Wikipedia - User contributions [en]

Amazon S3 Glacier

2018-02-01T21:15:57Z

EmptyString: /* Cost */

{{ infobox website
| name = Amazon Glacier
| logo =| logocaption =
| type = [[Remote backup service|Online backup service]]
| language = [[English language|English]]
| current status = Active
| url = {{url|http://aws.amazon.com/glacier/}}
| ipv6 =
| commercial = Yes
| registration = Required
| owner = [[Amazon.com]]
| launch date = August 21, 2012<ref>{{cite web |url=https://aws.amazon.com/blogs/aws/amazon-glacier-offsite-archival-storage-for-one-penny-per-gb-per-month/ |title=Amazon Glacier: Archival Storage for One Penny Per GB Per Month |publisher=AWS Blog |accessdate=November 29, 2016 |author=Jeff Barr |date=August 21, 2012}}</ref>
}}

'''Amazon Glacier''' is an [[online file storage]] [[web service]] that provides storage for data archiving and backup.<ref>{{cite news | first = Stephanie | last = Mlot | title = Amazon Launches Glacier Cloud Storage Service | date = August 21, 2012 | url= https://www.pcmag.com/article2/0,2817,2408707,00.asp | publisher = Ziff Davis, Inc. | work = PCMag.com | accessdate = 2012-08-21}}</ref>

Glacier is part of the [[Amazon Web Services]] suite of cloud computing services, and is designed for long-term storage of data that is infrequently accessed and for which retrieval latency times of 3 to 5 hours are acceptable. Storage costs are a consistent $0.004 per gigabyte per month, which is substantially cheaper than Amazon's own [[Amazon S3|Simple Storage Service (S3)]].<ref>{{cite web|url=https://aws.amazon.com/s3/pricing/ |title=Pricing |publisher=Aws.amazon.com |date= |accessdate=2015-06-18}}</ref>

Amazon hopes this new service will move businesses from on-premises [[Tape drive|tape backup drives]] to [[Storage as a service|cloud-based backup storage]].<ref name="zdnet7000002926">{{cite news | first = Jack | last = Clark | title = Amazon launches Glacier cloud storage, hopes enterprise will go cold on tape use | date = August 21, 2012 | publisher = CBS Interactive | work = ZDNet | url= http://www.zdnet.com/amazon-launches-glacier-cloud-storage-hopes-enterprise-will-go-cold-on-tape-use-7000002926/| accessdate = 2012-08-21}}</ref>

==Storage==
ZDNet says, that according to private e-mail, Glacier runs on "inexpensive commodity hardware components".<ref name="zdnet7000002926"/> In 2012, [[ZDNet]] quoted a former Amazon employee as saying that Glacier is based on custom low-RPM hard drives attached to custom logic boards where only a percentage of a rack's drives can be spun at full speed at any one time.<ref name="zd7000003144">{{cite web|last=Clark |first=Jack |url=http://www.zdnet.com/could-the-tech-beneath-amazons-glacier-revolutionise-data-storage-7000003144/ |title=Could the tech beneath Amazon's Glacier revolutionise data storage? |publisher=ZDNet |date=2012-08-24 |accessdate=2015-06-18}}</ref><ref>{{cite web|url=https://news.ycombinator.com/item?id=4416065 |title=Former S3 employee here. I was on my way out of the company just after the stora... | Hacker News |publisher=News.ycombinator.com |date= |accessdate=2015-06-18}}</ref> (Similar technology is also used by [[Facebook]].)<ref>https://arstechnica.com/information-technology/2015/11/to-go-green-facebook-puts-petabytes-of-cat-pics-on-ice-and-likes-windfarming/</ref>

There is some belief amongst users that the underlying hardware used for Glacier storage is tape-based, owing to the fact that Amazon has positioned Glacier as a direct competitor to tape backup services (both on-premises and cloud-based).<ref>{{cite web|url=http://www.extremetech.com/computing/134776-amazon-glacier-99-999999999-durability-long-term-storage-for-a-penny-a-gig |title=Amazon Glacier: 99.999999999% durability long-term storage, for a penny a gig |publisher=ExtremeTech |date=2012-08-21 |accessdate=2015-06-18}}</ref> This confusion is exacerbated by the fact that Glacier has archive retrieval delays (3–5 hours before archives are available) similar to that of tape-based systems and a pricing model that discourages frequent data retrieval.<ref>{{Cite web|title=One of tech’s most elusive mysteries: The secret of Amazon Glacier|date=9 November 2013|author=Paul Cooper|website=IT ProPortal|url=http://www.itproportal.com/2013/11/09/one-of-techs-most-elusive-mysteries-the-secret-of-amazon-glacier/}}</ref>

