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Disk Drives Explained
CowboyRobot writes "Magnetic disk drives are one of those things I usually take for granted without thinking about, but I recently realized how little I understood about how they really work. ACM Queue has an article from their 'Storage' issue titled, 'You Don't Know Jack About Disks', which does a very good job of explaining exactly how magnetic disks have evolved since the 70s and how they work today."
That's simple; "What computer were you planning on buying?"
I don't know your experience, though this is mine;
I've put computers together for people, I've given them advice, I've even given them a store plus model name plus a few suggestions. I've warned people off of buying a brand, and told them that there are problems with specific hardware that they have thier eye on. All good stuff...none of it aimed toward an agenda...all focusing on what they said they want to do with a specific budget...and they always end up buying what they wanted in the first place or (if I put it together) drooling over the machine they really wanted.
There is no other answer. Unfortunately, the same thing often applies in business though if the managers have good computers they tend to ignore what you do with the rest of the systems.
A firewall can not protect you from yourself. Turn off what you do not need. Do not use the firewall to do your work.
If someone asks me which computer to buy, I'd like to think I could assess their level of technical understanding and their needs in under two hours, provide encouragement, explanation, and make a useful recommendation. Your attitude alienates people.
It always intresting to see how things work. Nice little thing to add to this is the way Nintendo do copy protection on their disks (although not scritly on topic). Instead of relying on heavy software encryption they went for a nice simple solution. They spin the CD-Rom the wrong way. As such you need special burners if you want to copy it.
Now thats a neat idea
Rus
Cheap UK and US VPS
"Fatal error: Call to undefined function: message_die() in db/db.php on line 88"
So... anybody got a mirror?
fsck -u
To take the IBM mainframe example he quotes: yes, IBM originally used a CKD (count-key-data) architecture and this was still preferred in the late 1970s for highest performance applications. However, in the last 1970s, IBM already provided FBA (fixed block architecture) disk drives such as the 3370. These moved intelligence of disk geometry into the disk controller and were quite easy to program.
Other mainframe and minicomputer manufacturers had innovative schemes during the early 1980s.
I don't know about you, but 99.9% of the the time the people that ask me about a computer:
a) have no clue about the difference between hard drive space and RAM memory.
b) "just want to get online", but have no clue what that really means.
I've set a few people up with old PII/350's, just to get them a computer in the first place... it gets them online and they can browse the web, email, etc. I tell them, rather than spend $1000 today to buy a machine, spend it next year and use the 350 to get a clue about what it is you want.
It works. Generally they buy some game that won't run well on less than an 833 or something, and while they still don't know what the difference between a "megahertz" and a "gigahertz" (and no, trying to explain the metric system to them doesn't work), they at least have a better idea of what a computer *is* and what they want to do with it.
*Then* I make a recommendation on what they need based on what they want to do with it.
Furthermore the rare element production takes often place in very anarchic countries like Kongo or Liberia. Usually warlords and local terrorists use the money from the disk drives rare elements to finance their blood raids and terrorship.
That's btw the reason why the US were setting up Kabila in Kongo. This guy was killed, but only because the French were more clever.
So, instead of this old technology which is going to be phased out in 5 years anyway, you should use more modern flash/ram disks and DVDs for data storage, just for moralic reasons.
Think about it: If you refuse to buy bananas or big name brands because of the cruel, inhumane exploitation of the third-world workers, then you should do the same in IT and avoid disk drives.
Owner of a Mensa membership card.
There are probably lots of articles on the subject that can be bought up with a quick search, but my favourite broad explanation site has their definition here.
Well, there's an interesting article about hard drives here. Watch out, though, it's quite long and it's an easy way to waste some hours... But sure you wanted to know why we don't need to park the hard disk's heads anymore? =) Or, that in fact, there are holes in the hard drive, so it can "breathe".
On page 6 (ATA versus SCSI) Mr. Anderson (insert matrix joke here) references "ATA versus SCSI: More Than an Interface," by Dave Anderson, Erik Riedel, and Jim Dykes.
The pdf can he had here: ATA_vs_SCSI
I thought it was quite an interesting read, and an excellent companion piece to the "You Don't Know Jack about Disks" article.
RFC2119
Unfortunately, we're still quite a ways from developing solid-state drives cheaply that can finally compete against today's hard drives.
:-)
I think within the next 15 years we will finally see the breakthrough that will essentially turn our primary storage into physically-removeable cartridges of solid-state non-volatile memory storing over 250 GB of data on a cartridge somewhat smaller than the physical dimensions of a 3.5" floppy drive. And unlike today's non-volatile memory, the new solid-state memory can be erased many trillions of times without affecting the life of the memory.
