Types of Computers

Mainframe/Server

• Two Dual-Core Intel® Xeon® Processors 5140

• Multi user access

• Large amount of RAM (48GB) and Backing Storage

Desktop

• Single user access

• 1 Gb RAM

• 320 Gb Hard Drive

• 2.66 Ghz processor

• DVD+/-RW with CD-RW Drive

Laptop

• LCD screen

• Portable

• 128/256 Mb RAM

• 20Gb HD

• 2.7 GHz processor

Palmtop

• Single user access

• LCD screen

• Touch sensitive screen using stylus

• Memory – 10Mb

Network Computer (not terminal)

• much like a desktop

• has own processor

Terminal

• has no processor

• dumb terminal

• no backing storage of its own

Distinguish between different parts of memory

Type

Registers

Function

Internal to the processor. Holds data while being processed. IR

Speed of Access

Fast access time

Cache Stands between the processor and main memory. Holds instruction of recently used programs.

Slower than registers but faster than main memory

Type

Main Memory

Function

RAM stores data and software currently in use.

Speed of Access

Slower than registers and cache. However, faster than backing storage.

Backing Storage

Stores data, software. Retains data when power switched off.

Slowest of all the types of memory.

Measuring Performance

There are many factor that affect computer performance.

• Clock Speed

• MIPS (Millions of instructions per second)

• FLOPS (Floating point operation per second)

• Benchmarks

Clock Speed

The speed at which a processor executes instructions. Every computer contains an internal clock that regulates the rate at which instructions are executed.

The faster the clock speed the more instructions can be processed.

Measured in MHz and GHz. The computers control line carries out the clock pulse.

1 GHz = 1 thousand million cycles per second

How Good a measurement?

Not all instructions are equal certain instructions are more complex than others.

For example,

A basic

MIPS (Millions of instructions per second)

A old measure of a computer's speed and power, MIPS measures roughly the number of machine instructions that a computer can execute in one second.

However, different instructions require more or less time than others, and there is no standard method for measuring MIPS.

Refers only to processor speed

How Good a Measurement?

Outdated method of measuring performance.

Processors can processes 1000 million instructions a second.

Different instructions require more or less time than others

FLOPS (Floating Point Operations per second)

This measures how many floating point operations a processor can carry out in a second.

The arithmetical calculating speed of a computer system.

How good a measurement?

Only deals with the processor.

Benchmarks

A test used to compare performance of hardware and/or software.

A benchmark is the result of running a computer program, or a set of programs, in order to assess performance.

A standard set of computer tasks designed to allow a computers performance to be measured.

How good a measure of performance is it?

Provide the user with actual evidence of system performance in carrying out complex operations at high speed. Reliable method.

Factors that affect system performance

Data Bus

Cache

Transfer Rate

RAM

VRAM

2nd Processor

Bus Width

Address Bus

32 bit address bus can address 2 memory locations.

4294967296 possible locations

4194304 Kb

4096 Mb

4Gb possible memory locations

A computer does not always have full amount of memory that is possible because RAM is costly and computers do not always have their capacity.

How good a measure of performance is it?

Increasing the width of the address bus will allow the system to address more memory.

Not improve the system but will allow larger tasks to be undertaken without having to rely on virtual memory.

NOTE-Virtual Memory

When all the RAM is being used (for example if there are many programs open at the same time) the computer will swap data to the hard drive and back to give the impression that there is slightly more memory.

Data Bus

This allows the movement of data from the processor to memory and vice versa.

Increasing the size of the data bus increases the amount of data which can be transferred between memory and the processor in a single cycle.

Data bus 32 bit will have a word length of 32 bits.

How good a measure of performance is it?

Increasing the width of the data bus will allow more data to be fetched in a single cycle.

Data Bus

MAIN MEMORY

32 bit

32 bit

32 bit

The above data bus has a bus width of 32 = 32 bit Word Length

How many bits the computer can process in 1 operation.

Unique address

Data Bus

Front Side Bus (FSB)

The primary pathway between the CPU and memory. The speed is derived from the number of parallel channels (16 bit, 32 bit, etc.) and clock speed.

Back Side Bus (BSB)

A dedicated channel between the CPU and a level 2 cache. It typically runs at the full speed of the CPU, whereas the front side bus generally runs slower

L1

L2

CPU DRAM

CU

ALU

Main Memory

Amount of Memory

Extra memory can be added to a machine if it is struggling to run some software or cannot load all the software.

Holds the programs currently in use:

• Operating System (Windows XP)

• Applications (Microsoft Word, Internet Explorer)

• Data (Data Files)

Amount of RAM

256 Mb RAM – 1 – 2 programs

512 Mb – Several programs (edit photos)

1 Gb – 2Gb – Intense gaming, complex video editing.

How good a measure of performance is it?

• Allow larger programs and more data to be held in RAM.

• More RAM means more programs can run smoothly and simultaneously (same time).

• Improves the speed of you computer.

• With more RAM the user can browse the internet, look at pictures, and listen to music effortlessly at the same time.

Cache Memory

Made up of SRAM which sits between the processor and Main memory.

Cache holds copies of data and instructions that are commonly used by the processor.

L1

L2

CPU DRAM

CU

ALU

Level 1

• Cache is built into the CPU• Internal cache • 2Kb – 64Kb

Level 2

• Built outside the CPU• External• 256 Kb – 2Mb

How good a measure of performance is it?

Improves computer performance by storing the most commonly used instructions and data in SRAM.

Because many applications often use the same instructions or data repetitively, a memory cache can improve performance by storing these instructions or data in the faster SRAM rather than DRAM.

Buffers and Spooling

These are used to compensate for the difference in speed between the fast processor and the slower peripheral.

Buffers

An area of memory (on the actual peripheral or the interface itself) used for the transfer of data between the computer and a peripheral. Helps compensate for differences in the transfer rate of data from one device to another.

For example, a fast acting part of the CPU exchanging data with a slow acting printer.

Allows data to be transferred from the computer which then allows the CPU to get on with other tasks.

DATA BUFFER

How good a measurement is it?

This frees up the much faster processor so it can get on with other tasks.

The buffer reduces the frequency with which the CPU is interrupted to deal with input.

When data is being transferred to the CPU from a relatively slow input device, like a keyboard, a buffer is used to store the data until a significant block of data is assembled for the CPU to deal with.

Spooling

A program that intercepts the data going to a device driver and writes it to the hard disk. The data is later printed or plotted when the required device is available

Most operating systems come with one or more spoolers, such as a print spooler for spooling documents.

.

DATA Hard Disk

How good a measurement is it?

Just like the buffer it frees up the fast Processor to do other tasks. Which in turn can improve the computers performance.

Data Transfer of peripherals

All peripherals operate at slower speeds than the processor.

This can slow down processing. This means that selecting a drive with a faster data transfer rate can improve the overall performance of your system.

Example: CD Drive

CD transfer rate Transfer rate in Kb per second

52x 7800

32x 4800