AbsoluteZero

32-bit/64-bit Pci/pci-x Confusion

Recommended Posts

Im building a system for my brother, and he wants a SCSI drive in his sytem. I got him an nforce2 ultra motherboard and not knowing, there are 2 diffeant kinds of PCI slots, I was about to order an ultra320 scsi controller card for the 15k RPM drive. my question is, Would it be better to buy a 64-bit controller card and run the 15k from the 32-bit PCI slot, or should I look for a 32-bit controller card and run a 10k RPM drive off of it? What would offer the best performance.

Adaptec makes a Ultra160 controller card for a 32-bit PCI bus but I cant find a 15K RPM drive to go with it. Only 10K. On the other hand, they make 64-bit PCI Ultra160 controller card that DOES fit most 15K dives. Would I lose the extra harddrive speed by running it through a 32-bit PCI? Or would it be faster then a ultra160 32-bit card with a 10K RPM drive.

P.S - I would assume Ultra320 would be totally useless in a 32-bit PCI slot.

Share this post


Link to post
Share on other sites

No, it wouldnt be totally useless in a 32 bit slot. It will still work...

In order to get 64bit PCI bus of any description, you generally have to jump to a server class motherboard... with such chipsets as Intel 7505, 7501, serverworks, or AMD 751 (? dual Athlon MP) ... I dont think the extra expense is worth it, (unless your building a server) ... In reality a 64 bit controller card will work in a 32 bit slot, if you still chose to go SCSI, you can use pretty much whatever controller you like...(with whatever drives you like)

However there will be a performace cap, that perhaps may mean that it would be wiser to go with EIDE or SATA drives, (financially)

Share this post


Link to post
Share on other sites

The server boards are alittle extreme. But I would still like to have SCSI in my system, no matter the price.

Would it be faster to use a ULTRA360 64-bit controller card in a 32-bit PCI with a ULTRA360 15000RPM drive

or

An ULTRA160 64-bit controller card in a 32-bit PCI with a ULTRA160 15000RPM drive

or

An Ultra160 32bit controller card in a 32-bit PCI with an Ultra160 10000RPM

so pretty much, will the not taking full advantage of the 64-bit PCI controller card slow it down to speed of a 32-bit PCI controller card? Does an Ultra160 15000RPM drive take FULL advantage of the 64-bit PCI interface?

Share this post


Link to post
Share on other sites

Your 64-bit card should work in a 32-bit slot.

Using a 32-bit card in a 32-bit slot is not any slower (or faster) than a 64-bit card in a 32-bit slot.

You'll be fine with a U160 controller and the 15k rpm drive.

I have a Adaptec 39160 with a couple of Cheetah X15s, and the 64-bit SCSI card is plugged into a 32-bit slot (standard PCI).

Basically, whatever is less expensive....as long as you're getting a name brand SCSI card. U160 or U320 will overwhelm the PCI bus (burst speed).

If you want to see 160MB/sec or 320MB/sec you'll need to get a PCI-X motherboard.

DogEared.

8^)

PS You're drive only cares if the SCSI bus is U160, or U320, etc. The Drive doesn't know if you're connected to a 32-bit or 64-bit card.

Share this post


Link to post
Share on other sites

I should also have said:

U320 drives will work on U160 busses (cards) and U160 drives work on U320 busses.

So you can mix and match. But the bus speed will adjust to the lowest speed needed for any device.

If you'll be running a u160 drive, don't bother with a U320 card...unless you're getting a deal. :)

DogEared

8^)

Share this post


Link to post
Share on other sites

OK, its making sence, but lets clarify.

The 15k made for Ultra160 64-bit PCI will still have the extremly fast seek time (loading games/windows) in an Ultra160 32-bit PCI, but transfer wont be as fast as It could be. right?

So, would it be even FASTER to get an ULTRA320 SCSI and run it though a 32-bit PCI bus? I know It wont get transfer speeds, but will it load apps. even faster then the 15k U160?

you guys rock.

