• Updated 2023-07-12: Hello, Guest! Welcome back, and be sure to check out this follow-up post about our outage a week or so ago.

Powerbook G3 SCSI interface speed?

avadondragon

Well-known member
Does anyone definitively know what type of SCSI the Powerbook G3's use and how fast it is? I'm guessing narrow SCSI-2 at around 5MBps?
 

Phipli

Well-known member
Does anyone definitively know what type of SCSI the Powerbook G3's use and how fast it is? I'm guessing narrow SCSI-2 at around 5MBps?
Weird. It doesn't say in the spec sheet, developer notes or user manual. I'd assume 5MB/s because they only put faster SCSI in machines where it was the primary disk interface. Even the 8600, one of the busses is only 5MB/s.

Is it SCSI-2 if it is 5MB? Or would that make it vanilla SCSI? I don't know.
 

avadondragon

Well-known member
Yeah I looked all over and couldn't find the tech specs for it. I'm finding conflicting info on Mac SCSI speeds and what they're calling SCSI-2 versus 'fast' SCSI.
 
Last edited:

Phipli

Well-known member
Yeah I looked all over and couldn't find the tech specs for it. I'm finding conflicting info on Mac SCSI speeds and what they're calling SCSI-2 versus 'fast' SCSI.
Apple only used 5 and 10MB scsi built in that I know. Technically 5 is SCSI1 and 10 would be SCSI2... but it practically makes no difference and those names just relate to what standard it was defined in, not what form it takes or connectors, or even bus width or anything. Just consider it 5 and 10MB/s.
 

Phipli

Well-known member
To be honest, I'm trying to not say things that I don't know for sure, but I'd eat my own foot if it isn't 5MB/s "narrow", bog standard SCSI-1.

Can I ask why you're asking?
 

avadondragon

Well-known member
My understanding is that ALL external SCSI connectors on Macs are 5MB/s. (or slower on old Macs)
The only 10MB/s SCSI are internal on most PCI PowerMacs plus or minus a couple models.

I'm playing with my PiSCSI and was wanting to know for benchmarking purposes. I guess I'll have to crack open one of the old PowerMacs if I want to test higher speed SCSI. Just curious if PiSCSI can deliver enough performance to notice a difference.
 

avadondragon

Well-known member
I was looking at the PowerBook G3 tech notes for other reasons and accidentally came across this line:

"SCSI controller implemented using the Mesh design"
 
Last edited:

ArmorAlley

Well-known member
I'm not sure how helpful this is, but Adaptec have a PCMCIA SCSI card (with a very flimsy adapter) that will work with the PB G3.
 

trag

Well-known member
Apple only used 5 and 10MB scsi built in that I know. Technically 5 is SCSI1 and 10 would be SCSI2...

[]NITPICK] That's not really true and has caused no end of confusion. SCSI 1 and SCSI 2 are revisions of the SCSI standard, although it's arguable that SCSI I never existed or was never codified.

Unenhanced SCSI 1 and SCSI 2 are both capable of 5 MB/s performance, in theory. The SCSI 2 standard offered (optional) enhancements that allows SCSI to operate at 10 MB/s (Fast or Wide) or 20 MB/s (Fast and Wide both together). In the wild you never see Wide without Fast, but according to the Standard, it could exist.

So, anyway, to say something is SCSI 2 doesn't really tell you anything about the data rate other than that it is 20 MB/s or less. If could be 5, it could be 10. [/NITPICK]

On Apple's implementations, if there was an external SCSI port, the speed was always 5 MB/s. I suppose I should nitpick myself here, as that's only true for external SCSI ports built into machines. If the port was on a card, Apple offered faster SCSI options on some models, then it might be faster. But it is also the case that most of the time when Apple offered an installed faster SCSI card option, they did everythign they could to block off (or omit entirely) the external SCSI port on the card.

According to the Apple Developer Notes the PowerBook G3 (depending on model) had either a Heathrow I/O Controller or a O'Hare I/O Controller. The SCSI port comes from the hardware in the I/O controller. Beige G3 computers had Heathrow. PowerMac 5500/6500 had O'Hare.

In either case, the SCSI port(s) only supported 5 MB/S.
 
Top