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Stephen Coates
16th March 2008, 18:54
I have finally started working on the task for my college course which involves CAD.

Firstly, as I mentioned in the 'CAD Software' topic, I have to research 3 CAD packages and specify which one I will use. The first one I have stared writing about is AutoCAD 2008, which is what we have on the computers in college. Then I am going to write about Cycas, both the Amiga version and the newer Linux/Windows version, and for the third one I will probably use something for the Macintosh, maybe ClarisCAD or something.

However, these CAD packages will need a computer system to be run on. I think we only have to do one system, but I thought I would write about a system for each of the above CAD packes. As you probably guessed, I can quite easily specify an Amiga for Cycas, and wouldn't have much trouble specifying a 68k/PPC Mac for the Mac package (I havn't decided which one to use yet).

But, AutoDesk say that AutoCAD 2008 requires a 2.2GHz Pentium 4 processor :unsure: and my lack of knowledge of PC stuff made currently and during the last few years makes it difficult for me to determine what kind of hardware to use.

So, I thought I might be able to utilise your knowledge of modern computers. Here are the requirements for AutoCAD 2008:

Intel Pentium 4 processor, 2.2 GHz Recommended
Operating Systems:
Microsoft Windows Vista
Windows XP Home and Professional (SP2)
Windows 2000 (SP4)
512 MB RAM
750 MB free disk space for installation
1024x768 VGA with True Colour
Microsoft Internet Explorer 6.0 (SP1 or higher)

I would be grateful if someone could suggest to me some hardware which would run AutoCAD nicely. I'm guessing that something better than a 2.2GHz P4 would be ideal. I could really do with some advice on graphics cards and memory as well. Ideally, the system would run Windows 2000 as I like it more than XP, but that is not essential. I do not want to go within a 100 foot radius of Vista. The drawings will not really require anything very powerful as they are quite simple. I don't think it would benefit from having multiple/dual core processors therefore it would be easier to stick with single ones. Doesn't have to very recent either, as long as it is better than the above requirements.

Many thanks
Steve

Buleste
16th March 2008, 20:15
To be honest if you want something to fill those specs then any generic pc from any store would work although you would have to make sure they don't put Vista on. If you want a cheap option you could try joining your local freecycle group and see if you can pick one up for nowt (that should apeal to the Yorkshireman in you) or try thier sister site where you can pick up stuff for next to nowt.

Zetr0
16th March 2008, 20:41
@Stephen Coates

Well from the specs its quite a simple build in all honesty, and a cheap one too

if you were building this from scratch including the lot here goes

A quick build 520.09/*300.53 without monitor/OS


XP4400 Dual Core 64bit
2GB DDR2 PC800
Radeon XT1950 Pro 256MB GDDR3 graphics
Sharkoon Rebel Chassis
550Watt Silent PSU 24pin
250GB SATA2 HDD
Asus MultiLayer Optical DVDRW
19" LCD Monitor with 5ms refresh and 300cd/m2
Keyboard
Mouse
Speakers


The components in greater detail

chassis 25.84
http://www.scan.co.uk/Products/ProductInfo.asp?WebProductID=527915

PSU 19,85
http://www.scan.co.uk/Products/ProductInfo.asp?WebProductID=132721

motherboard 36.54
http://www.scan.co.uk/Products/ProductInfo.asp?WebProductID=775027

processor 43.23 - XP4400+ x2
http://www.scan.co.uk/Products/ProductInfo.asp?WebProductID=632503

memory (RAM) 2GB DDR2 PC800 23.48
http://www.scan.co.uk/Products/ProductInfo.asp?WebProductID=527001

Graphics ATI Radeon X1950 Pro 256MB GDDR3 78.24
http://www.scan.co.uk/Products/ProductInfo.asp?WebProductID=673526

hard disk Maxtor 250GB SATA2 34.19
http://www.scan.co.uk/Products/ProductInfo.asp?WebProductID=510721

Optical Drive ASUS DVDRW Multi Layer 16.44
http://www.scan.co.uk/Products/ProductInfo.asp?WebProductID=787238

Keyboard / Mouse / Speakers 11.74
http://www.scan.co.uk/Products/ProductInfo.asp?WebProductID=215574

TFT Monitor 19" Asus 5ms 300cd/m2 132.27
http://www.scan.co.uk/Products/ProductInfo.asp?WebProductID=644855

WinXP Pro SP2 85.06
http://www.scan.co.uk/Products/ProductInfo.asp?WebProductID=487054

For the complete kit above 520.09 (+10 PnP)

Stephen Coates
16th March 2008, 22:27
To be honest if you want something to fill those specs then any generic pc from any store would work although you would have to make sure they don't put Vista on. If you want a cheap option you could try joining your local freecycle group and see if you can pick one up for nowt (that should apeal to the Yorkshireman in you) or try thier sister site where you can pick up stuff for next to nowt.

