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- Generalities


- The disk drive

- Hard disks

- Removable devices
  - up to 250 MB
  - up to 2 GB
  - of more than 2 GB

- Safety copies (backups)

Updated page
11/22/2000


Author:
Juan Herrerías Rey
 

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Storage


 

Diskette units

For bad and antiquated that is a computer, always has at least one of these devices. His capacity is completely insufficient for the current needs, but they are provided with the advantage that they give them many years that go like absolute standard for portable storage.

5,25 inches diskette

Standard? Well, perhaps not so much. From that one distant 1.981, the world of the PC has known almost ten types different from diskettes and from readership for the same ones. Originally the diskettes were flexible and quite big, approximately 5,25 inches wide. The first capacity of 160 Kb was revealed at once how insufficiently, for what began growing and did not stop up to 1,44 MB, already with the current, smaller diskettes (3,5 "), more rigid and protected for a metallic eyelash.

There even exists a 2,88 MB model and 3,5 " that were incorporating some computers IBM, but it did not go so far as to come off because the discs were turning out to be slightly expensive and kept on being too scarce for somewhat serious applications; many people think that up to 100 MB of a Zip they are insufficient. Any way the most common types of diskettes appear in the following table:

Size

Type of disc

Capacity

Explanation

5,25"

SS/DD

180 Kb

An expensive, double thickness. Desfasado

5,25"

DS/DD

360 Kb

Two faces, double thickness. Desfasado

5,25"

DS/HD

1,2 MB

Two faces, high thickness. Desfasado but useful

3,5"

DS/DD

720 Kb

Two faces, double thickness. Desfasado but very common

3,5"

DS/HD

1,44 MB

Two faces, high thickness. The current standard

The disk drives are compatible "backwards"; that is to say, that in a disk drive of 3,5 " high thickness (of 1,44 MB) we can use discs of 720 Kb or of 1,44 MB, but in one of double thickness, more ancient, we can only use them of 720 Kb.

Diskette 3,5 inches high thickness

Certainly, to distinguish at first sight a disc of 3,5 " high thickness of other of double, it is enough to observe the number of holes that it presents in his low part. If it has the only one placed in the left side of the image and generally provided with a mobile eyelash, it is a question of a disc of double thickness; if it has two holes, there is no doubt that it is a question of a disc of high thickness. If the first one of the holes is to the overdraft the disc will be protected against writing; the second one only serves to differentiate both types of diskettes.

Any way the diskette will have to be formatted to the correct capacity, for which we can use the order FORMAT of TWO or the menus of Windows (personally, I prefer the order of TWO). It must be born in mind that if we do not specify anything, the disc will try to be formatted to the nominal capacity of the disk drive, what with a disc of low capacity can be a disastrous error. For example, next some common formatting orders appear:

Formatting order

Explanation

FORMAT A:

It gives format to the disc of the unit "A" to the nominal capacity of the disk drive

FORMAT B: /F:720

It gives format to the disc of the unit "B" to 720 capacity Kb

FORMAT A: /S

It gives format to the disc of the unit "A" to the nominal capacity of the disk drive and copies the system files (that is to say, it creates a basic starter disc)

The normal computers have a port for two disk drives, which will be connected to the only information cable. The one that is connected in the end of the same one will be the first one (her "To" in TWO) and the one that is in the second connector, between the computer and the previous disk drive, will be the second one (the "B").

It turns out to be common to have a computer that turns out to be sufficient for the tasks for that we ask him, but that has a disk drive of an antiquated model, well of 5,25 " or of 3,5 " of double thickness, for which even it can be difficult to find appropriate discs (especially in case of those of 5,25 "). In such a case, he is worth installing a modern disk drive of 3,5 " and 1,44 MB, since they cost less than 5.000 pts and it is one of the tasks simplest of doing, as he explains himself in this hypertie.

The diskettes have reputation of being a few very little trustworthy devices as for the long-term storage of the information; and in effect, they it are. Everything imaginable affects them: magnetic fields, heat, cold, moisture, blows, dust... It does a time I verified approximately 25 diskettes of different marks of an ancient one 286, which were kept in a plastic box for diskettes, and almost the half was not working, what I did not surprise by no means.

If you have programs on diskette, do copies immediately and keep the originals in sure place. If you have important information stored on diskette, do new copies and think about another better storage method. And first of all, always buy mark diskettes. They will not save him from the future mistakes, but at least they will be more or less well of origin; the economies in these topics are bad partners, flee of the diskettes got into white boxes without logotypes as of the pest or it will weigh him...

 

Hard disks

Hard disk without the casing

There are other of the habitual elements in the computers, at least from the times of 286. A hard disk is composed of numerous discs of material sensitive to the magnetic, piled up fields some on others; in fact it looks alike very much to a diskettes battery without his cases and with the mechanism of draft and the reading arm included in the casing.

The hard disks have evolved very much from the primitive models of 10 ó 20 MB. At present the sizes perform the order of several gigabytes, the average access time is very low (less than 20 ms) and his transference speed is so high that they must turn to more than 5.000 rpm (revolutionize per minute), what unfortunately does that they warm up like demons, therefore it is not any foolery to install a fan to them for his refrigeration.

A fundamental difference between a few and other hard disks is his connection interface. Formerly diverse types were used, like MFM, RLL or ESDI, although at present only two are used: IDE and SCSI.

