Lect 1

System Concept A system is a group of integrated parts which have common purpose of achieving some objectives. The key characteristics are: – A system has more than one element. – All the elements of a system are logically related. – All the elements of a system are controlled in a manner to achieve the system goal.

Program & Data Input Unit

Storage Unit Secondary Storage Primary Storage

Output Unit Information

Control Unit Arithmetic Logic Unit Central Processing Unit

Basic Organization of a Computer System

Functions performed by Input Unit It accepts the instructions and data from the outside world. It converts these instructions and data in computer acceptable form. It supplies the converted instructions and data to the computer system for further processing. Summarizing – Cause an input device to physically read data. – Transmit the data from the input device to an input area of the CPU.

Functions performed by Output Unit It accepts the results produced by the computer, which are in coded form, and hence, cannot be easily understood by us. It converts these coded results to human acceptable form It supplies the converted results to the outside world.

Storage Unit Specific Functions are to hold – The data and instructions required for processing (received from input devices) – Intermediate results of processing – Final results of processing, before these results are released to an output device.

Primary Storage Secondary Storage

Central Processing Unit (CPU) Brain of the computer. Data is manipulated. At times there are multiple CPU’s in a single system. 1St processor was the Intel 4004, Only Add n Subtract 4 Bits. Introduced in 1971

PC

CPUs

Year

No. of Transistors

1st Gen

8086, 8088

1978-81

29,000

2nd Gen

80286

1984

134,000

3rd Gen

80386

1987-88

275,000

4th Gen

80486

1990-92

1,200,000

1993-95 1996 1996 1997 1997 1998

3,100,000

5th Gen

Pentium, Cyrix 6x86, AMD K5 Improved Pentium MMX, 5th Gen IBM/Cyrix 6x86MX, IDT Winchip2 3D

3,500,000 4,500,000 6,000,000 6,000,000

Basic Components of CPU Primary Storage Output

Input

Control Unit

ALU

CPU

How does CPU work? CPU is centrally located on the motherboard. It continually receives instructions to be executed. The work mostly consists of calculations and data transport. Data to be processed

The CPU

Processed Data

Data have a path to the CPU. Data expressway  System bus

The CPU

The System Bus

The RAM

CPU receives at least two types of data: – Instructions on how to handle the other data. (Program Code) – Data, which must be handled according to the instructions (User Data)

The Other Units

Types of CPU Memory Magnetic Core Memory – doughnut shaped ferrite elements. – Clockwise – Anticlockwise.

Integrated Circuits – made from semiconductors – Two types : bipolar and metal oxide semiconductor.

Charge-Coupled Devices (CCD) – High Speed Memories with large capacities at a relatively low cost.

Magnetic Bubble Memory – Consists of magnetized spots on a thin film of semiconductor material. – Non-volatile.

The ROM Chip ROM code holds start-up instructions Connects to various hardware peripherals Connects to CMOS instructions Setup Program

BIOS Program Calls OS

POST Routines

Boot Instructions

ROM Chip

Inside a CPU A microprocessor executes a collection of machine instructions that tell the processor what to do. Using its ALU (Arithmetic/Logic Unit), a microprocessor can perform mathematical and logical operations A microprocessor can move data from one memory location to another. A microprocessor can make decisions and jump to a new set of instructions based on those decisions.

CPU

This is about as simple as a microprocessor gets. This microprocessor has: An address bus (that may be 8, 16 or 32 bits wide) that sends an address to memory A data bus (that may be 8, 16 or 32 bits wide) that can send data to memory or receive data from memory An RD (read) and WR (write) line to tell the memory whether it wants to set or get the addressed location A clock line that lets a clock pulse sequence the processor A reset line that resets the program counter to zero (or whatever) and restarts

Machine Cycles Each time the CPU executes an instruction, it takes a series of steps. The completed series of steps is called a machine cycle. Machine Cycle

Instruction Cycle

Fetching

Decoding

Execution Cycle

Executing

Storing

Arithmetic Logical Unit (ALU) The ALU mainly performs two types of operations. Mathematical – Add(+), Subtract(-), Multiply(*), Divide(/) and Raise by a power (^) Logical – Equal to OR not equal to, Greater than OR not greater than, less than or not less than, greater than or equal to, not greater than or equal to, less than or equal to, not greater than or equal to. When the instruction decoder encounters any instruction that involves arithmetic or logical operation it passes it to the ALU. It includes high speed registers used to hold data currently being processed. Size of register determines amount of data the computer can work on at any given time.

ROM – Read Only Memory Also known as firmware Data stored in these chips is nonvolatile - it is not lost when power is removed. Data stored in these chips is either unchangeable or requires a special operation to change BIOS - basic input/output system of your computer are saved in the ROM. It Contains startup instruction

ROM types There are four basic ROM types: ROM – Read only Memory (Non Volatile) PROM – Programmable ROM EPROM – Erasable Programmable ROM EEPROM – Electrically Erasable Programmable ROM

RAM – Random Access Memory Volatile memory requires power to store data. Any memory cell can be accessed randomly if row n column of memory cell known. If power is removed all data stored on RAM is lost. Make processing time very fast. Cheapest way to make your PC faster

RAM working In Dynamic RAM a memory cell consists of a capacitor and a transistor (Switch) A memory cell’s charge is lost in a few milliseconds hence needs to be refreshed by the CPU or memory controller. Saves data that is most frequently accessed by CPU. Improves speed of computer by minimizing access time of frequently used data.

Cache Caching is a technology based on the memory subsystem of your computer. The main purpose of a cache is to accelerate your computer while keeping the price of the computer low. Caching allows you to do your computer tasks more rapidly. L1 cache – cache onboard the microprocessor, smallest in size and access time is smallest too. Most expensive. L2 cache – Earlier this cache was onboard the mother board and access speed was faster than RAM but slower than L1 cache. Size larger than L1 cache. L3 cache – Now L2 cache also has been included into the microprocessor giving birth to L3 cache as onboard the motherboard.

DATA & ADDRESS BUS DATA – transfers data to & from CPU to other devices. Size of bus can be 16Bit, 32Bit & now a days 64Bit. Speed of bus is another important criteria. Mostly the speed of the bus is a multiple of the processor speed. E.g.. 400Mhz in a 1.6Ghz processor. Earlier speeds use to be only 100-133Mhz. Now a days speeds go up to 800Mhz & even higher. ADDRESS – similar to the Data bus it only connects the CPU to the RAM and only carries memory addresses. Note each byte of RAM is associated with a number, which is the memory address.

BUS Standards ISA – Industry Standard Architecture, 16Bit, released in mid 1980’s, still used to connect slow devices. PCI – Peripheral Component Interconnection, designed by Intel to make it easier to integrate new data types’ such as audio, video & graphics. AGP – Accelerated Graphics Port, Allows video cards to access system RAM, greatly increases speed of graphics performance. USB – Universal Serial Port, Hot swap, up to 127 device connection in daisy chain or hub layout. IEEE 1934 – (Fire Wire), very fast data transfer but expensive, used mainly for video & TV connection. PC Data Card – to attach external devices such as WiFi, modems, Thumb scanner etc.