Overview of a computer system

All physical parts of the computer (or everything that we can touch) is known as hardware. All of the components of a computer system can be summarized with

the simple equations below...

Software gives "intelligence" to the computer.

Major Components of Computer System

• CPU

• Secondary Storage

• Input devices

• output devices

• communication devices

Computer Design

Basically all computers, regardless of their size, have the same general design which consist of the following

units: the central processing unit (CPU), memory, and input/output circuitry which are situated on the printed

circuit board, also called the system board or motherboard

CENTRAL PROCESSING UNIT

•The main unit inside the computer is the CPU. This unit is responsible for all events inside the computer.

•It controls all internal and external devices, performs arithmetic and logic operations. The operations a microprocessor performs are called the instruction set of this processor.

•The instruction set is "hard wired" in the CPU and determines the machine language for the CPU.

•The more complicated the instruction set is, the slower the CPU works. Processors differ from one another by the instruction set.

The CPU is composed of several units..

CPU

Control Unit

•The control unit directs and controls the activities of the internal and external devices.

•It interprets the instructions fetched into the computer, determines what data, if any, are needed, where it is stored, where to store the results of the operation, and sends the control signals to the devices involved in the execution of the instructions.

ALU

The arithmetic and logic unit (ALU) is the part where actual computations take place.

It consists of circuits which perform arithmetic operations (e.g. addition, subtraction, multiplication, division) over data received

from memory and capable to compare numbers

Registers

• While performing these operations, the ALU takes data from the temporary storage area inside the CPU named registers.

• Registers are a group of cells used for memory addressing, data manipulation and processing. Some of the registers are general purpose and some are reserved for certain functions.

• It is a high-speed memory which holds only data for immediate processing and results of this processing. I

• f these results are not needed for the next instruction, they are sent back to the main memory and registers are occupied by

the new data used in the next instruction.

Clock speed

•All activities in the computer system are composed of thousands of individual steps. These steps should follow in some order in fixed intervals of time.

•These intervals are generated by the clock unit. Every operation within

•the CPU takes place at the clock pulse. No operation, regardless of how simple, can be performed in less time than transpires between ticks of this clock.

•But some operations require more than one clock pulse. The faster the clock runs, the faster the computer performs. The clock rate is measured in megahertz (Mhz) or million ticks per second. At the moment of writing of these notes the highest clock rate is 600MHz but by the time you read them probably quicker microprocessors will be on the market. Larger systems are even faster.

•In "older" systems the clock unit is external to the microprocessor and resides on a separate chip. In most modern microprocessors the clock is usually incorporated within the CPU.

CPU Features

The two main features of the CPU are:

• its speed measured in millions of instructions per second;

• the word size

MEMORY

There are two main types of memory inside the computer

ROM

Read-only-memory (ROM) is a chip or a group of chips containing programs, tables of constants and instructions for the CPU. Only the CPU has access to this memory.

For example, when we turn on the computer, the CPU gets its first instructions from the ROM. These instructions are burnt into the chip with the help of special equipment before the chip is installed inside the computer.

Users do not have access to the ROM, so they can't change these

instructions.

RAM

Users work with the random-access-memory (RAM).

RAM is a collection of cells and we can access any cell at any

given time, hence the name random access memory.

Another name for RAM

RAM is often referred to as main memory or primary storage.

RAM usually occupies a number of chips

connected together.

It is used to store programs and data being used by these programs while the computer is

on.

When the computer is turned off any information is erased from the RAM. That is why RAM is

often called volatile while ROM is a non-volatile type of memory.

What’s Inside

Peripheral devices

Peripheral devices are devices connected to the computer but external in relation to the processing unit. If a peripheral device is disconnected, the computer will still be able to work; only functions performed by this peripheral device will not be available.

For example, if you disconnect a keyboard, you would not be able to type in information but you will be able work with the graphical user interface by clicking the mouse.

If you remove the hard disk, you will have to start up your computer using floppy disk and you will have to save your data on floppy disks only but the computer will still be working.

Peripheral devices can reside inside the computer case or outside.

For example, a mouse, a keyboard, a monitor are always outside the case and they are connected to the computer via ports which are situated on the back of the case.

