatted
capacity in some flavour of megabytes. As well as the ST412 (which had 2
platters, 4 heads), there were the less common ST406 (one platter, 2
heads) and ST419 (3 platters, 6 heads). I guess it was a bit over 6
megabyes per platter, so by the time you had 3 of them it rounded to 19
megabytes unformatted. The ST406 and ST419 were used in the HP9133V and
9133XV respectively where the suffix letters helpfully give the
formatted capacity in roman numerals.
Seagate was generally very good about providing the unformatted capacity,
as well as the formatted capacity ROUNDED DOWN. They were even
cooperative about publishing the drive geometry.
Even unformatted capacity is potentially ambiguous. In addition to the
basic geometry (number of heads and cylinders), it can further depend on
the spindle speed (function of the drive) the data transfer rate (function
of the controller), and encoding (function of the controller).
NEC, for instance ran their 3.5"HD disk at 360RPM, when almost everybody
else was using 300 RPM.
For floppies, there was encoding of FM, MFM, GCR, and a few others.
For a while, there were "RLL hard drives", which could be used as MFM with
good reliability, but corresponding lower capacity. And there were
always a few power lusers who would attempt to use MFM drives as RLL, and
declare them "perfectly usable" if there were not immediate failures
(much like Spinrite restoring to use sectors that had been demonstrated to
be unreliable, if they passed one test).
Comparing drive capacities reliably required either knowing ALL of the
parameters, or making assumptions of some of them.
--
Grumpy Ol' Fred cisin at xenosoft.com
2:36 p.m.
For one terabyte, the difference is close to 10
gigabytes...
(For one meg, the difference is 48K).
The rough-approximation estimates I usually use are 2.5%, 5%, 7%, 10%
for K, M, G, T. (The precise values depend on whether you're talking
about the amount by which the metric values fall short of the binary
values or the amount by which the binary values exceed the metric
values. But even for TB that's 9.95+% vs 9.05+%, not a huge
difference.)
> Actually, the notes in the ads were added later
due to litigious
> bastards and other chancers claiming that they believed it to mean
> powers-of-two and making a nuisance of themselves in court.
Such a claim would not have been plausible enough to get anything but a
summary judgement for the defendant, with costs, if there hadn't, at
the time, been well-established power-of-two meanings.
And at least one manufacturer outright lied to me about it. Back when
Zip disks came out, they were sold as 100MB. They were actually 96MB
(bang on the nose, too - 196608 sectors, not 96.026+MB or any such). I
had occasion to call iOmega for something else related to Zip disks and
asked them where the other 4MB went, not because I didn't know but
because I was curious what they'd say.
They told me the 100MB was unformatted capacity. Even then, 4%
formatting overhead seemed unrealistically low to me, and a techie who
once worked for them and knew the low-level details later confirmed to
me that the formatting overhead was more like 20 to 30 percent.
I didn't call them on it; I couldn't see any good result from doing
that. But that they had the lie prepared and had primed their
front-line phone people with it made it clear to me that (a) it _was_ a
lie and (b) they knew the truth would not go over well.
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3:35 p.m.
On 12/06/2014 02:36 PM, Mouse wrote:
And at least one manufacturer outright lied to me about it. Back when
Zip disks came out, they were sold as 100MB. They were actually 96MB
(bang on the nose, too - 196608 sectors, not 96.026+MB or any such). I
had occasion to call iOmega for something else related to Zip disks and
asked them where the other 4MB went, not because I didn't know but
because I was curious what they'd say.
I dunno--if you go by the 1MB = 10**6 bytes, it's pretty accurate for
both the 100 (100663296 bytes) and the 250 (250640384 bytes).
Reminds me of the old Python sketch about "Anything Goes"...
--Chuck
6:02 p.m.
> Back when Zip disks came out, they were sold as
100MB. They were
> actually 96MB [...]. I had occasion to call iOmega for something
> else related to Zip disks and asked them where the other 4MB went,
> not because I didn't know but because I was curious what they'd say.
I dunno--if you go by the 1MB = 10**6 bytes, it's
pretty accurate
[...]
Well, yes; I knew that was "where the 4MB went". I was curious whether
they would try to "correct" the 96M figure or what...and it turned out
to be "what".
