Which is faster on my Beige SCSI or IDE

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macintoshme's picture
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Which is faster on my Beige SCSI or IDE
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Onboard ATA buses are faster...

than the onboard SCSI, ATA = 16MB/s vs. SCSI 5MB/s.

dan k

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I'd Say IDE...

My old beige G3/333 tower (OS 9.2.1) came with a fast SCSI card and matching 9GB drive, and I always thought it was a bit slow. I had a 60GB ATA drive in it for extra capacity, and once I had copy the System Folder over to boot it from that drive for some diagnostics on the SCSI, and was shocked at how much snappier the machine was when using that drive. Not sure what to attribute that to, but it was enough to convince me that the 9 gig drive should be back-burnered.

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Beige G3: onboard internal SC

Beige G3: onboard internal SCSI is 10mbs tops, onboard ATA is 16mbs tops. But the stock ATA drive was 5400rps. If you were to put a 10k rps SCSI harddrive on the onboard SCSI port, then...well, you'd have to do speed tests, but the better solution is certainly to get a third party PCI SCSI or ATA controller card.

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re: Beige G3: onboard internal SCSI is 10mbs tops

I've seen this misconception many times, however it ain't so.

...supports a maximum data transfer rate of 5 MB per second
My own observations confirm this. Also, the OEM ATA HDs are 4200 RPM, not 5400. Main page of the devnote can be found here.

First time I stuck a fast ATA drive in a Gossamer I was blown away by how fast it is. Unless you have some reason to be dissatisfied with the onboard ATA I'd stick with that. With such a relatively slow machine, a fast PCI-ATA adapter won't be an enormous improvement.

dan k

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The full quote is: "The exter

The full quote is: "The external connector supports a maximum data transfer rate of 5 MB per second. The internal and external SCSI connectors share the same SCSI bus."

The internal and external share the same bus, but I've read so many times on specs pages that the internal is 10mbs while the external is 5mbs. I believe it is related to the external DB25 connector which can only do slower speeds. If this is incorrect, I'd surely like to know, since I seem to have noticed the difference in speeds external and internal myself, but I never did actual speed tests.

But I recently picked up a Beige for a friend which still had the stock HD in it, and I put an Adaptec 40 SCSI card in it with a 10k SCSI HD, and the speed increase over the stock ATA was phenomenal.

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re: The full quote is: "The external connector

Blum 3 Bus speed is the same no matter the connector. I didn't include that part of the quote for the very reason that some folks get . . . errr, confused. Blum 3

If you doubt me, test it. Find a SCSI drive capable of better-than-5MB/s data transfer, and try it on both internal and external connectors. You'll find the data rate identical either way.

I think many folks confuse the Gossamer with the earlier 2-bus PCI Macs, where the internal-only bus is 10MB/s and the shared internal/external bus is 5MB/s. I think many find it implausable Apple would remove 10MB/s support from a later Mac.

In any case, I think we can agree a fast ATA drive will saturate the internal ATA buses, and that's much faster than almost any SCSI drive smaller than say, 18GBs, or slower than 10K, and certainly faster than anything on the internal SCSI bus.

dan k

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Old Mac Myths

Hmm, that would be interesting, since all the Powersurge Macs (7200-9600) have shared internal-external SCSI busses, don't they? And their stock HD's were SCSI. According to Low End Mac, the 9600 does 10mbs internal, 5mbs external:

http://www.lowendmac.com/ppc/9600.shtml

Is this the myth proliferated, or am I wrong about them sharing the bus? Sure looks like they share the bus just by looking at the motherboard.

The same question was just recently asked on another forum site:

http://forums.dealmac.com/read.php?4,2525948,2525948

No one was clear there either. But if you look at the bottom of LowEndMac's page about the Beige G3:

http://www.lowendmac.com/ppc/g3.shtml

There's a discontinued link there called "Slower than expected SCSI (MacInTouch Special Report)" which sounds like it may have supported your position.

Another old Mac question. Speaking of which, I'm still waiting for someone to post of picture of the mythological PM9600 560W power supply. These old myths are still hanging about unconfirmed.

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2 scsi buses

The PCI Macs (excepting the 7200) have 2 separate buses, the Fast SCSI bus (bus 0) which comes off the MESH chip, and the 'slow' bus (bus 1) which is on the Curio chip. There are separate internal connectors for both, but only the slow bus has an external connector. Run ASP, you'll see.

I routinely use both internally, usually putting the optical on the slow bus to keep the Fast bus clear for those zippy-hot 10K jobbies of which I still have a stack. Blum 3

Read the devnotes, eh?

dan k

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Will do.

Will do. Thanks, I've never seen the devnotes before. Never popped up in my Google searches. And yes, I forgot about the two SCSI buses on the 9600. Was a problem figuring out which was which sometimes. This is how you learn things sometimes, ask uninformed questions or post uninformed remarks and let you guys correct me. Thanks again.

