Secondary Storage

HARVEY M. DEITEL , BARBARA DEITEL , in An Introduction to Information Processing, 1986

Floppy Disks

Floppy disks , sometimes called flexible disks or diskettes, can store between a few hundred thousand and several million characters of information (Figures 6-17 and 6-18). It takes only about a tenth of a second for a floppy disk drive to retrieve any piece of data directly. The disk's small size and low cost (only a few dollars each) helped spawn the personal computer revolution in the late 1970s.

Figure 6-17. Floppy disks are most commonly sold in the 5¼- and 8-inch sizes. Smaller floppies are also available.

Figure 6-18. Inserting an 8-inch floppy disk into a floppy disk drive.

The heart of a floppy disk, or floppy, is a circle of magnetic material (Figure 6-19). Information is recorded in circular tracks in turn divided into wedge-shaped sectors (Figure 6-20). The hardware is designed to access the disk by sector number. Disks may be hard-sectored or soft-sectored. On hard-sectored disks, sectors are physically marked by a series of holes near the center of the disk. On soft-sectored disks, sector locations are magnetically recorded on the disk. Recording this sector information is called formatting or initializing the disk.

Figure 6-19. Inside the protector of a floppy disk is the circular disk itself and a special fabric that cushions and cleans the disk.

Figure 6-20. Here the data is recorded in equal-sized blocks, called sectors.

Before the invention of floppy disks by Shugart Associates in 1972, personal computers used small cassette tapes (Figure 6-21), which have neither the speed nor reliability needed by computer systems. Floppies are so reliable that some manufacturers certify that their disks are error-free at time of purchase and will remain error-free for 10 million passes under a read/write head (See also Figures 6-22 and 6-23).

Figure 6-21. Tape cassettes and cartridges.

Figure 6-22. Floppy disk drives are reliable and require little maintenance. Here the operator is inserting a special cleaning diskette into the drive. The whole process requires only a few minutes about once a month.

Figure 6-23. Many types of storage units are available for filing floppy disks.

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File Management

William J. Buchanan BSc, CEng, PhD , in Software Development for Engineers, 1997

32.2.3 Formatting a disk

A floppy disk must be formatted before it can store files. Some disks are pre-formatted when they are purchased, but others required to be formatted before they are used. Care must be taken when formatting a disk as the current contents of the disk will be erased.

To format a disk first insert it into the floppy disk drive. Next select Disk→Format disk … from the menu, as shown in Figure 32.5. When this is selected Windows will prompt the user for the drive which the disk has been entered and the capacity of the disk. By default this is likely to be set to A: and 1.44 MB (for a 3.5 inch floppy disk drive on the A: drive), respectively. If the drive differs from the default or its format differs then change the options by pulling down the Disk In or the Capacity options.

Figure 32.6 shows the main steps that are taken to format the disk. First the disk capacity and drive name are prompted for. When these are correct the OK button is selected. Next a Format Disk window is displayed. Within this window the current status of the disk formatting operation is displayed (from 0 to 100% complete). When complete, a window with a message Creating root directory will be displayed. After this the formatted disks' capacity is displayed and the user is prompted as to whether another disk is to be formatted. If no more disks are to be formatted then the No option is selected else Yes is selected. Note that the Cancel option on any of the format status windows can be selected to cancel the format process.

Figure 32.6. Formatting a floppy disk

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Computers and their application

Ian Robertson , in Mechanical Engineer's Reference Book (Twelfth Edition), 1994

4.12.6 Floppy disk

The floppy disk, while having the four elements described above, was conceived as a simple, low-cost device providing a moderate amount of random access back-up storage to microcomputers, word processors and small business and technical minicomputers. As the name implies, the magnetic medium used is a flexible, magnetic oxide-coated diskette, which is contained in a square envelope with apertures for the drive spindle to engage a hole in the centre of the disk and for the read/write head to make contact with the disk. Diskettes are of three standard diameters, approximately 203 mm (8-inch), 133 mm (5 1/2-inch) and 89 mm (3 1/2-inch). The compactness and flexibility of the disk makes it very simple to handle and store, and possible for it to be sent by post.

One major simplification in the design of the floppy disk system is the arrangement of the read/write head. This runs in contact with the disk surface during read/write operations and is retracted otherwise. This feature and the choice of disk coating and the pressure loading of the head are such that, at the rotational speed of 360 rev/min, the wear on the recording surface is minimal. Eventually, however, wear and therefore error rate are such that the diskette may have to be replaced, copying the information onto a new diskette.

Capacities vary from the 256 kilobytes of the earliest drives, which record on one surface of the diskette only, to a figure of over 2 megabytes on more recent units, most of which use both surfaces of the diskette. Access times, imposed by the rather slow head-positioning mechanism using a stepping motor, are in the range of 100-500 ms. Transfer rates are below 300 kilobytes per second.

