It notes given by mam

1.  Registers hold data that can be readily accessed by
the CPU.
 They can be implemented using D flip-flops.
◦ A 32-bit register requires 32 D flip-flops.
 The arithmetic-logic unit (ALU) carries out logical and
arithmetic operations as directed by the control unit.
 The control unit determines which actions to carry out
according to the values in a program counter register
and a status register.
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2.  Buses consist of data lines, control lines, and
address lines.
 While the data lines convey bits from one device to
another, control lines determine the direction of data
flow, and when each device can access the bus.
 Address lines determine the location of the source
or destination of the data.
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The next slide shows a model bus configuration.

3. 3

4.  Every computer contains at least one clock that
synchronizes the activities of its components.
 A fixed number of clock cycles are required to carry
out each data movement or computational operation.
 The clock frequency, measured in megahertz or
gigahertz, determines the speed with which all
operations are carried out.
 Clock cycle time is the reciprocal of clock frequency.
◦ An 800 MHz clock has a cycle time of 1.25 ns.
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5.  A computer communicates with the outside world
through its input/output (I/O) subsystem.
 I/O devices connect to the CPU through various
interfaces.
 I/O can be memory-mapped-- where the I/O device
behaves like main memory from the CPU’s point of
view.
 Or I/O can be instruction-based, where the CPU has
a specialized I/O instruction set.
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6.  Computer memory consists of a linear array of
addressable storage cells that are similar to registers.
 Memory can be byte-addressable, or word-
addressable, where a word typically consists of two or
more bytes.
 Memory is constructed of RAM chips, often referred
to in terms of length  width.
 If the memory word size of the machine is 16 bits,
then a 4M  16 RAM chip gives us 4 megabytes of
16-bit memory locations.
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7.  How does the computer access a memory location
corresponds to a particular address?
 We observe that 4M can be expressed as 2 2  2 20
= 2 22 words.
 The memory locations for this memory are
numbered 0 through 2 22 -1.
 Thus, the memory bus of this system requires at
least 22 address lines.
◦ The address lines “count” from 0 to 222 - 1 in
binary. Each line is either “on” or “off” indicating
the location of the desired memory element.
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8.  The normal execution of a program is altered when
an event of higher-priority occurs. The CPU is
alerted to such an event through an interrupt.
 Interrupts can be triggered by I/O requests,
arithmetic errors (such as division by zero), or when
an invalid instruction is encountered.
 Each interrupt is associated with a procedure that
directs the actions of the CPU when an interrupt
occurs.
◦ Nonmaskable interrupts are high-priority
interrupts that cannot be ignored.
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9. seven registers are:
• Accumulator, AC, a 16-bit register that holds a
conditional operator (e.g., "less than") or one operand
of a two-operand instruction.
• Memory address register, MAR, a 12-bit register that
holds the memory address of an instruction or the
operand of an instruction.
• Memory buffer register, MBR, a 16-bit register that
holds the data after its retrieval from, or before its
placement in memory.
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10. seven registers are:
• Program counter, PC, a 12-bit register that holds the
address of the next program instruction to be executed.
• Instruction register, IR, which holds an instruction
immediately preceding its execution.
• Input register, InREG, an 8-bit register that holds data
read from an input device.
• Output register, OutREG, an 8-bit register, that holds
data that is ready for the output device.
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11. A computer goes through the following
instruction cycle repeatedly:
do
1. Fetch an instruction from memory
2. Decode the instruction
3. Read the effective address from memory
if the instruction has an indirect address
4. Execute the instruction until a HALT
instruction is encountered
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12.  The fetch-decode-execute cycle is the series of steps
that a computer carries out when it runs a program.
 We first have to fetch an instruction from memory,
and place it into the IR.
 Once in the IR, it is decoded to determine what
needs to be done next.
 If a memory value (operand) is involved in the
operation, it is retrieved and placed into the MBR.
 With everything in place, the instruction is executed.
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The next slide shows a flowchart of this process.

