Faculty Of Engineering and Technology

Department of Computer Science

Course: Introduction to IT
Course Code : CS- 104
(Lecture-6)

Lecturer: Nazir Ahmad Qayoom

Department: Computer Science
Email: n.qayoom@kardan.edu.af
Mobile: +93(0) 706338869
 CONTENTS

• CPU Architecture

• Machine Cycle

• Word size

• Cache Memory

• Buses

2
 OUTCOMES

At the end of this lecture, students will be able to;

• CPU Architecture

• Machine Cycle

• Word size

• Cache Memory

• Buses

3
 System Unit: CPU Architecture

• Two components handle processing in a computer:

• The central processing unit Or CPU

• The memory

• Both are located on the computer’s motherboard.

 Machine Cycle

• The Machine cycle is the main activity of the CPU to execute the program
instructions.
• CPU continuously performs the Machine cycle necessary for program execution.
• It is also called as Instruction cycle, CPU cycle, Processor cycle.
• It includes four steps accordingly:
1. Fetch
2. Decode
3. Execute
4. Store
 Cache Memory

• It is the fastest and Closest memory inside or outside of the processor.

• When the processor need any data to complete the currently running process, so the
processor will first search the data in the cache memory, if not available then will
search the data in the RAM.
• Cache have important role in the Speed of Computer.
 Cache Memory

• Moving data between RAM and the CPU’s registers is one of the most time
consuming operations a CPU must perform, simply because RAM is much slower
than the CPU.

• A partial solution to this problem is to include a cache memory in the CPU.

• Cache memory is a very high speed memory which can speed up the CPU. It acts as a
buffer between the CPU and the main memory. It is used to hold the intermediate
result.
 Cache Memory

• It has many levels:

• Level 1 cache
• Level 2 cache
• Level 3 cache.

• L1 Cache:
• L1 cache is built directly in the processor chip. L1 cache usually has a very small
capacity, ranging from 8 KB to 128 KB.
 Cache Memory

• L2 Cache:
• L2 cache is slightly slower than L1 cache but has a much larger capacity, ranging from
64 KB to 16 MB.
• Current processors include advanced transfer cache, a type of L2 cache built directly
on the processor chip.
• Processors that use advanced transfer cache perform at much faster rates than those
that do not use it.
• Personal computers today typically have from 512 KB to 12 MB of advanced transfer
cache.
 Cache Memory

• Cache speeds up processing time because it stores frequently used instructions and data.

• When the processor needs an instruction or data, it searches memory in this order: L1
cache, then L2 cache, then RAM — with a greater delay in processing for each level of
memory it must search.

• If the instruction or data is not found in memory, then it must search a slower speed
storage medium such as a hard disk or optical disc.
 Word size

• Register:

• Register is a small high speed memory inside CPU.

• It is used to store data and instructions temporary.
• Data is stored in register from main memory for execution.
• CPU contains a number of registers. Each register has a predefined function
• Register size determine how much information it can store.
 Word size

• "Word size" refers to the number of bits processed by a computer's CPU in one implement
(these days, typically 32 bits or 64 bits).

• The register in the first PCs could hold two bytes-16 bits-each.

• Most CPUs sold today, have 64-bits registers.

• The size of the register, which is sometimes word size, indicates the amount of data with
computer can work at any given time.

• The bigger the word size, the more quickly the computer can process a set of data.

• 32-bit, 64-bit and 128-bit processors refers to the size of the registers in the processor.
 Word size

• The register in the first PCs could hold two bytes-16 bits-each.

• Most CPUs sold today, have 64-bits registers.

• The size of the register, which is sometimes word size, indicates the amount of data
with computer can work at any given time.

• The bigger the word size, the more quickly the computer can process a set of data.

• 32-bit, 64-bit and 128-bit processors refers to the size of the registers in the processor.
Word size
 Bus

• A Bus is a path between the components of a computer. There are two main buses in a
computer: the internal(or system) bus and the external(or expansion) bus.

• The system buses resides on the motherboard and connects the CPU to other devices
that resides on the motherboard.

• An expansion bus connects external devices, such as the keyboard, mouse, modem,
printer, and so on, to the CPU. Cables from disk drives and other internal devices are
plugged into the bus.

• The system bus has two Categories': the data bus and the address bus.
Bus
Bus
Bus
Thank You…!