 

Hard disks IDE

The interface IDE (more correctly so called IT TIES, the standard of norms on which it is based) is most used in normal PCs, because it has a balance adapted enough between price and services. The hard disks IDE are distributed in channels in which there can be a maximum of 2 devices for channel; in the standard initial IDE only he was getting ready of a channel, therefore the maximum number of devices IDE was 2.

The standard IDE was extended by the norm ATA-2 in what it has happened in naming EIDE (Enhanced IDE or improved IDE). The systems EIDE have 2 channels IDE, primary and secondary, with what they can accept up to 4 devices, that they do not have porqué to be hard disks while they fulfill the norms of connectors ATAPI; for example, the CDs-ROMs and some units SuperDisk appear with this type of connector.

In each of the channels IDE there must be a Main device (master's degree) and another Slave (slave). The teacher is the first one of the two and it usually place at the end of the cable, the letter being assigned generally "C" in TWO. The slave is the second one normally connected in the center of the cable between the teacher and the checker, who often is integrated to the proper motherboard; the letter would be assigned to him "D".

The devices IDE or EIDE like hard disks or CD-ROMs have a few microswitches (jumpers), placed generally in the later or low part of the same ones, which allow to select his teacher character, slave or even other possibilities like "teacher without slave". The positions of the jumpers are indicated in a sticker in the surface of the disc, or in the manual or serigrafiadas in the badge of circuit of the hard disk, with the letters M to designate "teacher" and S for "slave".

Other advances in speed come from the access ways:

Access way

Theoretical maximum transference

Comment

PIO-0

3,3 MB/s

On very ancient discs, of 100 MB or less

PIO-1

5,2 MB/s

On ancient discs, of minor capacity of approximately 400 MB

PIO-2

8,3 MB/s

PIO-3

11,1 MB/s

Typical on capacity discs between approximately 400 MB and 2 GB

PIO-4

16,6 MB/s

DMA-1 multiword

13,3 MB/s

Ways of doubtful utility, since his speed is not major than in the way PIO-4

DMA-2 multiword or DMA/16

16,6 MB/s

UltraDMA (DMA33 or UltraDMA way 2)

33,3 MB/s

The standard even does very little

UltraDMA66 (ATA66 or UltraDMA way 4)

66,6 MB/s

The current standard; it uses a cable of 40 pines and 80 drivers

Although in this area the theoretical numbers of maximum transference fight between the hard disk and the PC, which physically the disc can reach internally; 66,6 MB/s is absolutely unattainable for any current hard disk. In fact, to come to 25 MB/s with a hard disk UltraDMA is slightly quite difficult to manage, at present the habitual numbers are rather for approximately 10 to 20 Mb / century

The ways IT CHIRPED they are enabled generally by means of the BIOS and give few problems, although on not current hard disks sometimes the autodetection of a PIOUS way gives a way a grade superior to the one that really he can support with reliability, it happens very much for example with discs that are identified like PIO-4 but that are not trustworthy any more than to PIO-3.

The ways DMA have the advantage of which they liberate to the microprocessor of big part of the work of the transference of information, taking charge it to the chipset of the badge (if it is that this one has this capacity, as it happens from the times of Intel Tritón), something similar to what does the technology SCSI. Nevertheless, the activation of this characteristic (known like bus mastering) needs to use the suitable drivers and can give problems with the CD - ROM, therefore in fact the only useful way is the UltraDMA (and I have not even commented much desfasados on ways DMA singleword).

It is necessary to bear in mind that the activation or not of these characteristics it is optional and the compatibility backwards is guaranteed; we can buy a hard disk UltraDMA and use it in way PIO-0 without problems, we will only be throwing the money. So if he wants a disc for 486 that does not support bus mastering, he does not worry: buy a disc UltraDMA and select the way PIO-4, scarcely it will appreciate the yield difference and the installation will be even simpler.

For more information about hard disks IDE like the handling of the BIOS, the way LBA for discs of more than 528 MB, configurations of jumpers and the others, I recommend to consult my page on Installing a hard disk.

 

Hard disks SCSI

On this interface we have already spoken earlier in the generalities paragraph; only to stress that the advantage of these discs is not in his mechanics, that it can be identical to that of one IDE (the same rotation speed, the same average access time...) but in that the information transference is more constant and almost independent from the load of work of the microprocessor.

This does that the advantage of the hard disks SCSI is valuable in computers loaded with work, like servants, computers for CAD or video, or when multitask of intensive form is realized, while if the only thing that we want is to load Word and to do a letter the yield difference with a disc UltraDMA will be invaluable.

On the discs SCSI it turns out to be rare to come to 20 MB/s of theoretical transference of the way Ultra SCSI, and not of background to 80 MB/s of the way Ultra-2 Wide SCSI, but yes to numbers perhaps attainable but never surmountable for a disc IDE. Of what there is no doubt the fact is that the discs SCSI are a professional option, of price and high services, therefore the manufacturers always choose this type of interface for his discs of major capacity and speed. It turns out to be frankly difficult to find a hard disk SCSI of bad quality, but due to his high price it is convenient to protect our investment looking for one with a guarantee of several years, 3 ó more therefore it could happen... although it is improbable.

 


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