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im running my AIO with just a

im running my AIO with just a standard 15gb maxtor 5400 rpm drive and i am more than impressed with its performance.

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Dan K. is Right

The PCI Power Macs (7200-9600 series) have two SCSI busses, with the internal one maxed out at 10MB/sec and the external one (or external/internal as Dan says - I didn't know the external bus also had an internal mobo connector) limited to half that. My old 7300 definitely had SCSI buses 0 and 1, and the speed difference was pronounced.

But the beige G3s have only the one, slower bus - no doubt to save money since their hard drives were ATA, and since SCSI drive-equipped models came with much faster Ultra SCSI PCI cards installed.

For a beige G3, a 7200rpm - or even 10k rpm - SCSI drive isn't going to help much, because they'll still be limited by the speed of the SCSI bus. So I'd say even a 5400rpm ATA drive is going to work faster than any SCSI drive unless you install a PCI SCSI card. (I didn't know that stock ATA drives were shipped that only did 4200rpm - although when I upgraded the SCSI drive in my 7300 to a 7200rpm model, I was shocked to learn that the stock drive had been only a 4500rpm model - I'd assumed it was 5400rpm.)

Finally, given what I've read about SCSI under OS X, I would imagine an ATA drive would be easier to live with if you're running X on that beige G3.

Best,
Matt

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Re: Dan K. is Right

Finally, given what I've read about SCSI under OS X, I would imagine an ATA drive would be easier to live with if your're running X on that beige G3

Heh, I got a 2GB Jaz drive working under OS X, i was surprised that it work. I didn't really have a connector to do the external, but used an extended internal one routed thru the PCI Slot, and hooked it to the jaz drive. Then I use a self-rigged Power supply to supply power. Needless to say, I was unimpressed with the performance compared to the internal ATA.

BTW: Tiger runs like a charm on the AIO's. Even with the paultry 256MB I have in my machine Blum 3

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Re: re: The full quote is: "The external connector


I think many folks confuse the Gossamer with the earlier 2-bus PCI Macs, where the internal-only bus is 10MB/s and the shared internal/external bus is 5MB/s. I think many find it implausable Apple would remove 10MB/s support from a later Mac.

I'm late to the party, but just wanted to chime in that Dan K has it exactly right and add a bit more explanation and an observation.

I have a friend who worked in Power Computing Tech Support. He says that the reason that the external SCSI busses are only 5MB/s is to make support easier. Apple's belief was that the tighter cabling specifications for 10 MB/s SCSI would cause user problems and so they should make all external SCSI 5 MB/s. The SCSI specification calls for shorter maximum cable lengths for Fast SCSI than for 5 MB/s unenhanced SCSI. Presumably this is also why later OEM SCSI cards included by Apple in their machines had the external connector omitted or covered.

(All Apple external SCSI busses were actually external/internal except on the Q900/950 and the Mac Plus, but I use "external" here for convenience. External/internal, means that one bus had both internal and external connectors.)

It would not have cost any more (for hardware) for the Beige G3 to have 10 MB/s. The SCSI logic is built into another chip (Heathrow) on the G3 and the chip real estate difference isn't noticable between slow and Fast SCSI. There may have been a licensing cost difference. It's unclear whether they had to license the 53CF96 logic in the MESH chip or not.

I've seen the 5MB/s SCSI bus reported as a 53C94 and a 53C96 but those are very similar chips so it isn't surprising that software can't figure out which one is hidden in the Apple chip.

Anyway, the point is that the 53C family of SCSI chips was already old when the Beige G3 was designed and using one variant over another (53C96 vs. 53CF96) wasn't going to make any significant difference in cost. This family of chips is so old that at least three manufacturers were producing it (AMD, Zilog, NEC/SymBIOS/LSI Logic). AMD incorporated the 53C94/96 into their Curio chip, which is where the slow SCSI resides on the x500/x600 machines (and on the X100 machine).

In fact, it's entirely possible that the SCSI implementation in Heathrow is a 53CF96 (MESH equivalent) and they just have the Fast feature disabled--interesting hacking possibility there.

So it wasn't hardware cost that drove slow SCSI in the Beige. It was imagined support costs.

Much of the confusion regarding the Beige's SCSI occurs because the SCSI bus is SCSI-2. That is, it meets, or was reported to meet, the SCSI-2 specification. Many folks assumed that SCSI-2 was synonymous with Fast SCSI. This is not the case. Before the SCSI-2 specification was prumolgated there really wasn't an accepted SCSI specification in the industry. So the SCSI-2 specification was agreed upon and published and one of the things it included was the specification for Fast SCSI and Fast & Wide SCSI. However, it also included unenhanced (neither fast nor wide) SCSI.