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5 Dec
5 Dec
9:24 p.m.
On Sat, 6 Dec 2014, Johnny Billquist wrote:
. . .
While you have a half point, Mouse, the fact is that for disk
capacities, the standard is actually to use K to mean 10^3 and not 2^10,
so Fred is absolutely right.
How dare you!?! :-)
I was not the one who said it, and I haven't been absolutely right about
anything in a long time.
--
Grumpy Ol' Fred cisin at xenosoft.com
6 Dec
6 Dec
3:33 a.m.
On 2014-12-06 06:24, Fred Cisin wrote:
On Sat, 6 Dec 2014, Johnny Billquist wrote:
:-)
My mistake. It was Eric. I'll try to remember not attributing anything
absolutely right to you in the future. :-)
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
. . .
While you have a half point, Mouse, the fact is that for disk
capacities, the standard is actually to use K to mean 10^3 and not 2^10,
so Fred is absolutely right.
How dare you!?! :-)
I was not the one who said it, and I haven't been absolutely right about
anything in a long time. 
5 Dec
5 Dec
8:29 p.m.
It was thus said that the Great Peter Corlett once stated:
On Fri, Dec 05, 2014 at 06:05:20PM -0500, Jerome H.
Fine wrote:
[...]
I started with computers in the 80s, and back then, I learned the
following:
1K = 2^10
1M = 2^20
1G = 2^30
So that 64K (address space of your typical 8-bit CPU) gave you 65,536 bytes
and 16M (a popular 32-bit CPU at the time came with a 24-bit address space,
as well as a popular upgraded 16-bit CPU) gave you 16,777,216 bytes and no
amount of whining will ever convince me it's 65K and 16.7M of memory.
-spc (Why yes, computers are special little snowflakes entitled to be
different ... )
Assuming that 1 terabyte is 2 ** 40 bytes [...]
It's not, it's 10**12. Every other use of SI multipliers are powers-of-ten,
and computers are not special little snowflakes entitled to be different. 
10:46 a.m.
The trivia question is:
Approximately how many DECtapes will fit on a single one terabyte drive?
I should think that you are unlikely to be able to stack more than 20 or so without the
pile falling-off. 
2:37 p.m.
On 12/5/2014 9:59 AM, Doug Ingraham wrote:
I have had my PDP-8 (no letter) since around 1985. As
part of the deal I
got a little over 200 DECtapes. Most of these are SCOTCH 3M branded in
cardboard boxes and not DEC branded DECtapes in the clear blue plastic
containers. I have been thinking about moving this data to a permanent
storage location so I wondered how much space this would require. Turns
out to be about 57 million bytes and that would be without bothering to do
any compression.
The trivia question is:
Approximately how many DECtapes will fit on a single one terabyte drive?
As there are several possible answers to this feel free to reply on the
list. I will give my answer in a few days.
*ONE*, placed nicely over the top of the HD.
Doug Ingraham
Ben.
2:44 p.m.
On 12/5/2014 3:37 PM, ben wrote:
On 12/5/2014 9:59 AM, Doug Ingraham wrote:
No wait. *NONE* if that is a empty reel. :)
Ben.
I have had my PDP-8 (no letter) since around
1985. As part of the deal I
got a little over 200 DECtapes. Most of these are SCOTCH 3M branded in
cardboard boxes and not DEC branded DECtapes in the clear blue plastic
containers. I have been thinking about moving this data to a permanent
storage location so I wondered how much space this would require. Turns
out to be about 57 million bytes and that would be without bothering
to do
any compression.
The trivia question is:
Approximately how many DECtapes will fit on a single one terabyte drive?
As there are several possible answers to this feel free to reply on the
list. I will give my answer in a few days.
*ONE*, placed nicely over the top of the HD.
Doug Ingraham
Ben.
9 Dec
9 Dec
8:38 a.m.
Oh my! I never expected to kindle a flame war (maybe it is rekindle).