''[[The Register]]'' claimed that Glacier runs on [[Spectra Logic|Spectra T-Finity]] tape libraries with [[LTO-6]] tapes.<ref>{{cite web|url=https://www.theregister.co.uk/2012/10/18/ipexpo_2012/ |title=Insider 'fesses up: Amazon's Glacier cloud is made of ... TAPE |publisher=Theregister.co.uk |accessdate=2015-06-18}}</ref><ref>{{cite web|url=https://www.theregister.co.uk/2013/02/28/spectra_h1_fy2013/ |title=Spectra: Tape is dead? We installed 550PB of the stuff in 6 months |publisher=Theregister.co.uk |accessdate=2015-06-18}}</ref> Others have conjectured Amazon using off-line [[shingled magnetic recording]] hard drives, multi-layer [[Blu-ray]] [[optical disc]]s, or an alternative proprietary storage technology.<ref>{{cite web|url=http://storagemojo.com/2014/04/25/amazons-glacier-secret-bdxl/ |title=Amazon’s Glacier secret: BDXL |publisher=Storagemojo.com |date= |accessdate=2015-06-18}}</ref>

==Cost==
Glacier has two costs, one for storage and one for retrieval. Uploading data to Glacier is free. Storage pricing is simple: it currently costs 0.4 cents per gigabyte per month, which is 82% cheaper than S3 Standard.

Glacier used to charge for retrievals based on ''peak'' monthly retrieval rate, meaning that (ignoring the free tier) if you downloaded four gigabytes in four hours, it would cost the same as if you downloaded 720 gigabytes in 720 hours, in a 30-day month. This made it cheaper to spread out data retrievals over a long period of time, but failing to do so could result in a surprisingly large bill. In one case, a user stored 15 GB of data in Glacier, retrieved 693 MB for testing, and ended up being charged for 126 GB due to retrieval rate calculation.<ref>{{cite web |url=https://forums.aws.amazon.com/message.jspa?messageID=383204 |date=21 September 2012 |title=FastGlacier surprising Retrieval Fee |work=AWS Developer Forums |publisher=Aws.amazon.com |accessdate=30 January 2013 }}</ref> This pricing policy was widely regarded as a “time bomb” set to go off on retrieval.<ref>https://www.wired.com/2012/08/glacier/</ref>

In 2016, AWS revised their retrieval pricing model.<ref>{{cite web|url=https://aws.amazon.com/blogs/aws/aws-storage-update-s3-glacier-price-reductions |title=AWS Storage Update – S3 & Glacier Price Reductions + Additional Retrieval Options for Glacier|publisher=aws.amazon.com|date=2016-11-21|accessdate=2018-02-01}}</ref> The new model bases the retrieval fee on the number of gigabytes retrieved. This can amount to a 99% price cut for users who perform only one glacier retrieval in a month. At the same time, AWS introduced new methods of retrieval that take different amounts of time. An ''expedited'' retrieval costs one cent per request and three cents per gigabyte, and can retrieve data in one to five minutes. A ''standard'' retrieval costs five cents per thousand requests and one cent per gigabyte, and takes three to five hours. A ''bulk'' retrieval costs 2.5 cents per thousand requests and 0.25 cents per gigabyte, and takes seven to twelve hours. AWS also introduced ''provisioned capacity'' for expedited retrievals, each unit of which costs $100 per month and guarantees at least three expedited retrievals every five minutes, and up to 150 MB/s of retrieval bandwidth. Without provisioned capacity, expedited retrievals are done on a capacity available basis.<ref>{{cite web|url=https://aws.amazon.com/glacier/faqs/#dataretrievals |title=Glacier FAQ: Data Retrievals|publisher=aws.amazon.com|accessdate=2018-02-01}}</ref>

Data deleted from Glacier less than 90 days after being stored incurs a charge equal to the cost of storage for the remainder of the 90 days. (In effect, the user pays for 90 days minimum.) This move was designed to discourage the service's use in cases where Amazon's other storage offerings (e.g. [[Amazon S3|S3]]) are more appropriate for real-time access. After 90 days, deletion from Glacier is free.

