PC Construction and Maintenance

Week 11

Advanced Topics

SCSI,RAID,TV,DVD

Alternative Operating Systems

Appendix to week 10 – re-installing windows

SCSI

• Small Computer Systems Interface

• This is a misnomer, SCSI is now generally used on high-end servers

• Supports Hard Disks, CD-ROM Drives, Scanners and Tape Drives

• SCSI system provides a separate bus and associated controller chip

SCSI – physical form

• Usually, SCSI controllers are purchased in the form of a PCI peripheral card

• Some expensive motherboards have on-board SCSI controller chip

• SCSI supports internal and external devices• Multi-connector ribbon cables are used to

interconnect internal devices. SCSI devices are ‘daisy chained’

• Hint- if your case has a TURBO LED, you can plug it into the SCSI card

SCSI revisions

• SCSI-1 now obsolete• Most common SCSI devices are SCSI-2 (Commonly

known just as SCSI)• High end – Ultra high speed devices are SCSI-3 • SCSI devices can be either 8-bit, or 16 bit• 8-bit devices use 50 pin cabling, 16-bit devices use 68

pin cabling• 8 & 16 bit devices can share the same bus• Mixing SCSI-2 and SCSI-3 devices will incur a speed

penalty for fast devices

SCSI Implementations

Bus Width

Number of pins on cable

Standard Fast Ultra Ultra-2

8-bit 50 5Mb/s 10Mb/s 20Mb/s 40Mb/s

16-bit 68 10Mb/s 20Mb/s 40Mb/s 80Mb/s

When to use SCSI

• Servers. The benefits of SCSI are overwhelming in multitasking environments under constant heavy I/O load

• Very high-spec Audio/Video/Multimedia processing.

• Critical data. SCSI can provide support for data redundancy

SCSI vs IDE

• IDE is cheaper and easier to install and configure• SCSI supports command queuing – this is

beneficial for multiple devices sharing the same bus

• SCSI supports up to 8 devices on a bus (32 for SCSI-3) IDE, only 2 per controller

• Fast IDE devices ‘clobber’ the CPU, SCSI offloads the processing to the RISC-based controller chip

Constraints on connectingSCSI devices

• The problem of termination often causes headaches. Termination is needed to prevent reflected signals

• The devices physically situated at each end of the SCSI daisy chain must be terminated

• Termination circuitry is provided on most internal devices, and set via a jumper

• For external devices, a terminator must be plugged in• No more than four inches of extra cable can overhang

the end of a SCSI chain• All devices on the bus must have a unique SCSI ID

SCSI ID settings

• SCSI ID ranges from 0-7• Even the controller card is assigned an ID, which

is typically 7• To set the ID of a Hard Drive, you need to

configure jumper settings on the drive• There is usually a row of 3 consecutive jumpers

labelled 1,2,4 (or often 0,1,2 – meaning 20,21,22)• The sum of these jumper values determines the

SCSI ID of the device

RAID• Redundant Array of Inexpensive Disks• Can purchase a SCSI-RAID card as a PCI peripheral card• RAID typically used in a SCSI environment, as many

disks usually employed• Can get IDE RAID controllers now though – very cheap• RAID is used for the following two reasons. 1-

performance, 2-protection against data loss• Different “RAID levels” are used for different purposes• The RAID level is usually configured in the RAID-BIOS

menu

RAID 0 - Striping

• RAID level 0 is used for high performance• RAID 0 takes advantage of parallelism

across multiple disk drives• RAID 0 offers no extra protection against

loss of data• If one disk in the array fails, then data on all

disks is effectively lost• RAID 0 requires a minimum of 2 disks

RAID 1 - Mirroring

• RAID level 1 is used to offer protection against loss of data

• Identical data is written simultaneously to two disks

• RAID level 1 is quite expensive, as only get effective use of one disk for the price of 2

• RAID level one is only used in critical systems• Normally, RAID one requires only a single

controller, but two controllers can be used for a performance increase. This is known as duplexing

