White Papers Advantages of AdvanSys SCSI cards In this memo, three topics are discussed: 1.What are the advantages of ABP940UW, an ultra wide SCSI adapter? 2.Why ABP930UA, an ultra SCSI adapter, still is the best I/O attachment solution? 3.ABP916, a low-cost bus master adapter, the perfect solution for CD-R attachment. ConnectCom Support: White Papers Advantages of AdvanSys SCSI cards In this memo, three topics are discussed: 1.What are the advantages of ABP940UW, an ultra wide SCSI adapter? 2.Why ABP930UA, an ultra SCSI adapter, still is the best I/O attachment solution? 3.ABP916, a low-cost bus master adapter, the perfect solution for CD-R attachment. The memo is organized first discussing the ABP940UW and why high-end workstations and file servers are using SCSI. With Windows95 any one who has multiple active windows and works with large amounts of multimedia (A/V, or audio/video) data or CD-R mastering should also consider the ABP940UW. I also discuss that with an affordable price from AdvanSys, why folks without the fastest PC can still use the ABP930UA. Finally, for the system integrator of CD-R devices, why ABP916 is a good solution. ABP940UW, The Best Price/Performer For A High-Speed PC The difference between ABP940UW and ABP930UA is that the former doubles the maximum data transfers from multiple I/O devices to 40 megabytes per second and the latter is capable of 20 megabytes per second. The main issue to be addressed is that for a sophisticated user with a high-speed PC doing video data capture and editing with DVD and CD-R devices does he need SCSI ultra-wide devices or only EIDE devices? To start, first and foremost, lets deal with the performance difference between 33 megabytes/sec EIDE and SCSI devices by referring to a paper at: http://www.adaptec.com/pdfs/scsiv_udma_wp.pdf that disputes the misleading performance data produced by people promoting EIDE devices. In fact, the biggest lie of the PC industry, is trying to make the novice users believe that the EIDE device can transmit 33 megabytes per second of data from a hard disk while an ultra SCSI device can only do 20 megabytes/sec. While this is theoretically possible, both EIDE and SCSI disk drives can only sustain at most 14 megabytes of data per second continuously which is the maximum speed of data coming off the hard disk media. Therefore, the 33 megabytes/sec EIDE device being faster than an ultra SCSI device is just smoke and mirrors. For most application software, the amount of data from each disk drive is only a few megabytes per second. The main difference between EIDE and SCSI is that the EIDE attachment can only make one device, either it be hard disk or CD-ROM, active at a time. The SCSI attachment can make many devices run concurrently. With aggregated data transfers from multiple disk devices there is a higher overall data transfer rate. The continuing adoption of SCSI devices by file server and high-end workstation communities who use multiple I/O devices provide the best testimony that SCSI attachment is much better than EIDE. For the power users with a fast PC, the only question we need to answer is "When should a user consider the ABP940UW adapter with multiple ultra or ultra-wide SCSI devices instead of several EIDE devices?" In Windows95, if a user presses the CTRL-ALT-DEL keys, he can see all the outstanding tasks running. Most of us are surprised that so many tasks are active even we have no active windows opened. This is because Windows95 is like our government. It provides all kinds of services even you never demand them. Each time a new window is opened many more active tasks are added. For some of us, we have many active windows opened at the same time. To accommodate all these active tasks which can not all fit inside the system memory, Windows95 must use a swap file on a hard disk to swap out any tasks that temporarily become inactive. It should be obvious to the readers that the more memory they have the less swap activities for Windows95. Now lets check a real desktop environment. Say, a user starts Netscape Browser to log into the Yahoo chat room, starts another Netscape HTML Page Composer to take notes, and he also opens the Netscape Message to monitor his incoming emails. By the way, this is exactly what this author is doing at this very moment. The Netscape Browser has its own disk caching and swap files, the page composer needs to write the file to a hard disk, and, finally, the incoming emails are also saved to another hard disk file. Suddenly, there are four concurrent disk activities happening: the system swap file, the internet browser page and file caching, the saving of data by page composer, and the saving of incoming emails by Netscape Messenger. Needless to say, the system swap I/O activities are running concurrent with your active task, whether it is Page Composer, Word, Excel, or CD mastering. If one does the CD mastering by reading from a hard disk continuously and writing to a CD-R, he adds two more streams of I/O activities to his computer. More active tasks mean more concurrent disk activities. The EIDE disks on one cable can only do one disk I/O task at a time. Therefore, all those disk activities are done in serial. File copy creates two sets of activities: reads and writes. Most computers today have one hard disk and one CD-ROM each on a separate EIDE cable. This is a poor-man˙s way of doing minimum concurrent I/O activities without a multitasking SCSI adapter. In this