Retrieving data from Glacier is a two-step process. The first step is to retrieve the data into a staging area, where it stays for 24 hours.<ref>{{cite web|url=https://docs.aws.amazon.com/amazonglacier/latest/dev/downloading-an-archive-two-steps.html|title=Retrieving Amazon Glacier Archives|publisher=aws.amazon.com|accessdate=2018-02-01}}</ref> The second step is to download the data from the staging area, which may incur bandwidth charges.<ref>{{cite web|url=https://aws.amazon.com/glacier/pricing/|title=Amazon Glacier Pricing|publisher=aws.amazon.com|accessdate=2018-02-01}}</ref>

Glacier is also available as a “storage class” in S3.<ref>{{cite web|url=https://aws.amazon.com/s3/storage-classes/|title=Amazon S3 Storage Classes|publisher=aws.amazon.com|accessdate=2018-02-01}}</ref> Objects can only be put into Glacier by lifecycle rules, which can be configured to put the objects in Glacier once they have reached a certain age. Pricing is the same, but there is no staging area; instead, retrieved objects are simultaneously stored in Glacier and in Reduced Redundancy class for a number of days that the user specifies.

==References==
{{Reflist|30em}}

== External links ==

* {{official website|http://aws.amazon.com/glacier/}}

{{Cloud computing}}
{{Amazon}}

[[Category:Cloud storage]]
[[Category:Amazon Web Services|Glacier]]

Simplified Instructional Computer

2012-05-07T17:03:14Z

EmptyString:

{{Unreferenced stub|auto=yes|date=December 2009}}
{{Orphan|date=February 2009}}

The '''Simplified Instructional Computer''' (also abbreviated SIC) is a hypothetical [[computer]], that is used as a base to explain the operation of a real computer. It was stated that most real microprocessors have a complex instruction set and many subtleties to increase efficiency, that can be a distraction for students that are studying the essential and universal aspects of a [[microprocessor]] (that are common to different designs). Hence this hypothetical computer is used to explain all the basic concepts of microprocessor design even though it is impossible to cover every aspect. The architecture of the SIC uses 3 byte integers, 5 registers and can access 2<sup>15</sub>=32768 bytes of memory.

==The five registers==
* '''A''' register (accumulator): This is the three-byte register that is used for arithmetic operations.
* '''X''' register (index): The index register can operate in two modes, direct and indexed.
* '''SW''' register (status word)
* '''PC''' register (program counter)it contains the address of next instruction to be fetched for execution.
* '''L''' register (linkage): This register is used for subroutine jumps.

Integer values are stored in 2's complement format.The ASCII encoding scheme is used for characters. The SIC has two versions; a standard version SIC, and an extended version SIC/XE. The extended version has floating point numbers.

==See also==
* [[Computer]]
* [[MIX]]
* [[System software]]
* [[Assembly language]]
* [[Processor register]]
* [[Virtual machine]]

== References ==

{{reflist}}
* {{Citation |last=Beck |first=Leland |authorlink=Leland L. Beck |title=System Software: An Introduction to Systems Programming |year=1996 |edition=3 |publisher=Addison-Wesley |isbn=0-201-42300-6}}

==External links==
* [http://sourceforge.net/projects/sicvm/ SICvm] A Virtual Machine based on a Simplified Instructional Computer (SIC)

[[Category:Educational abstract machines]]

{{Compsci-stub}}

[[zh:簡化指令計算機]]

Talk:Spaghettification

2007-04-19T22:54:52Z

EmptyString: Another kind of spaghettification?

{{physics|class=|importance=}}
([[User:William M. Connolley|William M. Connolley]] 17:33, 5 Sep 2004 (UTC)) This page might benefit from a link to [[:Image:Tidal-forces-calculated.png]].

Who's got a picture of an astronaut being spaghettified?? [[User:204.52.215.99|204.52.215.99]] 15:12, 28 March 2007 (UTC)

I'm sorry about making seemingly irrational changes and saying it was not needed; in my browser there has recently been a change meaning that the images are placed neatly below each other at all times. I thought this was a welcomed new wikipeida feature. [[User:Sverdrup|<span style=" font-family: Optima, sans-serif; border-bottom: 1px solid blue;">[[User:Sverdrup|❝'''S'''verdrup❞]]</span>]] 20:14, 6 Sep 2004 (UTC)

:They line up neatly for me too. Perhaps it's a browser issue?(firefox 0.9.3). Mind you even if it is, it's clearly better to go with Bryan so that it looks good for everyone. [[User:Theresa knott|Theresa Knott]] [[User talk:Theresa knott| (Nate the Stork)]] 20:25, 6 Sep 2004 (UTC)

:Ah, I see. I'm using Mozilla 1.8a1 with the "Classic" Wikipedia skin, if you're curious. I would also welcome a new Wikipedia feature like that. :) [[User:Bryan Derksen|Bryan]] 20:27, 6 Sep 2004 (UTC)