Note that I won't actually be buying such a system, but just need to research it and list the specifications etc. But the knowledge will of course remain with me should I ever want a new PC in the future. Regarding freecycle, I joined a while ago, but so far havn't got anything.

Zetr0: Cheers for the links. Definately a little bit confusing with the processor/graphics card. Is that quite a high end system by todays standards or is it quite low end? (Shows how up to date I am). I will look at those parts in more detail tommorow.

Zetr0
17th March 2008, 00:08
@SC

I would say its Mid to High end, I would personally consider it an entry level gaming system. this would be able to play all the latest games with 90% of the features enabled.

you could reduce this more by shopping around, note the 300 price tag without OS or Monitor, so if you wanted a Linux box and already had a decent monitor or KVM it would be very cheap for the specification, compared to off the shelf systems from like PC world or other main dealers like DEL.

If you were to Base a PC on the specifications that you have for the program, then its would be under 200, but it would be limmited as well as most of the parts would likely be second user, as the main PC buying market is pushing core duo and AMD's Phenom based products one could be hard pressed to find a single core P4 at 2.2ghz let alone a 462 motherboard of that specification out side of ebay.

Harrison
17th March 2008, 10:57
If you want to specify a workstation for running CAD, rather than actually looking to purchase one for real then any of the specs listed here are too low. And the reason for that is that those specs are a minimum. To do serious business related CAD work these days you need quite a high spec workstation with a specific workstation grade graphics card.

Steve, something you need to consider in regard to CAD is that for anyone using AutoCAD professionally any of the systems already listed, and the minimum specs for the application are nowhere near to what is actually required for real world use of the application.

Firstly you will never see anyone using a CAD package on a small monitor. Expect to see at least 21" monitors as a minimum, and these days you are more likely to see at least 26" or more likely 30 screens being used. Why? CAD requires high levels of detail for the accuracy needed when designing so the larger the screen and the higher the resolution the better.

You mentioned about not needing dual core, but 3D and CAD is the only area that all programs are actually optimised for multicore CPU use. The benefits from utilising multi core processing for such programs is big as there is a lot of processing going on once a schematic or 3D realisation of the finished product starts to increasing in complexity and a single core CPU will start to struggle when this happens.

Next for ram, the more you can get in the system the better as CAD and 3D will eat through ram very quickly. As mentioned above a lot of CAD drawings are eventually concluded with a 3D rendered visualisation of the completed design. The more ram you have, the faster the system will be able to process and move around the design as you work, and the faster the final rendered concept artwork will be completed.

For AutoCAD 2008 I would recommend the following minimum spec.

Intel Core 2
4GB Ram
nVidia Quadro FX 570 or ATi FireGL v3600 graphics card
74GB SCSI HD
24" LCD

Obviously you don't need a sound card for such a system. And the graphics cards I've listed are both entry level workstation cards from both of the main makers, although Matrox cards are also used for CAD and Video workstations often. Why pick workstation cards rather than normal mid to high end gaming cards? The main reason is that workstation card drivers are optimised specifically for a handful of applications. These normally including 3DSMAX, Maya and AutoCAD.

Also an Intel Core 2 CPU is probably not an option most workstation buyers will go for. They will instead normally go for an Intel Core 2 Quad Extreme at the lower end, up to quad core Xeon in more workstations these days, and quite often dual Xeon motherboards these days allowing for 2x quad core CPUs in the same system.

To give a good idea of a full system at the entry level of workstations used for CAD and 3D have a look at the Armari site found at http://www.armari.co.uk and look at the Magnetar QS system. Even though his is an entry level system it might still sound expensive at 1,599 but remember that these systems are using workstation grade components, not home user grade parts.

Most CAD workstations will cost more like 10,000 and for most professional CAD companies that isn't seen as expensive.

You might think I'm being silly with these specs, but I am not. These are realistic specs for systems currently being used in companies to run AutoCAD. It requires a lot of processing power.

Yes, any entry level PC purchased from somewhere like PC World would today be able to run AutoCAD, but it wouldn't be nice as a workstation designed to professionally use AutoCAD with.