configuration we are sharing all system swap, Netscape caching, and CD mastering disk I/O˙s on the same hard disk. Everything is done in serial. No wonder all CD-R manufacturers carefully ask you to shut down all other tasks while mastering a CD to ensure the system disk not becoming too busy. If it does, you have a good chance of underruning the writing of the CD-R which is a very nasty thing. The cheapest way to improve the system performance is spread the concurrent disk activities to separate disks using a multitasking and low-cost SCSI adapter like the ABP940UW or ABP930UA. Below, we will discuss when do you need an ABP940UW instead of an ABP930UA. Today, the maximum data rate from each disk is below 14 megabytes per second. However, the average data to each disk is normally only 2 to 3 megabytes per second. Therefore, normally, an ABP930UA will be sufficient to handle 2 to 3 SCSI devices concurrently. However, for users with video data capturing and editing, the instantaneous data rate from a disk of 10 or more megabytes per second is very critical. This is why they need an A/V certified disk that will never stray away during normal data transfers. To ensure two disk drives both sustaining the maximum data rate, you need a bus master SCSI adapter with greater than 20 megabytes per second of data rate. Two ultra wide devices with an ABP940UW become necessary. By the way, two EIDE devices on two EIDE connectors will do the same trick ˙ assuming you got the EIDE bus master driver installed, which is generally untrue for most PCs. However, with two EIDE hard disks, you have a different problem, where do you connect the CD-ROM? If the CD-ROM is sharing a connector with one of the two hard disks, each time the CD-ROM spends over 100 milliseconds moving its access arm, the hard disk is totally blocked out because there is only one EIDE device active on each EIDE cable. By the way, you know what I am talking about just by imaging driving behind a truck on an uphill climb. There is no such problem for SCSI devices connecting to a bus master SCSI adapter because it works like a multiple-lane highway. You simply switch lane to pass the truck. In conclusion, if video data editing is your hobby or you need to keep two hard disks both sustaining more than 10 megabytes per second of data rates, the ABP940UW will be a good choice for you. Or, if you like to keep many active windows open for several streams of disk I/O activities, you should get those ultra wide devices and adapter. By opening many windows you are now officially qualified as a ˙power user.˙ ABP930UA, The Best I/O Attachment Solution For all practical purposes, ABP930UA is a functional equivalent to the AHA2940U from Adatpec with only one third of the price to OEM customers. The performance of ABP930UA is equal to if not better than that of AHA2940U. This can be easily proven with the multi-threaded benchmark, WinIO, from Adaptec or the Intel benchmark, IoMeter. However, the real question we need to answer is why should an end-user pay $70 to $100 for ABP930UA instead of using an EIDE device which requires no adapter at all. As we have discussed before, we don't need to justify that SCSI is better than EIDE in the file server and high-end workstation environment in which computer professionals are happy to pay $200 or more to buy SCSI adapters and the extra costs for SCSI devices. AdvanSys has a special sales program with Microsoft. Many professionals from Microsoft have bought SCSI adapters directly from AdvanSys. Why should a non-power user need a multitasking SCSI adapter? How about the end users who do not have a high-end workstation, is the EIDE attachment sufficient? If a user is still running Windows 3.1 or only working with one window under Windows95 at a time, then, the user may be happy with the EIDE disk drives. For those users who download files from the internet, scan a long document, or do a large file backup or copy, they simply sit back and stare at the screen without doing anything, then, EIDE devices may be adequate. On the other hand, if a user becomes more comfortable with Windows95, during the copy of large files or directories, he would like to switch to another window to compose or read an email or prepare a spreadsheet. In other words, if one prefers to have several windows active under Windows95, he should have the ABP930UA. The main difference between SCSI and EIDE is multitasking versus single tasking. In a file server and high-end workstation there are always many tasks running at the same time. This is why they will not use EIDE devices that can only service one I/O request efficiently at a time. What novice users do not aware was that Windows95 has many tasks running in the background and very capable of supporting multiple concurrent tasks. Whether you are a computer professional using high-end workstations or not, if you have more than one window opened and would like to move the mouse among different windows often, you should have the ABP930UA adapter. We have already discussed the system swap files and internet page and file caching function previously. In addition to attaching multiple devices, SCSI adapters are also for external devices. EIDE is only for attaching internal devices. Once we have a SCSI adapter in our computer, we can connect scanner, CD-ROM, tape, DVD, or an Iomega ZIP device to the external SCSI connector. Simply by telling Windows95 to refresh -- a function available in Windows95 under device