13. 13

14.  All computers provide a way of interrupting the
fetch-decode-execute cycle.
 Interrupts occur when:
◦ A user break (e.,g., Control+C) is issued
◦ I/O is requested by the user or a program
◦ A critical error occurs
 Interrupts can be caused by hardware or
software.
◦ Software interrupts are also called traps.
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15.  Interrupt processing involves adding another step to
the fetch-decode-execute cycle as shown below.
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The next slide shows a flowchart of “Process the interrupt.”

16. 16

17.  For general-purpose systems, it is common to
disable all interrupts during the time in which an
interrupt is being processed.
◦ Typically, this is achieved by setting a bit in the
flags register.
 Interrupts that are ignored in this case are called
maskable.
 Nonmaskable interrupts are those interrupts that
must be processed in order to keep the system in
a stable condition.
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19.  Computer Instructions or data, anything that can
be stored electronically is Software.
 Hardware is one that is tangible. The storage
devices (Hard disk, CD’s etc.,), mouse, keyboard
CPU and display devices (Monitor) are Hardware.
For example: There is a problem in the Software
implies – Problem with program or data

20. System Software
Application Software

21. System Software includes the Operating System and all
the utilities that enable the computer to function.
 Are a set of programs which are meant not only for the
computer operation but also for the effective utilization
of the computer hardware.
 In other words system software are a set of program
which are used for controlling the computer hardware
and for interfacing, interconnecting the various
resources of computer system in an optimal way.
Example:
Operating Systems, Compiler, Loader, Linker,
Interpreter.

22. A set of program comprising various modules
that are written for specific application
Application Software includes programs that do real
work for user.
Example:
Payroll systems, Inventory Control, Manage
student database, Word Processor, Spreadsheet
and Database Management System etc.,

23. Operating System:
 Operating System is a software, which makes a
computer to actually work.
 It is the software the enables all the programs we
use.
 The OS organizes and controls the hardware.
 OS acts as an interface between the application
programs and the machine hardware.
 Examples: Windows, Linux, Unix and Mac OS, etc.,

24. Source
Languages
Target Languages
‘C’ language ‘C’ language
‘Pascal’ language Machine language
FORTRAN language
C++ language
ADA language
Compiler: A compiler is a program that reads a program in one
language – the source language and translates into an equivalent
program in another language – the target language.

25. Loader: A loader is the part of an operating system
that is responsible for loading programs into
memory, preparing them for execution and then
executing them.
The loader is usually a part of the operating
system's kernel and usually is loaded at system
boot time and stays in memory until the system is
rebooted, shut down, or powered off.

26. Linker: A linker or link editor is a program that
takes one or more objects generated by compilers
and assembles them into a single executable
program.
Linkers can take objects from a collection called a
library. The objects are program modules
containing machine code and information for the
linker.
The linker takes care of arranging the objects in a
program's address space.

27. Interpreter: An interpreter is a computer
program that translates and executes
instructions written in a computer
programming language line-by-line, unit by
unit etc.,
An interpreter needs to be able to analyze,
or parse, instructions written in the source
language.
Example: Lisp systems, etc.,

28. Word Processors:
Word processing is a tool that helps user in
creating, editing, and printing documents. Word
processors will normally have the following
capabilities built into them:
 Spell checking
 Standard layouts for normal documents
 Have some characters appear in bold print,
italics, or underlined
 Center lines, make text line up on the left
side of the paper, or the right side of the
paper
 Save the document so it can be used again
 print the document.
Examples: WordPerfect and Microsoft Word

29. Spreadsheets: The spreadsheet packages are
designed to use numbers and formulas to do
calculations with ease. Examples of spreadsheets
include:
 Budgets
 Payrolls
 Grade Calculations
 Address Lists
The most commonly used spreadsheet programs
are Microsoft Excel and Lotus 123.