Obviously if you just want to specific a system that can run AutoCAD to learn it for say university course work then a dual core Intel Core Duo CPU, 2GB Ram, 300GB HD, any mid to high level gaming spec graphics card that supports OpenGL and a large monitor of 24"+ will work fine.

Buleste
17th March 2008, 11:10
@ Harrison
Why SCSI HDD? I would have thought a SATA2 drive would be just as good and cheaper to get a larger drive plus no need for a SCSI card.

Harrison
17th March 2008, 11:11
Forgot to mention something else. Nearly all AutoCAD users these days run the 63bit versions of their OS of choice. This allows much faster processing of the specific operations CAD software uses, and allows them to address more than 4GB (which is the limit of 32 bit OSs). It is not unheard of for many CAD workstations to have at least 8GB of ram, and some I've seen recently have 64GB. Very nice!

As for the specific OS, you can actually get AutoCAD for Linux and many run SUSE, Red Hat or another business supported Linux Distro for CAD use. Others run 64-bit Windows XP. I've not yet seem anyone running 64-bit Vista because as far as the business world goes it is too new and the workstation grade graphics card drivers are not mature enough yet.

No one runs Windows 2000 any longer though and a lot of software won't even run on it. 3DSMAX and all Adobe software for example will not install or run under Windows 2000. Not sure if AutoCAD has completely dropped support for 2000 yet, but it will very soon if it hasn't already.

Harrison
17th March 2008, 11:16
Business and design workstations all still use Ultra SCSI. It is a much faster continuous throughput compared to SATA which is normally specified in burst rate which is not a continuous speed.

Take Ultra-640 SCSI for example. This has a 640MB/s throughput and can support 16 devices on the chain. In comparison SATA2 has a real world maximum data rate of 300MB/s.

Ultra SCSI drives are still mostly used in video and 3D workstations too, rather than the cheaper SATA drives. However you could get away with using SATA2 drives for a lower cost system.

Buleste
17th March 2008, 11:21
I'm thinking as it's a college project i would say that it would be going in for the cheaper option (Yes i know steve this is all hypothetical). Thats a point SC, even though this is a hypothertical question what max budget would you give and what lifespan would the PC need?

Harrison
17th March 2008, 11:46
Because it is hypothetical I decided to list the realistic specs that a CAD workstation would be built around these days. When talking about theoretical specs for a system in college work then you should really be looking at the current real world specs, rather than something that can just about run the application that in the real world would be impractical.

For budget the realistic minimum has to be 2000, although for a home based CAD designer or university student you could build a PC for around 1000 including monitor that would run AutoCAD at a reasonable speed.

Buleste
17th March 2008, 11:57
Right i'll have a look on Overclockers to see what i can find.

Stephen Coates
17th March 2008, 12:51
Not really sure about lifespan or price. We are just researching possible options and specifying which one would be best.

I'm not sure if we actually have to produce a drawing, but if we did have to do one in AutoCAD it would most likely be done on the computers in the library which i think are dual core Intel systems, with 1280x768 monitors (probably either 17" or 19"). For this project, I would think that these systems would be quite suitable, but this is research into CAD packages and computers which would be suitable for this project and an expensive workstation would be suitable as well, as I'm sure a fast amiga running Cycas would be :boing: (We are doing a bicycle suspension which isn't too complicated).

Thanks for the information harrison.
*thinks about copying harrison's post into assignment to save work :JRflag:;)*

I know AutoCAD has a 64bit version so I can't see any reason why that can't be used. This obviously makes Windows 2000 useless although I can't really moan about a properly set up XP Pro. AutoCAD does still support Windows 2000 as I mentioned in my first post harrison :p.

The teacher did say to look into workstations and operating systems other than windows, so i will look into workstations and include them. I might say something about a desktop computer and then compare it to a workstation.

Buleste
17th March 2008, 14:40
Try here. (http://www.solidapps.co.uk/Hardware.shtml) It seems to have some good info as to what is good for a CAD workstation and some sample workstations.
Or here. (http://www.excitech.co.uk/hardware/hp_pcs.asp)

Harrison
17th March 2008, 16:02
AutoCAD does still support Windows 2000 as I mentioned in my first post harrison :p.