Another simplification is in the area of operator controls. There are generally no switches or status indicators, the simple action of moving a flap on the front of the drive to load or removing the diskette being the only operator action. The disk motor spins all the time that a disk is present.

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Optical Information Processing

Mir Mojtaba Mirsalehi , in Encyclopedia of Physical Science and Technology (Third Edition), 2003

VI.C.3.a Optical disks

Today, magnetic hard disks and floppy disks are widely used in electronic computers. A relatively new medium for data storage is optical disks, where the information is recorded and read by a laser beam. The main advantage of optical disks is their high storage capacity. A small 3.5- or 5.5-in. Optical disk is capable of storing 30 to 200  Mbytes of information.

Optical disks are of two types: read-only disks and read–write (erasable) disks. The first type is useful for archival storage and storing data or instructions that do not need to be changed. In the second type, the recorded data can be erased or changed. This type of memory is needed for temporary data storage, such as in digital computing. Some of the materials used for nonerasable disks are tellurium, silver halide, photoresists, and photopolymers. Among the candidate materials for erasable disks, three groups are more promising. These are magneto-optic materials, phase-change materials, and thermoplastic materials.

Optical disks are now used in some models of personal computers, and they are expected to become more common. Also, optical disks have been used for archival storage. Two such systems have been developed and installed by RCA for NASA and Rome Air Development Center in 1985. These are optical disk "jukebox" mass storage systems that provide direct access to any part of a stored data of 1013 bits within 6   sec. These systems have a cartridge storage module that contains 125 optical disks, each of 7.8   ×   1010 bits storage capacity. This storage size is beyond the capacities that are currently available with other technologies.

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THERMAL PERFORMANCE ANALYSIS FOR ELEVEN CALIFORNIA PASSIVE SOLAR AND ENERGY CONSERVING HOUSES BASED ON ONE YEAR OF MONITORED DATA

Sukhbir Mahajan , ... Patrick Morandi , in Passive and Low Energy Architecture, 1983

QUALITATIVE ANALYSIS OF INSTRUMENTED DATA

The hourly data on cassette tapes was transferred to floppy discs and nine track tape for processing and plotting using other computer medium. One of the first steps in processing the data was to plot the output of various sensors for three to five day periods during winter and summer months. These plots provide qualitative information on the performance of the houses. As an example shown in Fig. 3 are plots of four sensors from the Santa Barbara house for two clear days followed by a cloudy day in January. This plot shows how the Trombe wall passive solar system response to solar inputs, the charging and discharging of the thermal mass, and occupant activities. The double peaks on the inside temperature plot are first, due to solar gain and the second, due to occupant activities such as cooking and use of appliances and the delayed heat pulse from the Trombe wall. As expected the heat pulse through the Trombe wall arrives about 8 hours after the peak solar gain. The transition from the two sunny days to the cloudy day is quite good and due mainly to the exponential decay of the Trombe wall thermal mass temperature. Other qualitative plots which are used in this way are the daily max-min temperature plots and the interior "binned" temperature bar graphs. With this level of information a good picture of how the house was operated and a qualitative understanding of the performance is possible.

Fig. 3. Hour-by-hour plot of four sensors in the Santa Barbara Trombe Wall house.

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Motherboard Design

William Buchanan BSc (Hons), CEng, PhD , in Computer Busses, 2000

5.1.4 82091AA (AIP)

The AIP device integrates the serial ports, parallel ports and floppy disk interfaces. Figure 5.3 shows its connections and Figure 5.4 shows the interconnection between the AIP and the PIIX3 device. The OSC frequency is set to 14.218 18   MHz. It can be seen that the range of interrupts for the serial, parallel and floppy disk drive is IRQ3, IRQ4, IRQ5, IRQ6 and IRQ7. Normally the settings are:

Figure 5.3. API IC

Figure 5.4. Connections between TXC, PIIX3 and AIP
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IRQ3 – secondary serial port (COM2/COM4).

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IRQ4 – primary serial port (COM1/COM3).

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RQ6 – floppy disk controller.

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IRQ7 – parallel port (LPT 1).

Figure 5.4 shows the main connections between the TXC, PIIX3 and the AIP. It can be seen that the AIP uses many of the ISA connections (such as 0WS#, IOCHRDY, and so on). The interface between the TCX and the PIIX3 defines the PCI bus and the interface between the PIIX3 and AIP defines some of the ISA signals.