30. Graphic Presentations: The presentation
programs can make giving presentations and using
overheads easier. Other uses include:
 Slide Shows
 Repeating Computer Presentations on a
computer monitor
 Using Sound and animation in slide shows
The most recognized graphic presentation
programs are Microsoft PowerPoint and Harvard
Graphics.

31.  CPU logic is usually faster than main memory
access time, with the result that processing speed
is limited primarily by the speed of main memory
 The cache is used for storing segments of
programs currently being executed in the CPU and
temporary data frequently needed in the present
calculations
 The typical access time ratio between cache and
main memory is about 1to7
 Auxiliary memory access time is usually 1000 times
that of main memory

33.  Most of the main memory in a general
purpose computer is made up of RAM
integrated circuits chips, but a portion of
the memory may be constructed with ROM
chips
 RAM– Random Access memory
◦ Integated RAM are available in two possible
operating modes, Static and Dynamic
 ROM– Read Only memory

34. 
Read/write memory, that initially doesn’t contain any data
 The computing system that it is used in usually stores data at
various locations to retrieve it latter from these locations

Its data pins are bidirectional (data can flow into or out of the
chip via these pins), as opposite to those of ROM that are
output only

It loses its data once the power is removed, so it is a volatile
memory
 It has a directional select signal R/W’; When R/W’=1, the chip
outputs data to the rest of the circuit; when R/W’ = 0 it inputs
data from the rest of the circuit

35.  Static RAM (SRAM)
◦ Each cell stores bit with a six-transistor (Diode) circuit.
◦ Retains value indefinitely, as long as it is kept powered.
◦ Relatively insensitive to disturbances such as electrical noise.
◦ Faster and more expensive than DRAM.
 Dynamic RAM (DRAM)
◦ Each cell stores bit with a capacitor and transistor.
◦ Value must be refreshed every 10-100 ms.
◦ Sensitive to disturbances.
◦ Slower and cheaper than SRAM.

36.  ROM is used for storing programs that are
PERMENTLY resident in the computer and
for tables of constants that do not change
in value once the production of the
computer is completed
 The ROM portion of main memory is needed
for storing an initial program called
bootstrap loader, witch is to start the
computer software operating when power is
turned off

37.  Masked ROM – programmed with its data when the chip is fabricated
 PROM – programmable ROM, by the user using a standard PROM programmer, by
burning some special type of fuses. Once programmed will not be possible to program
it again

EPROM – erasable ROM; the chip can be erased and chip reprogrammed; programming
process consists in charging some internal capacitors; the UV light (method of erase)
makes those capacitors to leak their charge, thus resetting the chip
 EEPROM – Electrically Erasable PROM; it is possible to modify individual locations of the
memory, leaving others unchanged; one common use of the EEPROM is in BIOS of
personal computers.

38. 
DRAM and SRAM are volatile memories

Lose information if powered off.
 Nonvolatile memories retain value even if powered off.

Generic name is read-only memory (ROM).

Misleading because some ROMs can be read and modified.
 Types of ROMs

Programmable ROM (PROM)

Eraseable programmable ROM (EPROM)

Electrically eraseable PROM (EEPROM)

Flash memory

39.  The main memory construction is costly. Therefore, it has
to be limited in size. The main memory is used to store only
those instructions and data which are to be used
immediately. However, a computer has to store a large
amount of information. The bulk of information is stored in
the auxiliary memory. This is also called backing storageor
secondary storage. They include hard disk, floppy
disks, CD-ROM, USB flash drives, etc.
 When the electricity supply to the computer is off, all data
stored in the primary storage is destroyed. On the other
hand, this is not true for secondary storage. The data stored
in secondary storage can be stored for the desired time.

40.  Firmware:-
It is pre-written program in machine language
that is stored in ROM (Read Only Memory).
Example:-BIOS.Firmware boots up computerized
devices.
 Humanware:-
The personnel which are related to installation,
maintenance, operation and testing of computer
are called humanware.
Example:-Programmer, Hardware/Network
Engineers, System Analysts
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