==Sure of it?==

'' Eventually, close to the singularity, they become large enough to tear atoms apart.'' -Anon

:You make a good point. No come to think of it I'm not sure. I've reworded the text. [[User:Theresa knott|Theresa Knott]] [[User talk:Theresa knott| (The torn steak)]] 12:26, 17 Oct 2004 (UTC)

==Accelerated Towards?==

Gravity is fixed acceleration.
Even going down a black holes throat.
The space/frames of refrence are going to elongate,
and light is going to slow down to the outside observe.

but the acceleration due to gravity is the same.
Due to the acceleration, your velocity increases,
and due to the velocity increase, as you go faster,
your distance down the hole increases.

This is all that happened when the Apple fell from the tree.

Which theory of gravity are you working with?

[[User:Artoftransformation|Artoftransformation]] 17:15, 9 November 2005 (UTC)

I spent a while pondering your comment, trying to think of a way to ask exactly what you're talking about without sounding patronizing. I couldn't think of one, sorry. What are you talking about, specifically?

This doesn't have to bring in time dilation or relativistic velocity or anything silly at all, this is basic physics alone. Of course at any specific distance, gravitational acceleration is fixed, but that's really the entire point. You don't usually notice tidal forces (our ocean being an obvious exception), this is just an extreme case since black holes are relatively small so the differences in acceleration are magnified, and relatively huge stuff gets sucked into them.

Example: Pick up a ball bearing and drop it, it falls at ~9.8m/s^2 because you're standing around 6000km away from the center of the Earth. Get a really tall ladder and drop another ball bearing from 3000km above the surface of the earth, and it only falls at 4.9m/s^2. Now, take a 3000km-long foam noodle, hold it by one end so the bottom end is a few hundred meters above the Earth's surface, and drop it. Ignoring air resistance, what happens? After the first second, the bottom end has fallen 4.9 meters, while the top end has fallen 2.45; it stretches out to compensate for this difference. Earth's gravity might not even be sufficiently strong for the sake of this example - pretend there's a big metal ball at both the top and bottom ends, whatever. The point is that with black holes, you don't need to use foam rubber; their high mass/density by definition means that there's going to be enough free space to fall in for the tidal forces to become strong enough to rip nearly anything apart (ie. tidal force drops off much faster than gravitational force, and we start running into dirt and stuff by the time we get within 6000km or so of the center of the Earth's mass).

Just as a totally trivial, but at least possible, example (physics is not my forte), take a black hole of a thousand solar masses. Its Schwarzschild radius is 2952m, so pretend we're somehow hovering (100000m-2952m) above it, and that we're 2m tall. Get out of your still-hovering spaceship and fall. Yeah, it'll only take you 1.226x10^-4 sec to splatter, but in that time, based '''only''' on the '''original''' disparity in acceleration due to the difference in distance of your head and feet, your head will have fallen 4m less than your feet. Of course this also assumes you're basically a person-shaped pile of dust, but with this sort of force (stretching 4 meters in 100 microseconds), I don't imagine the human body would put up much resistance at all. In reality you'd be stretched much farther, due both to your height becoming more relatively significant compared to the decreasing distance, and your absolute height increasing the entire time you fell.

The second component of spaghettification has nothing to do with tidal force per se - like the article's top diagram shows, if you have something that is wide (not difficult when you drop a star into a black hole that's a few km across), its edges will be pushed together, moreso at the bottom, because their definition of "down" is different. I don't know if this would normally work fast enough to push the top and bottom apart from each other, but it'd at least make the object thinner. [[User:Straker|Straker]] 11:39, 11 November 2005 (UTC)

Whoops. Okay, so my quick example obviously entails going FTL. Sillily enough, this doesn't break anything in the concept of spaghettification itself, so if this happens to bother you, play with the numbers some (a thousand solar masses is kind of a weird mass anyways, should usually be much heavier or much lighter). [[User:Straker|Straker]] 12:10, 12 November 2005 (UTC)

==Can't spaghettification be explained much more simply?==
It looks to me like this article is overcomplicated and spaghettification
can be explained in under 30 lines, plus possibly 1 very simple diagram (using Newtonian gravity):
* Gravitational pull is inversely proportional to the square of distance.
* So the pull on the near side of an object is greater than the pull on the far side.
* That means the near side wants to accelerate faster than the far side towards the source of the gravity field.
* This difference in acceleration creates tension between the 2 sides of the object. The tension is proportional to 2 factors: the length of the object in the direction pointing towards the gravity source; the strength of the gravitational force.
*For "normal" gravity fields, like Earth's, the effect is negligible if the object is smaller than a large asteroid. But in an extremely strong gravity fields, such as a black hole's, the tension can become enough to stretch the object and eventually pull it apart.
* Spaghettification contains a positive feedback loop - as the "victim" gets longer, the tensile force increases, etc.
* If the gravity source is very small (e.g. black hole) and the "victim" is relatively large, the stretching is increased by lateral compression since the sides of the "victim" are falling along converging paths. If the lateral compression actually increases the "victim's" length, it also increases the tensile force, etc.
Or am I missing something?