Disk drives are positioned inside the case and they are connected to the motherboard via

disk controller cards which are inserted in the expansion slots on the motherboard.

Peripheral devices

Peripheral devices are classified according to the purpose they serve:

Input devices are used for data input

Output devices are used for data output

Storage devices are used to store data for long periods of time

Computer System

Let’s see what you would get if you bought a system?

Software

A computer cannot do anything without instructions.

Sets of instructions are called programs. •Programs and data are used to control the hardware of the computer system and to interface the user to a PC. •Programs and data are called software. •Whatever you want your computer to do, you give your instructions using software.

Software is usually classified as system

software and application software.

The most important system software is an operating system.

•An operating system is a set of programs responsible for monitoring sequences of events in the computer system, controlling the resources of the computer system (e.g. distribution of memory and handling peripheral devices) and supporting communications between the elements making up the computer system.

•You can consider an operating system as an interpreter

Classifications of softwareThe table below classifies software and gives examples for each group.

Software, system, application Operating Systems Word Processors Spreadsheets utilities

MS-DOS Word Excel Norton Utilities

Windows 95 Word Perfect Lotus 1-2-3 Virua Buster

Windows NT Ami Pro Quatro Pro Virus Scan

MacOS (e.g. System 7)

UNIX Databases

VAX/VMS dBASE

Windows 3.x Access

LapLink FileMaker

Finder Paint/Draw Games

Paint Shop Pro Solitaire

Corel Photo Paint Minesweeper

Corel Draw

Programming Languages

•Another type of software is programming languages.

•Programming languages are used to create all other software whether it is system or application software.

•Modern programming environments have graphical user

interfaces (GUI) featuring symbolic icons and drag-and-drop technique and English-like statements. Delphi and Visual Basic are the most popular examples of such environments.

•Programming in visual environment creates an impression that it is very easy to write programs. But becoming a good programmer requires talent,

ability to learn, logic, creativity, patience and experience.

Software: open and proprietary

Software can be categorized as open system or proprietary.

Open System

•Open system software can be modified for use with any hardware. •It is not the exclusive property or design

of a particular vendor. For example, UNIX is the first operating system that works on minicomputers, mainframes and PCs. Its inner workings are available to the public and anyone can adapt it or develop

applications to work with it.

Proprietary system

• The proprietary products are designed for particular systems and cannot be used with other hardware.

• Its inner workings are protected information. • For example, Apple computers and software for

them have been proprietary products for many years. Only recently Apple licensed its MacOS to other hardware companies to build Macintosh clones.

Factors That Influence Personal Computers Performance

1.The CPU.

2.Clock rate.

3.RAM

4.Cache presence and size.

5.Data bus type and size.

6.Hard disk capacity and seek time.

7.Videocard.

8.CD-ROM drive speed.

9.MMX processors.

Figure 1. The memory banks where memory chips will be

installed.

Half ram and full ram

Let’s look at a few ads

Can you identify what these parts are?

• What is each part?

• Can you identify each part on a quiz?

Additional resources

http://mentor.coe.uwf.edu/2040c/basics/sld001.htm

MOTHERBOARD

• The motherboard is probably the most important part of your computer. If the CPU is the brains then the motherboard is the backbone. Without the motherboard absolutely nothing can happen.

• The motherboard manages all the movement of bytes, bits and data flow between the CPU, memory and any peripherals attached.

• The motherboard holds the CPU its cache, the I/O chips, all the memory, disk drives, PCI, ISA, AGP cards and the BIOS (Basic input/output system).

• Choosing the right motherboard can be a headache inducing experience. The main factors in choosing a motherboard would be your need for speed, and what you can

afford.

Motherboard Resources

http://www.sysopt.com/mboard.html

Types of Hardware

• Various Types of Hardware

Input

Output

Storage

Processing

Some things to remember

• 1.The CPU.

High performance, compatibility and upgradability are features that are important. The higher the generation, the better

Keep on ticking

2.Clock rate.

Since any step of processing can happen only on the "tick" of the clock (called clock cycle), the faster the rate the quicker the CPU works. The Pentium processors have the ability to execute multiple instructions per clock cycle due to the fact that the Pentium processor's two pipelines can execute two instructions simultaneously. If other modules of the system require more than one clock pulse, the CPU has to wait for them to keep up. This is called a wait state.