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Computers

Owen Bishop , in Understand Electronics (Second Edition), 2001

Disk drives

Most computers have three kinds of disk drive. The floppy disk drive stores data on a thin flexible plastic disk coated on one or both sides with a magnetic film. Although the disk itself is floppy, and early ones were enclosed in flimsy cardboard covers, most disks are nowadays enclosed in a stiff plastic cover. The cover has a metal shutter which slides back automatically when the disk is inserted in the drive to expose part of the disk surface to the magnetic head.

The principle is the same as that used when recording music on digital audio tape. The main difference is that the data is recorded on 40 concentric tracks and the magnetic head moves radially to read or write each track. Each track is divided into sectors, each one being allocated to one particular program or set of data. Longer programs or data tables may require more than one sector. There is a directory track on the disk telling the computer in which track and sector to look for each block of stored data and the magnetic head can skip from track to track and sector to sector, finding the information that is required. A typical floppy disk can store up to 1.4 megabytes of data.

Data can be read at rates of several hundred bits per second, but first the disk must be accelerated up to full speed (360 r.p.m.), and the magnetic head moved to the correct track and sector. A typical access time is 200 milliseconds, which is much slower than the 25 to 150 nanosecond access time of RAM or ROM.

A hard disk drive has one or more disks attached to the same spindle. The disks are made of non-magnetic metal and coated on both sides with a magnetic film. The principle of storage is the same but the magnetic heads are much closer to the film. This is because the disks rotate at very high speeds (about 3600 revolutions per minute). This gives rise to a thin layer of moving air close to the disk surface in which the magnetic head 'floats' without actually coming into contact with the disk. Since the head is closer to the disk, it is possible to record data more densely: the tracks are closer together and the recorded bits closer together than on a floppy disk. Consequently, a typical hard disk drive stores several gigabytes (thousand million bytes). Another advantage of the hard disk is that the high rate of spin reduces access time to about 20 milliseconds. As the head is very close to the surface of the disk it is essential to exclude particles of dust or smoke. Hard drives are sealed during manufacture and can not normally be opened by the user.

Compact disc drives are very similar to CD players and work on the same principles. In fact, they are able to play ordinary music CDs through the sound card of the computer. The information stored on a CD is simply a series of 0   s and 1   s. It may represent musical sounds but it could equally well be used for storing information of other kinds. In computing terms, a CD stores about 600 megabytes of data. CDs have largely replaced floppy disks as a medium for distributing software. Most programs nowadays are too long to fit on a floppy disk and there are other advantages too. A CD is unaffected by stray magnetic that can so easily wipe the data from a floppy disk. Also, CDs cost much less to produce in quantity than floppy disks, so are ideal for large-scale distribution, on the covers of computer and other magazines, for example.

Like hard disk drives, CD drives are fast enough to be used as memory storage devices for computers, the data being accessed straight off the CD. The main difference is that CDs are read-only memory (CD-ROM). However, CD- recordable drives may be used with special CD-R discs to write (but not re-write) data and play it back as many times as required. CDs are widely used in multimedia technology. A disc can store text, computer programs, photographs and diagrams, motion pictures and sound. These can be accessed and loaded into the computer almost instantly. Very elaborate games with startling graphics are now available on CD-ROM but more serious applications of the technology include educational and reference discs.

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Computer Architecture

Morris Chang , in The Electrical Engineering Handbook, 2005

Magnetic Disk Memory

Magnetic disk memory is used to implement hard disks, standard floppy disks, and high-density floppy disks (e.g., Zip drive, Super drive). Hard disks are the most commonly used second memory devices because of their low cost, high speed, and high storage capacity. Hard disk drives are mass storage units that allow read to and write from magnetic media; they consist of one or many thin disks that have magnetic coating, allowing data to be recorded. The recording surface is divided into concentric tracks, and each track is divided into segments called sectors. The set of tracks at a given radial position is referred to as a cylinder. One disk or more are then mount on a spindle and rotate at a constant speed. To access the data, a two-step process is required. First, the read/write head moves across the rotating disk to the locating track. Then the head waits until the right sector is underneath it, and read/write is performed. The descriptions of magnetic disk memory devices are given as follows:

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The hard disk drive is the most commonly used mass storage device, as already stated. The size of today's hard drives can vary from 14 inches (used in older mainframe computers) to 1.8 in (used in laptop and portable computers). The most typical size used in a PC is 3.5 in, and the ones used in notebook computers are from 1.8 to 2.5 in. The rotating speed also varies depending on the interface used (discussed more in the bus interface section). For an integrated drive electronics (IDE) interface, the speed varies from 4500 rpm to 7200 rpm. For a small computer systems interface (SCSI), the speed can be as high as 10,800 rpm. The typical capacity varies from one gigabyte to tens of gigabytes (1 GB is 230 bytes).