RAID 0+1 – Striping & Mirroring

• RAID 0+1 uses four disks to do both mirroring and striping at the same time

• This method offers both high performance, and protection against loss of data

• This method also suffers from the high costs of the RAID 1 system

RAID 5 - Parity

• RAID 5 consists of a number of disks, and one extra disk effectively for parity checking

• This method allows for protection against data loss, without the cost overhead of the RAID 1 configuration

• If any one disk in the RAID array fails, then the system can still retrieve the data from the parity information

• RAID 5 requires a minimum of 3 drives• RAID 5 is the most common RAID system in use

Other RAID levels

• RAID levels 2,3,4,6,7 are rarely commercially implemented

• They are just other combinations of mirroring/striping/parity and similar mechanisms

• We just need to know about levels 0,1,0&1 and 5

TV cards

• Most TV cards are of the PCI type, although some are external USB, useful for laptops

• Some TV/Graphics cards are sold as an integrated card usually AGP

• TV cards allow RF-input, composite video for connection to an antenna and other AV equipment

• Some TV cards allow the reception of digital TV

Advantages of TV cardsover “ordinary TV”

• Teletext mode can view a large number of pages simultaneously, can save pages to disk, either as plain-text or bitmap

• Can often freeze-frame TV, and save an image• Can save TV programmes onto hard disk, and

watch later• Refresh rates on monitors are higher than TV,

picture can appear less flickery • TV cards can also be used to convert video tapes

etc to digital format

DVD drives

• DVD drives use optical discs that are the same dimensions as conventional CD disks

• All DVD drives can read CD-disks

• There are two ways in which a computer with a DVD drive can show DVD movies, Hardware and Software

DVD drives

• DVD drives use optical discs that are the same dimensions as conventional CD disks

• All DVD drives can read CD-disks• There are two ways in which a computer

with a DVD drive can show DVD movies, Hardware and Software

• All new computers should be fitted with a DVD drive

DVD capacity

Disc

Type

CD-ROM DVD-Single-sided

Single-layer

DVD

Single-sided

Dual-layer

DVD

Double-Sided

Dual-Layer

Capacity 0.7Mb 4.5Gb 8.5Gb 17Gb

DVD: Hardware or Software

• DVD movie disks use digital compression known as Mpeg-2, and they are encrypted

• To display a DVD movie, A PC must have enough power to decrypt, and decode the movie on the fly.

• Computers of around 600MHz or faster are fast enough to display DVD movies using the main CPU, and a software program such as WinDVD or Power DVD

• Computers slower than this must be fitted with a DVD-Decoder card to display movies

DVD drives and regionalsettings

• DVD movies are region encoded e.g. region1=north America, region 2=Europe&Japan etc

• You can remove the region encoding by changing the firmware in your DVD drive

• If you do this, then you will be able to watch movies from any continent

• The firmware to do this is widely available on the web

Alternative Operating Systems

• Linux is becoming more popular• It is a pure 32-bit OS, and is just as much a ‘UNIX’

operating system as any other UNIX systems• UNIX is an operating system that pre-dates windows• Windows systems (most notably Windows 2000)

borrow a lot of underlying ideas from the UNIX world• Linux is free,or at least very cheap• Many specialist applications exist for linux

When to use Linux• Web servers, Mail Servers and other types of high-

capacity, high-volume servers often use Linux• Linux is used a lot it educational/academic environments.

It is a great platform for learning about computers• If you need to do serious number crunching, or parallel

processing across machines• To use any of the thousands of Linux apps that are

available, typically scientific applications• To learn about a system other that windows, from the point

of veiw of administration, or application development• For large organisations, to save money

Linux Distributions

• The Operating System is Supplied on several CDs, this is known as a “distribution”

• Two of the most popular distributions are RedHat and SUSE Linux

• RedHat Linux is American, SUSE Linux is German (and arguably better at the present time)

• For RedHat, often only a single CD is needed for the installation

Linux installation prerequesites

• It is recommended to have a spare hard drive dedicated to Linux, although it can share a disk with another operating system

• To start the install process we need either to boot off a distribution CD, or make a Linux boot floppy