My favorite answer is "All of them." If you assume a terrabyte is
1000000000000 bytes which is 10^12 and the smallest you could expect such a
drive to be. And also assume a DECtape (not DECtape II) has an unformatted
capacity of 2700000 bits which is 337500 bytes. So smallest drive capacity
and largest DECtape capacity would give at least 2962962 DECtapes. Larger
drives and smaller capacity tapes only increase this value. We know that
DECtapes used by OS/8 have usable capacity of 283008 bytes. In that case
it would be 3533469 tapes. It is unlikely that even 2.9 million tapes
were manufactured.
As for physically stacking tapes on a drive, I suppose you could rig up a
platform that could hold tapes up to the point where the drive was
crushed. I would weigh a reel if I was writing this at home. I will
estimate a reel weighs 4 ounces. That means the 2.9 million tapes would
weigh 725000 lbs or 362 tons.
A reel has 260 ft of tape so to wrap around the earth at the equator would
only require 505682 tapes.
I will see if my next trivia question can avoid a minor flame fest even
though they are fun to watch from time to time.
Doug Ingraham
On Fri, Dec 5, 2014 at 9:59 AM, Doug Ingraham <dpi at dustyoldcomputers.com>
wrote:
I have had my PDP-8 (no letter) since around 1985. As
part of the deal I
got a little over 200 DECtapes. Most of these are SCOTCH 3M branded in
cardboard boxes and not DEC branded DECtapes in the clear blue plastic
containers. I have been thinking about moving this data to a permanent
storage location so I wondered how much space this would require. Turns
out to be about 57 million bytes and that would be without bothering to do
any compression.
The trivia question is:
Approximately how many DECtapes will fit on a single one terabyte drive?
As there are several possible answers to this feel free to reply on the
list. I will give my answer in a few days.
Doug Ingraham
12:01 p.m.
Doug Ingraham wrote:
Oh my! I never expected to kindle a flame war (maybe
it is rekindle).
My favorite answer is "All of them." If you assume a terrabyte is
AGREED! However, you should really obtain some production figures
to justify that conclusion.
1000000000000 bytes which is 10^12 and the smallest you
could expect such a
drive to be. And also assume a DECtape (not DECtape II) has an unformatted
capacity of 2700000 bits which is 337500 bytes. So smallest drive capacity
I contend that the unformatted capacity of 337500 is completely
irrelevant since even if the unformatted capacity had been 10 times
that value, it would have made no difference in the number of bytes
written to the hard drive. After all, the system reading the DECtape
received only the formatted result into memory (the hardware in the
controller probably did the reduction). The same information would
then be written to the hard drive irrespective of the efficiency of the
method used to allow for errors when the DECtape was read and
the extra bytes in each sector or block were used to detect if an
error was present.
and largest DECtape capacity would give at least
2962962 DECtapes. Larger
drives and smaller capacity tapes only increase this value. We know that
DECtapes used by OS/8 have usable capacity of 283008 bytes. In that case
it would be 3533469 tapes. It is unlikely that even 2.9 million tapes
were manufactured.
The number of DECtapes which were manufactured is really the
essential aspect of your (trick?) question. I do agree that since
only a DEC user would have ever used a DECtape, less than
2.9 million tapes were ever made. Can anyone who worked
at DEC confirm this?
I do apologize for starting the flame war when I provided my
description of the number of bytes in a terabyte, but that was
only to have a simple formula for the number of tapes whose
read contents (not the unformatted sectors) could be written
onto the hard drive.
Jerome Fine
10 Dec
10 Dec
11:28 a.m.
As for physically stacking tapes on a drive, I suppose you could rig up a
platform that could hold tapes up to the point where the drive was
crushed. I would weigh a reel if I was writing this at home. I will
estimate a reel weighs 4 ounces. That means the 2.9 million tapes would
weigh 725000 lbs or 362 tons.
Today while unpacking some more stuff after the move I found the pan from my
grandmother's kitchen scales (it was packed in with books and cables, go figure..)
Anyway that meant I could weigh a DECtape. The reel in the plastic case weights about
6.75 ounces, the reel on its own (with the tape on it, of course) weighs about 3.8
ounces.
So your guess was pretty good. Certainly near enough for this
Said scales are of the sliding weight type so there are no springs that could have gone
soft over the years. Yes, corrosion probably has affected the weights a bit, but not
enough
to worry about.
-tony
3664
days inactive
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43 comments
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