VOGONS


First post, by p6889k

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I got me few SCSI HDDs I want to try in my Dual Pentium PRO 200 machine:

FUJITSU (MAP3735NP) 73.5GB 10K RPM ULTRA320 LVD
FUJITSU (MAN3367MP) 36.7GB 10K RPM ULTRA160 LVD
QUANTUM ATLAS 10K III, (KW36L461) 36GB 10K RPM Ultra160, not sure if it's LVD as it doesn't say on the label

I already have Adaptec AHA-2940UW and SCSI CD-ROM , ZIP and Tape Drive, but haven't used them yet as I was waiting to get some SCSI drives. Now I'm thinking whether I should change the controller to the faster AHA-2940U2W.

So, few questions:

1) Will my HDDs work with either of these two adapters? I'm not up to speed on what LVD is and whether my 10K LVD HDD would work with AHA-2940UW.
2) Is it worth going for the the faster (80MB/s) AHA-02940U2W
3) If I install Windows on AHA-02940UW, how easy is it later on switch to AHA-02940U2W? Are the drivers the same, would I need to reinstall windows? Specifically Win98, NT4, 2K.
4) Are there any compatibility issues or any other important differences between these two controllers?

It's been years since I've used SCSI, I used to have Tekram controller back in the day with 15K Cheetah's that sounded like jet engine.

Sinclair ZX Spectrum 48k, 48k+, 128k, +2
Amiga 1200, 68030/40mhz
386DX/33, ET4000, SBPro2, MT32
Dual PPro/200, Millennium II, Voodoo 2, AWE32, SC-55
etc.

Reply 1 of 7, by maxtherabbit

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Your drives will work with both, and are likely fast enough to benefit significantly from the U2W. The drivers in windows are the same, so you can upgrade later.

Ultra2, Ultra160 and Ultra320 are inherently LVD standards (low voltage differential, which is backwards compatible with traditional single ended SCSI)

Reply 2 of 7, by Woody72

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I found this thread idly searching for 2940 related threads. I recently fitted a 15k 18.2GB Seagate Cheetah and an Adaptec 2940UW into my Windows 98SE build and it couldn't have been easier. My disk speed went from 7.9MB/s to 30.5MB/s and everything runs great. Partly out of my desire to tinker, and partly because I've loved SCSI irrationally since I can remember, I've ordered a 2940U2W to see what happens and I'll update this thread. As Max said, one of the great things about SCSI is the backwards compatibility.

Modern PC: i7-9700KF, 16GB memory, RTX 3060. Proper PC: Pentium 200 MMX, 128MB EDO memory, GeForce2 MX(200).

Reply 3 of 7, by dionb

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You should see benchmark scores increase significantly - but don't expect it to feel much faster. The reason 15k drives feel so fast is their very low seek times. That's inside the drive, not dependent on controller, so not likely to change much with U2W, U160 or 320.

Reply 4 of 7, by 640K!enough

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There are a few things that are worth mentioning. Firstly, for Ultra2 and greater speeds, you generally need a twisted-pair cable rated for the correct standard or speed. As mentioned, most Ultra2 or later LVD drives are also compatible with single-ended SCSI devices and controllers, but if you mix LVD and non-LVD devices, you won't necessarily benefit from Ultra2 or greater levels of performance; the entire chain will likely negotiate single-ended speeds.

The most important point, when dealing with these devices, is that non-low-voltage differential SCSI (sometimes later referred to as HVD) devices cannot be combined on the same controller, and are not compatible. Doing this may lead damaged expensive devices.

Reply 5 of 7, by maxtherabbit

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Everyone always goes out of their way to mention HVD incompatibility issues, which is of course correct, but the truth is HVD devices were very rare and your odds of "accidentally" finding one without deliberately looking for it are slim

Reply 6 of 7, by Woody72

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You're right of course, I expect bus saturation will become more of a factor given that the card is in a PCI slot. Still fun to mess about with though 😁.

Modern PC: i7-9700KF, 16GB memory, RTX 3060. Proper PC: Pentium 200 MMX, 128MB EDO memory, GeForce2 MX(200).

Reply 7 of 7, by Disruptor

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The main difference is that the 2940U2W uses LVD transfers with 80 MByte/s. It has an external 68 pin connector and an internal 68 pin connector for LVD devices. But it also has internal 50 pin and 68 pin connectors for SE devices. The clou is the AIC-3860Q bridge that connects that 2 buses together without limiting LVD devices to fallback (SE) mode.

Extending a SCSI bus with Adaptec AIC-3860Q (2940U2W and more)

Whenever you connect SE devices to a LVD bus, all devices on that cable must use SE signaling and cannot use their higher transfer rates.
But if you use a 2940W all of your 10K and 15K disks are capped to 40 MByte/s and they easily hit this limit.

The second thing is cables and termination. LVD and SE can use twisted pair cables, but only LVD requires them.
Termination on SE buses is basically done on the devices on the endings whereas LVD buses are using a terminator on the cable. There exist SE terminators for cables too, but I recommend to use SE/LVD terminators with twisted pair cables.
And, yes, Ultra SCSI SE buses are limited to 3 meters length when using up to 4 devices including the controller. Due to minimal distance on the cable you cannot use more than 8 devices on Ultra SCSI SE buses, but up to 16 on LVD buses which are limited to 12 meters.