The big advantage of solid-state storage is that since the delay in reading and writing data is a tiny fraction of that of hard drives, they could access data at extraordinarily fast speeds. Imagine loading something like Windows 2000 Professional in under two seconds from start to finish!
second that. not only do they blame you for everything, they'll treat you as a repairman, calling you up anytime they have a "problem" and expecting you to give them the same service as a paid technician. its nice when people appreciate my efforts, but for the most part its quite pointless. i now restrict my services to close friends only who have manners and don't behave like i owe it to them.
I've set a few people up with old PII/350's, just to get them a computer in the first place..
I get similar requests about "what computer should I buy" at work, and usually a 350 is about all they need. But I still get "Is this the fastest you can get? Because I don't want to upgrade in 2 years". Well they'll probably upgrade in 2 years anyway or they wont reguardless of speed. So I just recommend they get some computer with an Athlon (not Duron) and that they don't spend more than $650 on it. Most other questions about RAM and disk space are moot because they're enough for most users now days even at the low end, and I don't want to get into explanations they probably won't understand.
If people want really advanced advice I usually only explain that they want a really good power supply, and a good main board (MSI makes pretty decent ones in my experience). Two critical components that no one ever looks at because they're focused on the processor.
"To confine our attention to terrestrial matters would be to limit the human spirit." -Stephen Hawking
Fatal error: Call to undefined function: message_die() in db/db.php on line 88
Yup, my hard drive did that a few weeks ago...
Chuck Norris: Socialism == a thousand years of darkness.
You probably mean you used one of those compression programs like Stacker or Double/DriveSpace.
The problem is that they don't know how much disk space you have, since it depends on the compressability of the data. Sometimes you would need to write something large to the drive, and the installer would tell you that there's not enough space, although it would have fit. That happens because some data compresses really well. A MP3 won't compress at all, but something like a 16 color image might compress really well.
So, for these cases you can adjust the estimated compression ratio. You tell the program you expect files will compress to 1/8 of their size, and it adjusts the free space estimation. That's all. Data won't compress any better because of it. I saw lots of people setting a huge compression ratio thinking that seeing 10 times more "free space" would somehow let them put 10 times more stuff on it.
For a demonstration, I made a "32 MB" 1.44MB floppy, and showed how it got full with 2 MB of files.
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Magnetic disk drives have been at the heart of computer systems since the early 1960s. They brought not only a significant advantage in processing performance, but also a new level of complexity for programmers. The three-dimensional geometry of a disk drive replaced the simple, linear, address spacetape-based programming model.
Whatever happened to cylinders and tracks?
Traditionally, the programmer's working model of disk storage has consisted of a set of uniform cylinders, each with a set of uniform tracks, which in turn hold a fixed number of 512-byte sectors, each with a unique address. The cylinder is made up of concentric circles (or tracks) on each disk platter in a multiplatter drive. Each track is divided up like pie slices into sectors. Because any location in this three-dimensional storage space could be uniquely identified by the cylinder number, head (surface) number, and sector number, this formed the basis for the original programming model for disk drives: cylinder-head-sector access.
This raises the question: If that is how data is stored on a drive, why don't we still use that as the programming model? The answer is not an easy one but has its roots in the fact that this geometric model endured until the advent of the intelligent inter-faces, SCSI and ATA. [The IBM mainframe world used a slightly different model, allowing tracks to be written with records (blocks) of user-defined length. An individual track could have sectors of different sizes. As one who programmed count key data (CKD) storage, I can attest that it offers the application wonderful flexibility, but the drive design challenges have relegated it to history. Also, a purist might point out that standards etiquette calls for SCSI to use blocks and ATA to use sectors, but I will use these terms interchangeably.]
Disk-interface protocols implement the programming model for disk drives. The earlier drive interfaces did little more than expose signals to let the host directly manipulate the drive mechanism and initiate a transfer of data at a target location. This put the task of dealing with all the low-level idiosyncrasies peculiar to drives on the programmer charged with developing the firmware or software support.
The introduction of ATA and SCSI fundamentally changed this. Table 1 describes the migration of intelligence from host to drive in the evolution of the more important interfaces. With these intelligent interface protocols, the task of programming the use of disk drives became much easier. Disk-drive designers also gained a freedom of action needed to design higher-capacity and higher-performance drives. I will look at just how drive designers used this freedom of action in their designs, but it is important first to understand the fundamental goal behind drive design: increasing areal density.
DAVE ANDERSON, director of strategic planning for Seagate Technology, has more than 20 years of experience in the computer field. His responsibilities include overall strategy for all disk interfaces. He has been involved in the architecture and planning of Fibre Channel since it was first proposed as a disk interface. He was also one of the principal architects of the disk XOR commands that are now a part of the standard