Yes it is still compatible with Win2000, but Windows 2000 is now no longer supported by M$ so is an obsolete OS and no business will buy into it these days. Only companies with an existing set of licenses will still considering continuing to upgrade AutoCAD and keep 2000 as the underlying OS. All new systems will either have XP Pro, XP Pro x64 Edition, or Windows Server 2003. As I mentioned before, you won't find anyone using it with Vista yet, but many may look at the option of using Windows Server 2008 once it gets released.

Why use a server OS? There are loads of advantages over a standard desktop OS. Much more optimised for stability and the ability to customise the services running on it to streamline the OS to the exact needs of the user. Support for as many physical CPUs as you like. XP still has a limitation of two physical CPUs, although not the number cores each contains.

Plus Windows Server 2003 is the more logical upgrade root from 2000 than XP is. And if you like 2000 then you will really like Windows Server 2003, and the forthcoming 2008 as they are based more on the idea of 2000 as a business OS without all the consumer crap bolted on to slow the OS down. Which is another reason for companies to look into using 2003 over XP for workstations as it doesn't contain any of the consumer stuff they don't need.

Stephen Coates
3rd April 2008, 13:45
Harrison, what do you mean about AutoCAD for Linux?

As far as I'm aware, there is no longer a linux version and the only version now is for Windows.

Buleste
3rd April 2008, 14:15
Don't know about AutoCad but try here (http://www.tech-edv.co.at/lunix/CADlinks.html) for a list of linux based CAD applications.

Harrison
3rd April 2008, 15:47
I just had a quick look on the Autodesk site and they are indeed not mentioning Linux for the latest releases of the many derivatives of AutoCAD (quite mad how many they now have available). However I do know that AutoCAD 2008 does support Linux and has a Linux installer on the same install disc as the PC version. I would be quite surprised if they had dropped it from the new AutoCAD 2009 but I didn't see any mention in the quick click about I did on their site.

Stephen Coates
3rd April 2008, 16:00
Well, I have not heard of any Linux version of AutoCAD 2008. I read that there used to be a Linux version a few years ago.

Stephen Coates
15th April 2008, 10:50
Business and design workstations all still use Ultra SCSI. It is a much faster continuous throughput compared to SATA which is normally specified in burst rate which is not a continuous speed.

Take Ultra-640 SCSI for example. This has a 640MB/s throughput and can support 16 devices on the chain. In comparison SATA2 has a real world maximum data rate of 300MB/s.

Ultra SCSI drives are still mostly used in video and 3D workstations too, rather than the cheaper SATA drives. However you could get away with using SATA2 drives for a lower cost system.

Harrison, do you know much about Ultra-640? I had a look on the internet but couldn't find much which seemed to make sense.

I know that it is 640MB/s, but I was wondering, does this speed get affected depending on how many devices you have on the chain?

Harrison
15th April 2008, 16:06
SCSI Ultra 640 was first introduced in 2003 and has a maximum sustained throughput of 640MB/s (hence the name) which is over twice that of SATA2's 300MB/s maximum burst rate. It uses either standard 68 pin high density connectors, or the slightly newer 80 pin connectors, and supports up to 16 devices on the chain, with each needing its own ID (or LUN - Logical Unit Number), and the last device in the chain needs to be terminated so the signal is reflected back down the cable correctly.

So basically it works in the same way as all SCSI versions and the cables are the same as have been used since Ultra Wide SCSI and then Ulta2 Wide SCSI were first introduced back in the mid 90's.

As for your question about the speed of the interface depending on the number of devices. SCSI is shared bandwidth, much like IDE, so the more devices on the chain, the less bandwidth each device will have. In contrast SATA is device independent so all devices get the full bandwidth (in the case of SATA2 all devices would have full access to 300MB/s each). Therefore you can instantly see the initial advantage of SATA over SCSI once you start to have more physical devices attached to a system.

But you do also need to consider other things and this shows reasons why SCSI is often still chosen over SATA. SATA drives still mostly tend to spin at 7200RPM, whereas SCSI drivers are mostly 10K or 15K, so their seek times are much faster. The other is the physical actual data rate of the drive. Most SATA drives still only have a data rate around 50-60MB/s maximum, so even though they are on a 300MB/s SATA connection they wont be using it all. In contrast SCSI drivers are commonly around the 89MB/s range, with some recent ones supporting 150MB/s! Therefore although SCSI shares bandwidth, if you had 4 drives connected to one interface you would still be able to maintain the full 89MB/s x4 bandwidth (356MB/s total) and even the full bandwidth of 4 150MB/s drives, and when you compare this to 4 devices connected via SATA, each on their own independent 300MB/s bandwith, the SCSI will still be faster as each SATA device will probably only be managing around 60MB/s max, for a total of 240MB/s across all 4 drives combined. So you can see the advantages of SCSI over SATA still.