Ram it!

3.RAM.

It does not make much sense to have a fast processor if you don’t have fast RAM

The benefits of

adding more RAM include letting you open more applications at the same time, and working with large

files or documents. More memory may also make your

machine run much faster.

Chips, anyone?

The quality of DRAM chips used in a memory module is the most important component in

determining

the overall quality and reliability of RAM. So which chips to consider?

L1 Cache vs. L2 Cache

Enhanced Data Output (EDO) DRAM provides faster data throughput.

Systems using EDO DRAM will be faster than similar systems using regular DRAM.

EDO DRAM provides even higher performance benefit when used with an L2 cache.

EDRAM

Enhanced DRAM (EDRAM) can be thought of as RAM that carries its own cache on each module.

•In an EDRAM-based system, essentially the entire system memory bank is the cache. This can

provide dramatic performance improvements.

•Very Expensive

Cache, anyone?

• 4.Cache presence and size.• L1 Cache.

The bigger the on-chip cache size, the better since more instructions and data can be stored on the chip, reducing the number of times the processor has to access slower, off-chip memory areas to get data.

• For example, Intel has doubled on-chip cache size to 32K on the Intel Pentium processor with MMX

technology.

L2 Cache

L2 Cache.

System memories composed of dynamic RAM (DRAM) alone have not been able to keep up with the dramatic increases in CPU speeds over the years.

In order to optimize the memory performance in these systems, designers are implementing architectures using cache memory, resulting in speed increases up to 45%.

Expanding secondary cache (e.g. from 128K to 512K) can greatly

improve the performance of some applications.

The road more or less traveled

• 5. Data bus type and size.

• The data bus is the highway that carries information between the processor and the memory subsystem.

• The wider the data bus, the more information it can transfer• The PCI local bus greatly improves I/O performance. It can transfer data between

the processor and the peripherals at up to 132 MB/second, far faster than the ISA bus rate of 5 MB/second.

In-class group projects

To be announced.

Multimedia needs higher performance capacity!

6.Hard disk capacity and seek time.

In the early - mid 90s, High-performance hard drives with at least 1.2 G of capacity, provided an average seek time of 12 milliseconds, a 128 to 256 K hard disk buffer cache with both write-caching and read-caching capabilities, and spin about 4,500 rotations per minute

Now, we are looking at using high performance hard drives with 10 G of capacity or better!

Video, Sound, and Speed

7.Videocard.

8.CD-ROM drive speed.

9.MMX processors

MMX?

• Multimedia extensions processors (MMX) is designed specifically to support media-rich software and communications applications..

• The Pentium processor with MMX technology will give a better,

smoother and more realistic multimedia experience.

• These processors have got 57 powerful new instructions specifically designed to manipulate and process video, audio and graphical data efficiently.

• However, your system will require software designed for MMX technology (old software must be recompiled to take advantage of new MMX features).

Types of RAM

There are different types of RAM used for different purposes.

They include: DRAM, FPM DRAM, EDO, RAM, SDRAM, SRAM, EDRAM, VRAM, WRAM and

RDRAM

DRAM

• Dynamic Random Access Memory, or DRAM is the most common type of memory chip. DRAM chips are the Integrated Circuits, or ICs, positioned on a small Printed Circuit Board, or PCB.

• They come in many capacities (usually 1, 2, 4, 8, 16 or 32 M) on the same PCB, and install easily in special slots on the system

• board. (Older computers may use socketed chips or may not be expandable at all.) It is inexpensive. but slow

• so if you can afford more expensive memory go for EDO RAM.

EDO Memory

Extended Data Output, or EDO RAM, is one of a series of recent innovations in DRAM chip technology.

On computer systems designed to support it, EDO memory allows a CPU to access memory 10 to 15

percent faster than comparable fast-page mode chips.

Synchronous DRAM

•Synchronous DRAM, or SDRAM, is a new DRAM technology that uses a clock to synchronize signal input and output on a memory chip.

•The clock is coordinated with the CPU clock so the timing of the memory chips and the timing of the CPU are in 'synch'.

•Synchronous DRAM saves time in executing commands and transmitting data, thereby increasing the overall performance of the computer.

See Table

Pay attention to the table on the types of RAM