From taisung@chem.duke.edu Sat Sep 27 22:27:04 1997 Received: from chem.duke.edu for taisung@chem.duke.edu by www.ccl.net (8.8.3/950822.1) id VAA26652; Sat, 27 Sep 1997 21:56:14 -0400 (EDT) Received: from debye.chem.duke.edu (debye.chem.duke.edu [152.3.169.112]) by chem.duke.edu (8.7.4/Duke-1.1) with ESMTP id VAA28015; Sat, 27 Sep 1997 21:55:58 -0400 (EDT) Received: (taisung@localhost) by debye.chem.duke.edu (8.7.4/Duke-1.1) id VAA15678; Sat, 27 Sep 1997 21:55:56 -0400 (EDT) Date: Sat, 27 Sep 1997 21:55:53 -0400 (EDT) From: Taisung Lee X-Sender: taisung@debye To: CAVALLO@CHEMNA.DICHI.UNINA.IT cc: CHEMISTRY@www.ccl.net Subject: Re: CCL:PCI vs. SCSI and Linux In-Reply-To: <01IO4X524BR40001H3@CHEMNA.DICHI.UNINA.IT> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Dear CCLers, There is a little misunstanding in Cavallo's article. A PCI bus is a bus between CPU and the world outside it. A SCSI interface is the bridge between the system bus and your HD or other devices. You can not compare these two just as you can not say "My CPU is faster than your hard disk." Although this issue is not directly related to computational chemistry, PC's can be much cheaper choices to us CCLers. We shall to know little more about PC. A PC internal structure looks like: CPU<---L2 Cache<---Main Memory | | System Bus------------------------------ | | | | | | | | Video Keyboard SCSI IDE interface Interface , mouse.... interface | | | | Video device SCSI IDE device device To let your PC fly, the first thing to do is get a fast CPU. To do computations, Pentium Pro-200 or Pentium II's will be good choice. The second thing is get as much memory as you can. Give the current price ~$3.5 /MB, ther is no reason to cut your memory. For other parts of the system, PCI is one kind of System bus. Curreny PCI standard has highest possible bandwith of 133 MB/s in 32 bit mode and 266 MB/s in 64 bit mode. Almost new PCs come with PCI bus otherwise it is too old to keep or it is too new... We probably don't have other choices now. For people doing visualization, a good video card is necessary. Remember only get a PCI version video card. You may see 'ISA' version. ISA is old standard of system bus which has the bandwith of 8 MB/s. Most PC's keep some ISA slots. But don't buy an ISA video card or you will feel your Pentium PC is slower than a 486 when you run Rasmol. As Luigi Cavallo said, HD is another important part to look at. The most popular HDs are IDE (or its variation, EIDE and Ultra-IDE, ATA-2, ATA-3,..) HD and SCSI HD. SCSI HDs used to be much faster than IDEs. But it is not the case anymore. However, SCSI still has some advantages. We need to understand what are the factors to affect the HD performace. The first factor, of course, is the spinning speed of the HD. Most HDs has the spinning speed ~5400 RPM. High end SCSI HDs have 7200 RPM. Seagate has the fastest HD in the world with 10000 RPM. (Don't expect your workstation has better HDs than a new PC...) HDs have buffer memory to store data when do reading/writing. So the other factors will be the size of buffer memory and the data transfer rate between disks and buffer (called internal transfer rate). You sholud get a HD with buffer no less than 256KB (except IBM's, they can make very fast HD with 128KB buffer and nobody knows why...) and internal transfer rate no less than 100 Mbit/s. High spinning HDs are all SCSI (>7200RPM) but not all SCSI HDs are high spinning. Be careful about tis point. You can buy an Ultra-Wide SCSI HD with only 4500RPM ( and for sure it is slow). SCSI and IDE HD have similar buffer size and internal transfer rate. The last factor (notice: I say it is the LAST factor) is the data transfer rate between HD buffer and the system bus. It is important only when you have very slow interface or your have multiple HDs. Following is a list of maximum transfer of different interfaces: IDE: normal IDE: 5MB/s (?) ATA-2, EIDE (mode 4): 16.6 MB/s ATA-3, UIDE : 33.2 MB/s SCSI: SCSI :2.5 MB/s SCSI-2:5 MB/s fast-SCSI-2:10MB/s wide-SCSI-2:10MB/s fast,wide-SCSI-2:20MB/s ultra,wide-SCSI:40MB/s Like chemical reactions, the HD performance has a 'rate-determining' step. Say you have a HD with internal transfer rate 120Mbit/s=15 MB/s (which is very good) and you get an UW-SCSI interface and PCI system bus (133MB/s). You will find your system is not faster at all compared with a similar HD with FW-SCSI interface. If you buy an 4500RPM, internal transfer rate=50Mbit/s HD and buy an UW-SCSI card, you may just waste your money. I don't want to write too much here. To be short, don't be fooled by the bandwith of IDE and SCSI. A good EIDE HD will be as faster as a FW-SCSI/UW-SCSI HD. The HD performace of a new PC is very likely better than the workstation in your lab. However, if you want to get very very good performance, SCSI is the only way. The best HDs are still SCSI (with a doubled price). A well-develped technique called RAID allows system to write/read data to/from several SCSI HDs at the same time. Using RAID you can reach 150MB/s easily ( at that time, the PCI bus becomes the bottleneck). And you can expect 10 times more money will be gone... I already wrote too much. If there is any interest on this topic, I will post more about it. Such as the sync. transfer and multiple commands of SCSI bus. My suggestion on HD for PC. Get a new 5400RPM EIDE one and you will be happy. If you can spend at least as twice money, get a high end SCSI. my $0.02 opinion Taisung Lee > Dear CCLers, > > Recent discussions on the list "seem" to assess that the PPro 256kb > should be the best buy, in terms of performance/costs ratio. > > Anyhow, the PCs are not simply made by the CPU. We know that another > bottleneck can be the HD. A PCI bus should be more or less comparable > to a FAST SCSI 2. Better performances can be obtained on going to > Ultra Wide etc. SCSI stuff. Anyhow, prices increase. > > What the experience here ? > > Are those (more) expensive last generation SCSI pieces really needed ? > > Any comments appreciated > > Best regards, > > Luigi > > ----------------------------------- > Luigi Cavallo > Dept. of Chemistry > Univ. of Naples > Email cavallo@chemna.dichi.unina.it > ----------------------------------- > > -------This is added Automatically by the Software-------- > -- Original Sender Envelope Address: CAVALLO@CHEMNA.DICHI.UNINA.IT > -- Original Sender From: Address: CAVALLO@CHEMNA.DICHI.UNINA.IT > CHEMISTRY@www.ccl.net: Everybody | CHEMISTRY-REQUEST@www.ccl.net: Coordinator > MAILSERV@www.ccl.net: HELP CHEMISTRY or HELP SEARCH | Gopher: www.ccl.net 73 > Anon. ftp: www.ccl.net | CHEMISTRY-SEARCH@www.ccl.net -- archive search > Web: http://www.ccl.net/chemistry.html > >