The document provides an overview of computer system hardware, focusing on the central processing unit (CPU), memory units (RAM and ROM), and instruction formats and cycles. It contrasts RISC (Reduced Instruction Set Computer) and CISC (Complex Instruction Set Computer) architectures, discussing their features, advantages, and differences in instruction handling. Additionally, it describes the roles of buses in data transfer between computer components and the basic structure of modern computers.

1. The Computer System Hardware
Apart From Computer Software
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2. Introduction
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3. Central Processing Unit
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4. Memory Unit
 They are internal storage areas in a computer
 In the form of chips
 Two Categories : RAM and ROM
RAM (Random Access Memory):
 Holds the data as long as electric supply is on. (volatile).
 Two Basic Types
i) Dynamic RAM : needs to be refreshed
ii) Static RAM : less often refreshed, expensive
ROM (Read Only Memory):
 Non-Volatile
 Program stored in ROM is FIRMWARE programed by manufacturer.
 Eg. Program that boots the computers are stored here.
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5. Instruction Format
 An Instruction is normally made up of a combination if an operation
code and some way of specifying an operand, most commonly by its
location or address in memory.
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6. Instruction Set
FEW EXAMPLES
ADD - Add two numbers together. || ADD R4, R3 :: R4  R4 + R3
COMPARE - Compare numbers.
IN - Input information from a device, e.g. keyboard.
JUMP - Jump to designated RAM address.
JUMP IF - Conditional statement that jumps to a designated RAM address.
LOAD - Load information from RAM to the CPU.
OUT - Output information to device, e.g. monitor.
STORE - Store information to RAM.
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7. Instruction Cycle
 Sometimes called fetch decode cycle.
 It is basic operational process of computer in which a computer retrieves
a program instruction from its memory that determines what actions the
instruction indicates and carries out those action.
 FETCH  DECODE  EXECUTE
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8. Instruction Cycle
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9. Microprocessor
 Incorporates the functions of a computer’s Central Processing Unit
(CPU) on a single Integrated Circuit (IC).
 Intel, atmel, hp, ARM, NVIDIA,
 Illustration of Example from TextBook.
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10. Interconnection : Buses
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11. Interconnection : Buses
 BUS is a set of electronic signal pathway that allows information and
signals to travel between components inside or outside of a computer.
 The different components of computer i.e. CPU, I/O and MU are
connected each other by a bus.
 The data, instructions and the signals are carried between the different
components via a bus.
 The command to access the memory or the I/O is carried by a control
bus.
 The address of I/O device or memory is carried by a address bus.
 The data to be transferred is carried by the data bus.
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12. Inside a Computer Cabinet
 Modern Computer Consist of three basic section:
 A Processor
 Some Memory
 I/O (Peripheral) Devices
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13. Before RISC Vs CISC
Speeding Up
 Memory Mapped I/O
 I/O Processors
 Memory Cache
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14. RISC Vs CISC
RISC – Reduced Instruction Set Computer
 Less Space and Shorter design cycle.
 Use of pipelining for immense processing power.
Advantages:
 Speed : Due to simplified instruction
 Simpler Hardware : Less Chip space
 Shorter Design Cycle : Short Machine Cycle.
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15. RISC Vs CISC
CISC – Complex Instruction Set Computer
 Uses Microcode.
 Build Rich instruction set and Build high-level instruction set.
Features:
 Several special purpose registers
 Few general purpose registers.
 Single instruction to support multiple addressing mode.
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16. An Ideal CISC Machine
 An instruction is fetched from the memory
 The instruction is decoded.
 The instruction is executed
 The results are written in the memory.
CISC Processors are designed to execute instruction completely before
beginning the next instruction :: No PIPELINING
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17. Instruction Pipelining
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18. Example (RISC/CISC)
LOAD R1, A
LOAD R2,B
PROD A, B
STORE R3, A
MULT A,B  In CISC (One Complex instruction)
 In RISC (Number of fewer simple instruction)
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19. Thanks!
Er. Sharad Kafle
Institute of Engineering, Tribhuwan University
Web : www.skafle.com.np
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