If I'm right and the article can be simplified, we can use the extra space for additional aspects, e.g.: any new features added by general relativity; spahettification eventually destroys atoms and even sub-atomic particles falling into black holes, because as the distance from the black hole decreases the gravitational pull increases very fast (inverse square law) and the difference in distance between the leading and trailing edges of the "victim" becomes a large fraction of the distance to the black hole; what happens when 2 black holes meet.[[User:Philcha|Philcha]] 18:55, 16 March 2007 (UTC)

==Does the "tidal forces" diagram help non-specialist readers?==
I doubt whether the diagram "tidal forces acting on a spherical body in a gravitational field" helps non-specialist readers. To understand it I think readers would need to understand (a) the basic principles of tidal forces; (b) how to split forces into components and re-combine them; (c) the convention that length of arrow is proportional to strength of force.[[User:Philcha|Philcha]] 13:30, 28 March 2007 (UTC)

==Should the article mention another kind of spaghettification?==

The process where a [[computer program]] turns to [[spaghetti code]]. Interestingly enough, it is also an indication that the program is falling into a [[black hole]]. (It didn't look like there was an appropriate place to mention this in the article though.)

Parent pointer tree

2007-04-06T23:40:44Z

EmptyString:

A '''spaghetti stack''' (also called a '''cactus stack''') is an N-ary [[tree data structure]] in which [[child node]]s have pointers to the [[parent node]]s. When a list of nodes is traversed from a leaf node to the [[root node]] by chasing these parent [[pointer]]s, the structure looks like a [[linked list]] [[stack (data structure)|stack]]. You can just pretend that the one and only parent pointer is called "next" or "link", and ignore that the parents have other children, which are not accessible anyway since there are no downward pointers.

Spaghetti stack structures arise in situations when records are dynamically pushed and popped onto a stack as execution progresses, but references to the popped records remain in use.

For example, a [[compiler]] for a language such as [[C (programming language)|C]] creates a spaghetti stack as it opens and closes [[symbol table]]s representing block scopes. When a new block scope is opened, a symbol table is pushed onto a stack. When the closing curling brace is encountered, the scope is closed and the symbol table is popped. But that symbol table is remembered, rather than destroyed. And of course it remembers its higher level "parent" symbol table and so on. Thus when the compiler is later performing translations over the abstract syntax tree, for any given expression, it can fetch the symbol table representing that expression's environment and can resolve references to identifiers. If the expression refers to a variable X, it is first sought after in the leaf symbol table representing the inner-most lexical scope, then in the parent and so on.

The term spaghetti stack is closely associated with implementations of programming languages that support [[continuation]]s. Spaghetti stacks are used to implement the actual [[run-time stack]] containing variable bindings and other environmental features. When continuations must be supported, a function's local variables cannot be destroyed when that function returns: a saved continuation may later re-enter into that function, and will expect not only the variables there to be intact, but it will also expect the entire stack to be there, so it can return again! To resolve this problem, [[stack frame]]s can be [[dynamic memory allocation|dynamically allocated]] in a spaghetti stack structure, and simply left behind to be [[garbage collection (computer science)|garbage collected]] when no continuations refer to them any longer. This type of structure also solves both the upward and downward [[funarg problem]]s, so first-class lexical [[closure (computer science)|closure]]s are readily implemented in that substrate also.

The [[Felix programming language]] uses a spaghetti stack implemented with ISO [[C++]] classes as its primary execution model. Its key feature, high performance user space [[thread (computer science)|threading]], relies on this model, by allowing an unlimited number of threads of control to be active, each having its own local spaghetti sub-stack, but sharing the base of its creator.

==References==
{{Unreferenced|date=January 2007}}

[[Category:Data structures]]

Cactus stack

2007-04-06T23:40:20Z

EmptyString: ←Redirected page to Spaghetti stack

#Redirect [[Spaghetti stack]]