manager of the SYSTEM icon -- magically, the new SCSI device is instantaneously visible to the computer and available to the users without any hassles at all. Most computer professionals connect an Iomega ZIP and JAZ drive to their external SCSI connector to copy a few hundred megabytes of video data from or to the computer. Parallel port is simply too slow for files with megabytes of sizes. This refresh function is not available to EIDE device or devices attached to a parallel port. As an alternative to the SCSI connection, external devices can be attached to a parallel port with very slow data transfer if we can tolerate the difficulty of having multiple devices on the same parallel port each with a different device driver. Putting external devices on parallel port is only reserved for those who simply too timid to open the computer chassis. In their timid minds, slow data transfer is only a necessary evil. Installing an EIDE or a SCSI adapter requires a user to open the computer chassis. To overcome this fear, AdvanSys provides an installation program, SuperSCSI, to make the installation of ABP930UA a refreshing experience. In the old days installing a SCSI adapter means pain and confusion and should be left only to computer professionals. The Intel PCI plug-and-play function and the accumulated experiences of installing SCSI devices in the last ten years have changed the landscape totally. Today, with SuperSCSI a user can install a SCSI adapter without knowing what he is installing. Run the SuperSCSI CD prior to adding the SCSI card to the system. Everything is prepared before hand. Power off the computer, add the SCSI card and device, and power the computer on again. After finding the new adapter and all the corresponding device drivers, Windows95 simply informs the user that everything is OK and the new SCSI adapter and its devices are ready to go. If, in rare cases, the user did not connect the cable correctly, SuperSCSI will help the user to correct the problem without digging into Windows95 to find the problem. One retail channel reported that while there was a 15% return of an IDE device, only a 3% return rate for the corresponding SCSI device. In addition to making the scanner run faster and writing the CD-R without data underrun, the multitasking ABP930UA is ideal for Windows95 users because of the system swap activities happening during the mastering of a CD. The users have to remember that the ABP930UA can deliver 20 megabytes of data per second from multiple I/O devices concurrently. This assures the CD-R writing not interrupted by other I/O activities started by other tasks under Windows95. This also assures the high-speed scanner does not slow down by the same. For a fraction of the price paid by computer professionals, a Windows95 user can enjoy the same performance benefit from a SCSI adapter as that enjoyed by professionals with high-end workstations and file servers. ABP916, The Best Solution For A CD-R Device Realistically, ABP940UW is for power users and ABP930UA is for folks with many active windows. If one only wishes to ensure his CD-R writing successfully with minimum chance of data underrun, then, the ABP916 can be a very good low cost solution without sacrificing the data transfer performance. The ABP916 can sustain 10 megabytes per second of bus master data transfer. Bus master means that during data transfer the CPU is freed to collect more data from hard disk for writing to the CD-R. Most CD-R devices or scanners are moving data in less than few megabytes per second. Since most computers have one EIDE hard disk and one CD-ROM connected to two separate EIDE cables, there is no good place to add the CD-R. As we have stated repeatedly, the EIDE connection allows one I/O activity at one time. If the CD-R is sharing the cable with the hard disk, the reading from hard disk will be blocked whenever the software writes to the CD-R not to mention the system swap file activities. If we allow the CD-R sharing the cable with the CD-ROM, even by ensuring the CD-ROM staying idle while the CD-R is busy, we are still faced with another EIDE problem. We must have the bus master driver installed for the EIDE device. As we stated earlier, most computers today do not have the driver installed because of compatibility issue with many EIDE devices, i.e. not all EIDE devices do bus master transfer correctly. No such problem for SCSI devices. Without the bus master driver, the CPU of the computer must manually move the data on both reading from the hard disk and writing to the CD-R. The CPU itself is used serially which prevents the hard disk and the CD-R from running concurrently. We are back to the scenario of driving behind a big truck on an uphill climb. The hard disk is as slow as the CD-R because the CPU can not take care of the hard disk when it works with the CD-R. In conclusion, the safest way to connect the CD-R is to use a bus master SCSI adapter like the ABP916 and leave the CPU to manage the hard disk reading and leave the CD-ROM with its own EIDE connection. The bus master data transfer of the ABP916 ensures the writing to the CD-R is not interrupted while the CPU reads from the hard disk continuously. Of course, the user must minimize the system swap activities by shutting down as many tasks as possible because the swap activities prevent the CD-R mastering software from reading the same hard disk. Getting a second hard disk connected to the ABP916 would definitely help.