Share this post


Link to post
Share on other sites
OK, its making sence, but lets clarify.

The 15k made for Ultra160 64-bit PCI will still have the extremly fast seek time (loading games/windows) in an Ultra160 32-bit PCI, but transfer wont be as fast as It could be. right?

So, would it be even FASTER to get an ULTRA320 SCSI and run it though a 32-bit PCI bus? I know It wont get transfer speeds, but will it load apps. even faster then the 15k U160?

you guys rock.

1) Right. Seek times down. but transfere rates wouldnt be as impressive... in the end I think they'd (nearly) ballance out, and you wouldnt notice the difference...

2) U320 is faster than U160. However on a desktop capped by the PCI bandwidth, I dont think you'd make effective use of this extra speed... It maybe faster, but considering the price difference, I dont think it would be THAT much faster...

Share this post


Link to post
Share on other sites

You shouldn't see a difference.

PCI Bus == 133MB/sec

110-120MB/sec of disk bandwidth is as much as you should expect.

(100MB/sec I think is more common)

Since, U160 (@160MB/sec) and U320 (@320MB/sec) are both faster than the PCI bus you won't see a difference. The PCI bus is your bottleneck not the SCSI card or the drive.

You'll still get the low access times, and the higher sustained transfer speeds, but you won't see a benefit to U320.

Get the 15k drive and U160 card.

DogEared

Share this post


Link to post
Share on other sites

Keep in mind that even the fastest 15k SCSI drive can only sustain maybe 80MB/sec from the physical disk. Unless you're getting multiple drives and planning to use them concurrently, you won't even be able to max out the U160 interface. The only time it'd be of help is transferring from the HD buffer, which in the best case would last you all of 50ms at 160MB/sec before it has to go back to the physical disk.

Share this post


Link to post
Share on other sites

To add another voice of sanity:

The fastest hard drive on the market today in terms of raw transfer speed, the Fujitsu MAS3735 (as listed on the SR Performance Database,) will manage a maximum of just short of 80MB/s of transfer, from platter to buffer.

80MB/s is slower than PCI 32-bit, 33Mhz, and slower than Ultra-160 SCSI.

The drive will absolutely, positively, be the limiting factor with current hard drives.

It doesn't matter wether your SCSI card is Ultra-160 or Ultra-320 (for that matter, one single drive will even come short of totally maxing Ultra2's 80MB/s.) It doesn't matter if it's PCI 32-bit, 33 MHz, or PCI-X 64-bit, 133MHz.

The biggest factor isn't even raw platter-to-buffer speed. That really only matters when you're dealing with sequential transfers. Even AV capture at full HDTV resolution doesn't need 80MB/s. The only time it would really matter is making a copy of your hard drive.

The biggest factor isn't seek time, either. That only really matters on truly random seeks.

One of the biggest points SR stresses is that raw numbers don't really amount to squat. Look at the Performance Database, and compare drives in the categories that this computer will actually be used.

If it will be primarily a gaming machine, the Maxtor Atlas 15k and Fujitsu MAS are only slightly ahead of the significantly cheaper to implement Raptor 74. If one tenth of a second really matters when loading a level in Doom3, then by all means waste your money. If you just want bragging rights, by all means, waste your money. If you are really concerned about real-world performance, use the Performance Database, and some common sense, to figure out what drive and controller combo is really worth it.

(Sorry for the possible rudeness, but sometimes you need a dose of reality.)

Share this post


Link to post
Share on other sites
If it will be primarily a gaming machine, the Maxtor Atlas 15k and Fujitsu MAS are only slightly ahead of the significantly cheaper to implement Raptor 74.

Not to mention that an i875P board, which has onboard SATA that isn't restricted by the PCI bus, actually costs less than a U320 and many U160 host adapters (assuming that one already has a P4 system).

Yes, a single Raptor 74 won't exceed 32 bit PCI by itself, but 2 drives are better than one (split pagefile etc.) and even with only one drive, you still have to consider that the network, sound card etc. have to share the PCI bus.

KC

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now