 Rereen normally required if errors are encountered.
 Data is not current.
 Error correction is more difficult.
Question 2. Online Processing System?
- Def: Inputs data enters the computer directly as soon as it is being
transacted. There information will be processed immediately and updated
into the master file.
- Ads:
 Enter availability of information for decision making.
 More accurate data capture.
 Schedules suits user.
- Dis:
 CPU time is used less efficiently.
 Random arrival of transactions, terminal operator process
each transaction separately.
 More expensive than batch processing.
Question 3. Real Time Processing System?
- Def: One which controls the environment by receiving data processing
them and returning results sufficiently quickly to affect the functioning of
the environment at that time.
- Ads:
 Response time is very critical and sufficient quick.
- Dis:
 Expensive hardware & software.
 Very complex in terms of hardware & software.
Chapter 4: PRINTERS AND TERMINALS.
Question 1. Classification of printers?
1. Classifying printers according to speed.
a. Serial printers
Slow printers that print one character at a time.
Eg: Dot matrix printers

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Kinds of quality printers
Draft quality
Near letter quality(NLQ)
Letter quality
Graphic quality
Question 2. Describe some types of printer?
1. According to speed:
a. Dot matrix printer
- Serial impact printers that can print draft, near letter quality and a limited
amount of graphics.
- The print resolution is generally lower than lazer printers.
b. Daisywheel printers
- Are serial impact printers, the speed of a daisywheel printer is slow(20-55
characters per second), noisy in operation.
- The print head has the letters arranged at the end of spokes round a central
hub.
c. Chain printers
- The chains printers has its characters set rapidly rotating on a print chain.
d. Band printers
- The band printer has rotating scalloped steel band.
e. Drum printers
- Are line printers, the print character are raised in bands around a heavy
metal drum which rotates at very high speed.
- The print hammers strike the paper and a print ribbon against an apropriate
character on the line. An entire line of the same character is printed on one
rotation of the drum.
f. Thermal printers
- Uses special heat sensitive paper and a matrix of print wires that become
hot when exposed to an electric current. The heated wires come into close


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- The required characters are formed as an electric charge image on the
cylinders surface.
- Toner is the applied to the charged image and transferred to the paper on
which it is transfixed by pressure(cold fusion).
j. Electrostatic printers
- Letterheads and logos are created electrostatically from a changeable
metal cylinder.
k. Magnetic printers
- A drum in the printer has a surface that can be coated with sows of tiny
spots of magnetion by means of thousands of minute recording heads.
- As the drum rotates it becomes covered with these magnetic spots so as to
from a latent image of the page to be printed.
- Dry ink particles are brought into contact with the drum’s surface and
these adthere to the magnetised spots. The ink was then pressunal on to the
surface and subsequently transferred onto the paper.
Question 3. Characteristics of a page printers?
- Speed
- Characters sets
- Copies
- Intelligence
- Output
Chapter 5: DATA STORAGE MEDIA.
Question 1. Data storage Requirements Characteristics?
- Low access time: fast speed
- Storage capacity: much enough
- Interchangeability: can be change easily
- Security: safe enough
- Transfer rate: fast enough

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
 Certain models of disk units also have a number of fixed
read/write heads in addition to the movable heads.
 The fixed head are positioned permanently over certain of
the outer tracks, there being one head per track, so
climimating the need for head movement.
- The heads are very close disk surface.
- Curshion of air carried by the rotating disk.
Question 3. Winchester disks( hard disks )?
- Comprises a number of platters(disks) permanently into an airtight
enclosure.
- All dust is excluded thus perimiting the read/write heads to be positioned
even closer to the surfaces and so enabling greater recording densities to
be employed.
- The disks have greater storage capacity and a higher rate of data transger.
- It has the lubricated surfaces allowing the heads “land” when the platters
cease to rotate, so eliminating head crashes.
- Winchester platters are either 14 in, 8 in, 5¼ in or 3½ in diameter.
Question 4. Floppy disks?
- Diskettes, generally called floppy disks, are single disks made of flexible
plastic and permanently housed is an envelope.
- The data on floppy disks is in concentric tracks on the outer part of the
surfaces and access to it is via slot in the envelope.
- The most common size are 3½ in, 5¼in, and 8 in diameter disks, the 3½ in
disks have the advantages of a shutter.
- Floppy disks may be either single or double sided and of course the drive
needs to be correspondingly equipped.


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- Optical disks rotate mostly at 1500 r.p.m which, allowing for the
movement of the laser unti, given access time of between 16 & 500 ms and
data transfer rates of 0.6 to 3 MVs per second.
- The draw back of optical disks is that the data cannot be erased so making
them non-rewriteable.
Question 6. Mass storage media?
- Mass storage media is a high capacity disk system as when necessary by
transferring data from a number of “data cartridges” house in cells.
- Each cartridge consists of a 3 in wide magnetic modium inside a protective
cover
- In order to load the disk system, the data cartridges are moved
automatically from the cells.
- A typical system consists of 9440 cartridges giving a storage capacity of
472000 million bytes.
Question 7. Magnetic drums?
- A magnetic drum consists of a cylinder upon the surface of which data is
stored in magnetic form in tracks running around its circumference, each
track has its own read/write head.
- A typical magnetic drum has 800 tracks each capable of holding 5000
bytes.
Question 8. Charge_coupled Device Memory (CCD)?
- CCD consists of thousands tiny metal squares each capable of holding an
electric charge, thus representing a bit.
- The squares are in the form of an array 64 x 64 holding 4096 bits.
- It is very impact.
- CCD is volate lity storage.
Question 9. Magnetic Bubble Memory?
- A thin wayer of magnetic garnet is capable of containing tiny domains or

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