Internal SCSI Bus speed

7 posts / 0 new
Last post
Offline
Last seen: 17 years 11 months ago
Joined: Mar 11 2006 - 03:16
Posts: 5
Internal SCSI Bus speed

Hi,

recently I got a IIfx on you-know-who-bay and replaced the internal HDD with a 9GB IBM DNES UW. It flies... but not as fast as I expected.
Unfortunately I have no experience with old macs and I've come to wonder if it's the bus itself. I just can't seem to get more than 700KB/s out of the drive Sad
(Benchmarking done with FWB 1.7.5)

What am I missing?

Jon
Jon's picture
Offline
Last seen: 12 years 9 months ago
Joined: Dec 20 2003 - 10:38
Posts: 2804
You'll need a NuBus SCSI card

You'll need a NuBus SCSI card to get some real speed out of the drive. The JackHammer seems to be a good choice.

Offline
Last seen: 17 years 11 months ago
Joined: Mar 11 2006 - 03:16
Posts: 5
So its true that the internal

So its true that the internal SCSI of the IIfx won't dish out more than 700kb/s?

Jon
Jon's picture
Offline
Last seen: 12 years 9 months ago
Joined: Dec 20 2003 - 10:38
Posts: 2804
The IIfx requires a specific

The IIfx requires a specific SCSI terminator to work right. It does have a custom DMA setup that should be faster than other II series Macs, but for the price of a JackHammer card, you'd likely save a lot of trouble and it'd be faster in the end. The JackHammer cards have both 50-pin narrow and 68-pin wide SCSI plugs. You just aren't going to get fast speeds out of the 50-pin IIfx port without it running in a Fast-SCSI mode. The JackHammer will at least use the drive in Wide mode, even if it might not suppor the Ultra mode.

Proper termination might speed up the SCSI bus, but it also needs to have MacOS aware of the DMA capabilties and use them. See links from http://www.lowendmac.com/ii/iifx.shtml regarding the SCSI DMA and term issues.

Offline
Last seen: 17 years 11 months ago
Joined: Mar 11 2006 - 03:16
Posts: 5
Thanks - I will take a closer

Thanks - I will take a closer look at that technote and see if I can speed things up.
What does this special 'black' terminator look like? Is it a centronics Terminator in black (I have one of those). If I remember correctly these were also calles 'active' terminators?!

Thanks.

Hawaii Cruiser's picture
Offline
Last seen: 7 years 1 day ago
Joined: Jan 20 2005 - 16:03
Posts: 1433
terminators

Yep, the external chain needs to be terminated with the special black centronics active terminator. There's also a small, thin, special black or gray plastic coupler that fits into the internal motherboard 50pin SCSI port. I don't remember if that was a terminator or not, and if so, why it would be at that junction in the chain, but some IIfx motherboards have them and some don't. Maybe someone else knows what that was for.

Jon
Jon's picture
Offline
Last seen: 12 years 9 months ago
Joined: Dec 20 2003 - 10:38
Posts: 2804
And, this [url=http://searchd

And, this old Apple TechNote mentions a bit about the IIfx SCSI speeds. Of course statement that the IIfx has the fastest SCSi bus is wrong at this point in time, but it does say that you won't get better than 3megabit/sec out of the IIfx SCSI. The NuBus has the capability of 10Mbps, so if you attach a Wide SCSI (68-pin) capable card, or even a Fast SCSI capable card, it should be to beat the stock SCSI hands down. If the card supports Wide-Fast SCSI it'll saturate the NuBus bandwidth. I'm not sure if there are Ultra capable NuBus SCSI cards (I've not looked) but even an Ultra Narrow (50-pin) should be overkill.

Log in or register to post comments