Obviously if you were to start having more tha 4 devices on a SCSI chain it would start to eat into the total shared bandwidth, especially if you were using HDs with 150MB/s data rate. And then SATA might start to be a better solution. Faster SATA drives are starting to appear with faster spin rates and faster data rates closer to those of SCSI drives so SCSI is starting to look less appealing.

Also with SATA having independent bandwidth per channel, you can utilise something called a port splitter. This allows you to connect 4 physical SATA devices to a single SATA channel on the controller and utilise the 300MB/s bandwidth per channel, shared between 4 devices which is more than enough bandwidth to access 4 average SATA HDs. You could therefore add 4 port splitters to a 4 channel SATA card and have 16 physical SATA HDs connected, all accessible at full bandwidth. You couldn't do this with SCSI.

One thing worth noting is the Ultra 640 is probably going to be the last of the original Parallel SCSI type. Serial SCSI and iSCSI are now taking over, as well as most manufacturers now including SATA instead of SCSI on their motherboards. Serial SCSI has the big advantage of supporting hot swapping and faster data rates. Whereas iSCSI is SCSI over TCP/IP which is idea for use with Fibre Optic cabling.

Stephen Coates
15th April 2008, 17:43
*brushes up on 'write it out in your own words' skills* ;)

That was interesting to know. Got any recomendations of SCSI hard disks and controllers?

Would this 640MB/s maximum be affected if it was on a PCI card? I'm not sure how fast PCI and it's newer whatsits are.

Also, I got a little confused when reading about this on other sites. Does this increased speed affect the maximum cable length?

Harrison
15th April 2008, 17:48
Cable lengths are about the same. There is a bottleneck with a standard PCI bus because it can only support 133MB/s shared across the whole PCI bus, so a SCSI card connected on a standard PCI bus would need to share bandwidth with any other PCI cards such as network and sound.

In more professional systems there are alternative faster system bus types that SCSI is connected to which doesn't have such limitations. Even more so if the SCSI controller is integrated into the motherboard.

Stephen Coates
15th April 2008, 20:27
What could be used instead of PCI?

How fast is PCI Express then? Would that be suitable for using an Ultra 320 controller on?

Harrison
15th April 2008, 21:54
Servers until recently have used PCI-X slots. This type of slot was developed purely for servers in the 90's and uses a 64bit bus running at either 66MHz or 133MHz which gives a maximum bandwidth of 527MB/s and 1064 MB/s respectively. So much faster than standard PCI slots in a home computer. Systems with these are a lot more expensive and is part of the reason that pro workstations and server do cost much more than a standard PC.

PCI-X slots use a parallel interface that is directly compatible with standard 5V PCI devices so you can still use normal PCI cards in them as well as faster PCI-X specific cards. And likewise most PCI-X cards will work in a slower 32bit PCI slot.

The 133MHz PCI-X slot is the most common found in servers giving 1064MB/s.

But there are two faster standards developed in 2003 under the updated PCI-X 2.0 standard. This adds 266MHz and 533MHz variants to the standards, giving roughly 2.15GB/s and 4.3GB/s respectively. Now this is fast! Although these types of slot and supporting cards are very rare and extremely expensive.

And PCI-X slots are slowly being replaced with PCI-Express (PCI-e) slots and cards. PCI-e slots are very different. PCI-X slots are based on normal PCI slots and the PCI-X cards are backwardly compatible with standard PCI slots and PCI-X slots use a parallel interface.

In contrast PCI-e is a serial interface and is not compatible with any other interface type so you couldn't use a PCI card in a PCI-e slot. And PCI-e is much faster. The slowest x1 offers 250 MB/s in both directions, and currently the fastest slot is now up to x32 offering 8 GB/s bandwidth which is twice that of the rarest fastest PCI-X slots available.

PCI-e also has many other advantages over PCI and PCI-X. Due to the older PCI standards being parallel interfaces the trace routing has to be much more complex and able to deliver all signals at the same time across the interface. It also suffers from a lot of noise from adjacent slots which can cause interference. In contrast PCI-e's serial interface is much simpler with much less traces needed and it is also full duplex bidirectional rather then the half duplex bidirectional of PCI-X and PCI.