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The floppy disk drive, also known as diskette, is a removable magnetic storage medium that allows recording of data. IBM first introduced it as a 8-in diskette in 1971. In the middle of 1970s, a 5.25 diskette was introduced. Today, the most commonly used floppy disks are 3.5 inches and have the capacity of 800 KB to 2.8 MB (with a standard of 1.44 MB).

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The high-density floppy disk drive was first introduced in 1995. High-density floppy disks, while sharing a 3.5-in size with the standard floppy disks, are much faster and have up to one hundred times more capacity than the standard floppy disks. One example is the Zip drive, produced by Iomega. Each Zip disk is capable of storing up to 100 MB of data. Similarly, Imation, a subsidiary of 3 M, also manufactures the Super disk (also known as the LS 120) that can store up to 120 MB of data.

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The removable hard disk has been at work in the mainframe computer industry since the 1950s. Back then, the drive mechanism was extremely expensive; therefore, different applications would use different removable disks, during program execution. In the 1980s, removable hard drive was used for backup purposes. The capacity then was 44 MB. Nowadays, removable disks come in various capacities from one gigabyte up to several gigabytes.

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The redundant array of inexpensive disks (RAID) was introduced by David Patterson and other researchers at the University of California, Berkeley, in the late 1980s. It is a method where two or more disks are used to store data. Data can be read simultaneously from more than one drive, which improves the performance. Data can also be split among all drives in bits, bytes, or blocks. Typically two or more disks are connected together. A single controller can be used to connect the drives so that they function together as one drive. For extra safety, a second interface controller can be installed to duplex the drives and increase read performance. The major advantages of RAID are improvement in reliability and protection for data in mass storage systems.

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The hardware/software integration phase

Arnold S. Berger PhD , in Debugging Embedded and Real-Time Systems, 2020

The case of the nonstandard hard disk drive interface

Hewlett-Packard introduced its Vectra Portable CS computer in 1987, and it contained a floppy disk drive and a 20  MB, 3.5″ hard drive. The company had high hopes for the portable, but it failed in the market. Here's the description from the HP Computer Museum [2]:

The Vectra Portable CS was the portable version of the Vectra CS. The Portable CS had a large LCD screen as well as CGA adaptor for use with an external monitor. The Portable was offered in two mass storage configurations: dual 3.5 inch (1.44 MB) floppy disc drives - P/N D1001A, or a floppy disc drive and a 20 MB hard disc drive - P/N D1009A. The Portable CS did not succeed due to its large size (much larger than the Portable Plus), relatively high price and non-standard media (3.5 inch discs).

The Portable Vectra CS was introduced on September 1, 1987. It was discontinued on May 1, 1989.

The company had high hopes of selling the hard drive as an OEM product to other computer manufacturers because it was one of the first hard drives out in the 3.5″ form factor. Rather than adopt the industry standard integrated drive electronics (IDE) interface, developed by Compaq and Western Digital in 1986, they designed an interface that used a 40-pin connector, but otherwise, was entirely different. As a result, the drive was never adopted by other manufacturers and HP discontinued manufacturing soon after. The lesson? Standards matter.

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Assembly Costing

K.G. Swift , J.D. Booker , in Manufacturing Process Selection Handbook, 2013

13.4.2 Floppy Disk

This second case study is concerned with the assembly time and cost of a 1.44 Mb floppy disk for use with a personal computer. Although this product is almost outmoded in this digital age, it is a useful product line to further demonstrate the methodology for costing assemblies. Figure 13.8 shows the component parts.

Figure 13.8. Floppy Disk Component Parts.

The results are shown together with the assembly structure diagram in Figure 13.9 and a full assembly costing analysis is provided in Figure 13.10. The total assembly cost of the floppy disk per unit is found to be approximately ≤0.24 ($0.39) and the calculated assembly time is approximately 52 seconds. Note that a relaxation is not taken into account and the fact that the operator would be working in a clean environment room wearing protective clothing to stop contamination.

Figure 13.9. Assembly Structure Diagram for a Floppy Disk.

Figure 13.10. Floppy Disk Assembly Costing Analysis.

The time contribution of each assembly operation compared to the overall assembly time is shown as a percentage in Figure 13.11. A Pareto chart format is used with the greatest contribution to the total assembly time to the left. As highlighted, locating the front case sub-assembly on to the back case sub-assembly whilst the spring is in position is a difficult and time-consuming assembly task. Screen placement and spring fitting are two other operations of a time-consuming nature. In order to improve the ease of assembly of a particular concept design and reduce assembly costs, the use of the metrics in this manner can help identify potentially problematic areas and give guidance on redesign through reference to the charts provided.

Figure 13.11. Pareto Chart of the Assembly Operation Times for the Floppy Disk.

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