This document provides an overview of core hardware components and PC maintenance. It discusses external data buses, CPU registers like the program counter and accumulator, computer memory types, and the Intel 8086 and 80286 CPU families. Registers are used to store small amounts of data during processing. Memory can be volatile RAM or non-volatile ROM. The 8086 was a 16-bit processor that could address 1MB of memory, while the 80286 had improvements like a non-multiplexed bus and faster performance.

1. Lecture 4
Core Hardware and PC Maintenance

2. Outline
• External Data Bus
• Registers
• Memory
• 8086 CPU Family
• 80286 CPU Family

3. External Data Bus
• An external bus primarily enables connecting peripherals
and all external devices to a computer. These devices can
include storage, monitors, keyboard, mouse and more.
• Typically, an external bus is composed of electrical
circuits that connect and transmit data between the
computer and the external device. Being external to the
computer, external buses are much slower than internal
buses. Moreover, an external bus can be both serial or
parallel.
• Universal Serial Bus (USB) , PCI (Peripheral Component
Interconnect) bus and IEEE 1294 are common examples
of external buses.

4. Registers
• Registers are small amounts of high-speed memory
contained within the CPU. They are used by the
processor to store small amounts of data that are
needed during processing, such as:
• the address of the next instruction to be executed
• the current instruction being decoded
• the results of calculations

5. Registers Cont...
• Different processors have different numbers of
registers for different purposes, but most have
some, or all, of the following:
• program counter (PC)
• memory address register (MAR)
• memory data register (MDR)
• current instruction register (CIR)
• accumulator (ACC)

6. Registers Cont.…
• A program counter (PC) is a CPU register in the computer processor which has the
address of the next instruction to be executed from memory.
• memory address register (MAR) - holds the address of the current instruction that
is to be fetched from memory.
• memory data register (MDR) - holds the contents found at the address held in the
MAR, or data which is to be transferred to primary memory.
• CIR - An instruction register holds a machine instruction that is currently being
executed.
• This Register is used for storing the Results those are produced by the System.
When the CPU will generate Some Results after the Processing then all the Results
will be Stored into the AC Register.

7. Memory
• Computer memory is any physical device capable of storing
information temporarily, like RAM (random access memory), or
permanently, like ROM (read-only memory).
• Memory can be either volatile and non-volatile memory.
• Volatile memory is memory that loses its contents when the
computer or hardware device loses power. Computer RAM is an
example of volatile memory. It is why if your computer freezes or
reboots when working on a program, you lose anything that hasn't
been saved.
• Non-volatile memory, sometimes abbreviated as NVRAM, is memory
that keeps its contents even if the power is lost. EPROM is an
example of non-volatile memory.

8. Memory Cont.…
• It is very common for new computer users to be
confused by what parts in the computer are
memory. Although both the hard drive and
RAM are memory, it's more appropriate to refer
to RAM as "memory" or "primary memory" and
a hard drive as "storage" or "secondary
storage."

9. Memory Cont.…
• How is memory used?
When a program, such as your Internet browser, is open, it is loaded
from your hard drive and placed into RAM. This process allows that
program to communicate with the processor at higher speeds. Anything
you save to your computer, such as a picture or video, is sent to your
hard drive for storage.

10. Intel 8086
• Intel 8086 microprocessor is the enhanced version of Intel 8085
microprocessor. It was designed by Intel in 1976.
• The 8086 microprocessor is a16-bit, N-channel, HMOS
microprocessor. Where the HMOS is used for "High-speed Metal
Oxide Semiconductor".
• Intel 8086 is built on a single semiconductor chip and packaged in
a 40-pin IC package. The type of package is DIP (Dual Inline
Package).
• Intel 8086 uses 20 address lines and 16 data- lines. It can directly
address up to 220 = 1 Mbyte of memory.
• It consists of a powerful instruction set, which provides operation
like division and multiplication very quickly.
• 8086 is designed to operate in two modes, i.e., Minimum and
Maximum mode.

11. 80286 CPU Family
• 80286 Microprocessor is a 16-bit microprocessor that has the
ability to execute 16-bit instruction at a time. It has non-
multiplexed data and address bus. The size of data bus is 16-
bit whereas the size of address bus is 24-bit.
• It was invented in February 1982 by Intel. 80286
microprocessor was basically an advancement of 8086
microprocessor. Further in 1985, Intel produced upgraded
version of 80286 which was a 32-bit microprocessor.

12. 80286 CPU Family Cont.…
• Now the question arises what are the factors that make
80286 more advantageous than 8086 microprocessor?
• It has non-multiplexed address and data bus that reduces
operational speed.
• The addressable memory in case of 80286 is 16 MB.
• It offers an additional adder for address calculation.
• 80286 has faster multipliers that lead to quick operation.
• The performance per clock cycle of 80286 is almost twice when
compared with 8086 or 8088.