Stephen Coates
17th April 2008, 20:29
Ahhhh. PCI-X. When I said PCI-X I actually meant PCI Extreme.

I got the X and E mixed up. Why did they have to make it so comfusion?

Harrison
17th April 2008, 22:15
That has always been the problem in the computer world. Different companies working on slightly different versions with the same end goals in mind and all with similar names. At least now we seem to finally be converging into a single standard for each thing. PCI-E slots for all expansion cards, SATA for drives and USB2 for external devices. So much easier, and I still think it is quite amusing that we have gone full circle from serial interfaces to parallel and now back to serial.

Stephen Coates
17th April 2008, 23:19
I'm still getting the Extreme and the Express mixed up.

So, just to summarise,

PCI-X is PCI-Extreme and is the one which is compatible with PCI
PCI-E is PCI-Express and is the other one.

Assuming that I havn't got them the wrong way round again, I think that the X should stand for Express and E should stand for Extreme.

Harrison
18th April 2008, 00:40
Yes you have them round the right way now. :)

And I agree, still confusing for most people.

Technically PCI-X is the extreme version of PCI because it has much more bandwidth due to the cards being much longer with a lot more connections in the slot/card design to add the extra needed parallel traces.

And I personally think they should have named PCI-E something completely different without using the PCI name at all because unlike the previous slot types it isn't compatible with them and therefore isn't in the same family. It's a completely new serial slot design and using PCI in the name just adds more confusion. Although as PCI stands for Peripheral Component Interconnect you can see the logic for keeping it too.

Stephen Coates
18th April 2008, 08:09
That makes sense. If PCI doesn't stand for something specific then it would make sense to keep using it if PCI-E is also a 'Peripheral Component Interconnect'.

Kindof like PC. When people refer to IBM compatible PCs as just a PC. Well, it is a personal computer, but so is a Macintosh.

I decided to go for dual quad core Xeon 5300s at 3GHz. No idea how good that would be, but I assume it would be more than fast enough. I also opted for a nVidia Quadro FX 1700. Again I don't know how good it is but it would probably be suitable. Will certainly be expensive though. I think the graphics card is priced at around 200 and dual xeon motherboards also seem to be around that as far as I can tell.

For hard drives I went for Seagate Cheetah 15k.5 ones. They use Ultra320, have a maximum speed of about 120MB/s spin at 15000RPM. I went for the 146GB option, but there were sized like 300GB and 74GB.

Why is it that SCSI HDs always tend to come in odd capacities, like 74GB and 36GB, when IDE ones just tend to be 40GB, 80GB etc?

Buleste
18th April 2008, 09:51
IDE's lie. For instance a 20GB HDD is actually 18.8GB. personally i think it's because IDE is used by the great unwashed so they round them up/down where appropriate but as SCSI is generally used by more computer literate people who want to know the true size. Thats my opinion anyway.

Stephen Coates
18th April 2008, 10:18
That's what someone else told me yesterday. Couldn't the formatting affect the amount of space though, like with a DD disk being 1MB, when formatted it is only 880k? I'm not sure how the formatted capacity of SCSI HDs differs from that of IDE/SATA HDs.

Buleste
18th April 2008, 10:53
I don't think it does. IMO It's just that the figure given on SCSI is post formatting and the figure for IDE is Pre formatting.

Harrison
18th April 2008, 12:30
It's actually how data sizes are interpreted. We all know that 1MB = 1024KB and 1GB = 1024MB. But HD manufacturers instead decide to state HD sizes based on 1MB = 1000KB and 1GB = 1000MB.

This makes the HDs look slightly bigger, but obviously when you format them the computer is using the proper data sizes of 1GB = 1024MB to display capacity, so when you compare the two it always looks like you have lost some space on the drive once it has been formatted.

So if you convert it. A 20GB HD is actually really 19.53GB unformatted.

Plus you will always lose some HD space from the true total as well once formatted because the structure has to keep some of the space back for housekeeping and indexing needs.


Why is it that SCSI HDs always tend to come in odd capacities, like 74GB and 36GB, when IDE ones just tend to be 40GB, 80GB etc?

This is due to the faster spin rates of most SCSI drives compared to IDE and SATA. Due to 15,000RPG drives spinning at least twice that of standard IDE/SATA 7,200RPG drives the data rate and seek times are increased, but capacity suffers.

If you also look at the fastest IDE drives they also come in these lower odd capacities too. Have a look at the Western Digital Raptor range to see this.