Computer system
Computer System
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Book I: computer system fundamentals.
Chapter 1: INTRODUCTION TO COMPUTER.
Question 1. What is a computer?
A computer may be defined as a machine which accepts data from an input device, processes it
by performing arithmetical and logic operations in accordance with a program of instructions and
returns the results through an output unit.
A computer is basically an electronic machine operating on current.
Question 2. Components of a Computer system?
A computer system comprises of the following components:
1. Central Processing Unit (CPU).
- CPU is the heart of the whole sys
- CPU consists of the :
• control unit (CU)
• arithmetic logic unit (ALU)
• accumulator (ACC)
• program counter (PC)
• instruction register (IR)
• memory address register (MAR)
• memory data register (MDR)
• status register (SR)
• general purpose register
- The function of each components of CPU:
• Control unit:
 control and co_ordinate all hardware functions of the CS.
 examine and decode all program instructions to the computer and
initiate their execution by sending the appropriate signals.
• ALU:
 performs all arithmetic <addition, subtraction, multiplication,

Control unit
Arithmetic Logic Unit
Accumulator
Program Couter to main
Instruction Register memory
Memory Address Register
Memory Data Register
Status Register
General Purpose Register
Basic components of a CPU. Control Unit
Input Unit ALU Output Unit

Main Memory
Backing Storage
Control signals
Data flow
Components of a CS.
2. Input units
- Used to enter data( raw unprocessed facts) and instructions to the computer.
3. Output units
- Used for delevering the processed result from the computer in useful form.
4. Backing storage units
- Backing storage units need for high capacity data storage devices that can store
data in a more permanent form for later retrieral, updating and referencing.
- Backing storage is also called secondary storage external storage and auxiliary
storage.
Chapter 2: MICOPROCESSOR.

 Response time is not critical.
 Need to process large volumn of data.
 Computer efficiency is more important than response time.
- Dis:
 Time between recording and processing of source document is long
 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.
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A3
A1
A2
A2
A3
A1
- 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

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.
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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 contact with the
paper, burning the image of the character onto it.
- The more advanced thermal printers are using thermal transfer printing.
- They have a special heat sensitive ribbon and a print head with wires that become

Question 3. Characteristics of a page printers?
- Speed
- Characters sets
- Copies
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- 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
- Cost: economic
Question 2. Magnetic disks?
- This comprises a drive unit onto which one or perhaps two magnetic disk
cartridges are loaded.
- The drive consists of a control unit and a spindle housing that rotates continuously
when switch on.
- The cartridge are loaded by the operator so as to provide the data currently needed
for the job in hand.
- Bach tracks is devided up into sectors(often 4 or 8), sectors are read or written or
more at a time as blocks by means of a read.
- There are usually one head for each surface, all the heads are moved.
- Sunchronously across the tracks.
- Once in position all the data on the equiradial tracks can be read or written
without further movement of the heads.
- Cylinder is a set of equiradial tracks.
- A cartridge comprises several flat disks mounted on a central sprindle. When

that they have come into extensive used by small business and home computer
buffs.
- The range of capacities is from 1/4 to 2 megabytes and transfer rates around 125
to 250 kilobytes per seconds.
Question 5. Optical disks?
- Optical disk are comparatively new development for data storage.
- Optical disks consist of a single removable glass, plastic or metal disk coated on
one side with tellurium and protected by a 1 mm layer or transpacent plastic.
- The disk diameters are mostly between 8 in and 14 in they rotate on a spindle in a
similar fashion to magnetic disks.
- The data is recorded in the form of minute pits burned into the telliurium coating
by a finely-focused lazer beam.
- Optical disks hold between 0.7 and GBs, this is about 20 times greater than
magnetic dis cartridges.
- The data is read by a low power laser beam which moved across the surface and is
reflected into a photo cell.
- 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?

Question 1. File Processes?
1. Sorting
a. The records in logical file are brought into some sequence as determined by key in
the records.
b. A computer is capable of sorting record into a “nested” sequence.
c. Sorting is done by a “sorting generator”. This is part of the computer’s software
and comprises several sophisticated sorting techniques that are called into use
according to the file and the sort requirements.
d. The need of sorting has dimished in line with the demise of magnetic tape as
backing storage.
2. Merging
- Merging implies that two or more files in the same sequence are combined into
one file.
a. File merging
 Two or more separate files of similar seconds and in the
same sequence are marged together so as to form one file.
b. Record merging
 The records from two or more “input” files, usually in the
same sequence, are combined one record in the output file.
3. Matching
a. Two or more input files (generally in the same sequence) are compared records
against record in order to ensure that there is a complete set of records for each
key.
b. Masmatched records are highlighted for subsequent action
4. Summanizing
a. Records with the same key in one file are accumulated together to form one
record in the output file.
b. Summanizing usually applies to a file presorted into a certain sequence and the
resultant file is in the same sequence.
c. Records to be summarized are generally of a similar type.

- Groups of unrequired records are skipped past.
- Indexed sequential files may also be accessed haphazandly.
4. Random modes:
- Each record is stored in a location determind from the second’s key by means of
an add generation algorithm.
- The only erricient way to find a record is to use the algorithm
- Random mode is applicable to master files
• Ads of random modes
 No index is required thus saving storage space
 It is a fast access method because little or no searching is involved
 Transaction do not need storing, thus saving time
 New records are easily insertly into the random file provided they
are not excessive in number
• Dis
 The main problem with the random mode is in achieving a uniform
spread of records over the storage are allocated to the file
Question 2. Direct Access Addressing?
- The key of record is used to identify by record
- The key of record also is used to decide its storage location(or address)
1. Self addressing:
- Self addressing is a straight forwards method because a record’s address is equal
to its key’s value
- The file is inevitably stored in key sequence
• Ads of self addressing
 It leads directly to the wanted record
 No indexing or searching is required
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 The key itself need not necessarily be held within the stored
record- although it generally is
• Dis

- The search starts at the midpoint of the index and then moves half way to the left
or right(down or up) depending upon whether are wanted key is less than or
greater than the midpoint key
- In pracice, the index is unlikely to as convenient as this example because it is not
always possible to exactly halve each sucessive move(complete exact holvingis
possible only when the total number of keys in the index is 2
0
-1)
- The average number of examinations comparisons is (log
2
k)
-1
( k is the number of
keys in the index)
3. Block searching
- A block is a subdivision of an index. A block is devised to contain, roughly the
square root of the number of keys in the whole index
- The search is first through the block index to find the appropriate block and then
through this to find the wanted key
- The average number of examinations is square – root –
k
(k is the total number
of keys)
4. Balanced binary tree searching
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- A binary tree is a relationship of keys such that the examination of any key leads
to one of two other keys
- The binary tree is actually in the form of an index containing all the keys together
with a directory showing the braches stemming left and right from each key
- Binary tree searching is suitable for an unsequenced file

- They solve problems as well as or better than human experts
- They use knowledge in the form of rules or frames
- They can consider multiple hypotheses simultaneouly
• Types of ES
- An assistant
 Is the leasts expert or lowest level ESs
 It helps a decision maker by doing routine analysis and porting out
those portion of the work where human expertise is required
- A colleage
 The new discusses the problem until a joint decission is reached
 When system is going wrong, the user adds more information to
get it back on track
- True ES
 Is a system that advises the user without question
 There are no practical areas today in which decission
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