• To make a Linux boot floppy, we use a DOS utility called rawrite .This is supplied with most distributions

• After inserting a blank formatted floppy, we use rawrite to write a file, boot.img , from the CD onto the floppy, sector by sector

• This image file contains the bootstrap program for the Linux installation

How to install Linux (RedHat)

• After booting from the install disk (floppy or CD), you can press <enter> to proceed with a normal install

• Sometimes you can activate text-only install mode if you are not sure that the graphics chipset on the computer is supported

• You should then select custom install to give yourself full control over the installation process

Disk partitioning under Linux

• We use the Linux version of fdisk to partition a disk for use with Linux

• This version of fdisk is very powerful, and supports a multitude of file-systems

• Linux systems need at least two partitions • One partition is used for files, and one is called the

swap partition for virtual memory• Make the swap partition at least twice the size of the

physical RAM in the computer• Many large Linux server typically use several partitions

Linux Desktop Environment• Linux is a very modular system, you do not need to run the GUI• The GUI itself is a layered system, comprising of the X-

windows system at the lowest level• X-windows is a client server system. You can run a graphical

application on the CPU of machine A, whilst physically sitting at machine B

• The desktop environment sits on-top of the X-windows system• Unlike Windows, there are many different desktop

environments that can be used• The two most popular are GNOME and KDE, you can install

both from the CD and compare them

Appendix A – Re-installing Windows

• There are two methods –

• 1. Overlay a new windows over the old copy

• 2. A fresh install

• Note: doing a fresh install does not imply removing the old copy off windows from the hard drive

Install tips

• It is always recommended to install windows from real DOS mode, often you have to anyway

• To speed the install up, and for great future convenience, it is recommended that you copy the CAB files from the windows installation CD onto the hard drive, before starting the install

• Do that under windows if it already installed, else use the XCOPY command under pure DOS mode

• The CAB contains every file needed by windows in a compressed cabinet format (not unlike zip files)

CAB files on the HD

• The CAB files are found on the windows CD under a folder called “win95” or “win98”

• After they have been copied to C:\win95 or similar, run setup from C:\, rather than the CD

• The install may be to 2-3 times quicker than running off the CD directly

• In the future, you’ll never have to dig the CD out again to add/remove components or change settings

Overlay the install

• Boot off a floppy, or via the hard drive into command prompt only (F8-key)

• Run setup and let the installer overwrite the existing files in C:\windows

• Reboot, and you may find that some previous problems on the computer have gone away

• You should not have to re-install any apps after doing this. All of your settings should be preserved

Fresh Install• Run regedit, and export the entire registry

file to C:\entire.reg

• Reboot to DOS via either floppy, or HDD with F8 option

Execute the following commands

C:

CD \WINDOWS

REN WIN.COM WIN.OLD

CD \

REN WINDOWS WINDOWS.OLD

Fresh Install cont.

• Run setup, and a fresh install will be performed• After rebooting, you may need to re-install most

of your previous applications (always the main Microsoft apps). Some apps will still work fine however.

• If you have lost some of the install disks, for some programs which no longer work, then you may be able to get them working again

Recovering old Applications

• Run the App, and see what error message you get, often it will be of the form “Cannot load somefile.dll” – It can’t find a shared file

• You will find the file in question either in C:\WINDOWS.OLD or C:\WINDOWS.OLD\SYSTEM

• Simply copy the file to C:\WINDOWS or C:\WINDOWS\SYSTEM accordingly

Recovering old apps cont..

• If the app still doesn’t work after restoring the shared files, then its registry configuration settings may be missing

• Load the file you created earlier C:\entire.reg into a text editor (one that is better than notepad)

• Do a search on the name of the program you are trying to fix, (or on the name of the software developer)

• You should find a block of text pertaining to the program in question

Registry hacks

• You can use the text editor to copy and paste the relevant section of the registry into a new text file, along with the very first line of the file (known as the header)

• Save the new “fragment” of the registry under a different file

• Load regedit, and import the new registry file• Once you have done this a couple of times, it seems

easy• Hopefully, you can finally run the old app without

problems