The Beige G3 has *unenhanced* SCSI-2. That is, slow SCSI. But you will find actual paper publications that had real subscribers with articles claiming that the Beige G3 has 10 MB/s SCSI.

Finally the observation. This has been touched on earlier by others. It doesn't do much good to have a fast bus if your hard drive is slow. Just because the electronics on a hard drive can communicate at a certain rate doesn't mean that the platters and heads on the drive can sling data at that rate. The hard drives shipped with the Beige G3 were mostly abysmally slow.

Any drive released in the last 5 years will deliver data fast enough to saturate the busses on the G3, but earlier drives may not, depending on model.

So, the ATA drives included on the Beige G3 aren't much faster than the 5 MB/s speed of the SCSI bus. Put a newer drive on there and you'll get something much closer to the ATA bus's 16 MB/s and it will be noticable.

Modern ATA drives easily deliver 40 MB/s (but notice that their electronic interface is rated at 133 MB/s) or more, so to really take advantage of new drives, add an ATA-66 or faster card. The ATA-133 cards support drives larger than 137 GB and the older cards mostly don't, so if you're buying a new large ATA drive, it makes the most sense to get an ATA-133 card such as the Acard 6280M. Fry's had a 250 GB drive for under $70 this week. Smile

But even with an older drive, but not as old and slow as the Apple included drive, you'll see a nice performance improvement on the built-in bus.

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Re: re: The full quote is: "The external connector


I think many folks confuse the Gossamer with the earlier 2-bus PCI Macs, where the internal-only bus is 10MB/s and the shared internal/external bus is 5MB/s. I think many find it implausable Apple would remove 10MB/s support from a later Mac.

I'm late to the party, but just wanted to chime in that Dan K has it exactly right and add a bit more explanation and an observation.

I have a friend who worked in Power Computing Tech Support. He says that the reason that the external SCSI busses are only 5MB/s is to make support easier. Apple's belief was that the tighter cabling specifications for 10 MB/s SCSI would cause user problems and so they should make all external SCSI 5 MB/s. The SCSI specification calls for shorter maximum cable lengths for Fast SCSI than for 5 MB/s unenhanced SCSI. Presumably this is also why later OEM SCSI cards included by Apple in their machines had the external connector omitted or covered.

(All Apple external SCSI busses were actually external/internal except on the Q900/950 and the Mac Plus, but I use "external" here for convenience. External/internal, means that one bus had both internal and external connectors.)

It would not have cost any more (for hardware) for the Beige G3 to have 10 MB/s. The SCSI logic is built into another chip (Heathrow) on the G3 and the chip real estate difference isn't noticable between slow and Fast SCSI. There may have been a licensing cost difference. It's unclear whether they had to license the 53CF96 logic in the MESH chip or not.

I've seen the 5MB/s SCSI bus reported as a 53C94 and a 53C96 but those are very similar chips so it isn't surprising that software can't figure out which one is hidden in the Apple chip.

Anyway, the point is that the 53C family of SCSI chips was already old when the Beige G3 was designed and using one variant over another (53C96 vs. 53CF96) wasn't going to make any significant difference in cost. This family of chips is so old that at least three manufacturers were producing it (AMD, Zilog, NEC/SymBIOS/LSI Logic). AMD incorporated the 53C94/96 into their Curio chip, which is where the slow SCSI resides on the x500/x600 machines (and on the X100 machine).

In fact, it's entirely possible that the SCSI implementation in Heathrow is a 53CF96 (MESH equivalent) and they just have the Fast feature disabled--interesting hacking possibility there.

So it wasn't hardware cost that drove slow SCSI in the Beige. It was imagined support costs.

Much of the confusion regarding the Beige's SCSI occurs because the SCSI bus is SCSI-2. That is, it meets, or was reported to meet, the SCSI-2 specification. Many folks assumed that SCSI-2 was synonymous with Fast SCSI. This is not the case. Before the SCSI-2 specification was prumolgated there really wasn't an accepted SCSI specification in the industry. So the SCSI-2 specification was agreed upon and published and one of the things it included was the specification for Fast SCSI and Fast & Wide SCSI. However, it also included unenhanced (neither fast nor wide) SCSI.

The Beige G3 has *unenhanced* SCSI-2. That is, slow SCSI. But you will find actual paper publications that had real subscribers with articles claiming that the Beige G3 has 10 MB/s SCSI.

Finally the observation. This has been touched on earlier by others. It doesn't do much good to have a fast bus if your hard drive is slow. Just because the electronics on a hard drive can communicate at a certain rate doesn't mean that the platters and heads on the drive can sling data at that rate. The hard drives shipped with the Beige G3 were mostly abysmally slow.

Any drive released in the last 5 years will deliver data fast enough to saturate the busses on the G3, but earlier drives may not, depending on model.

So, the ATA drives included on the Beige G3 aren't much faster than the 5 MB/s speed of the SCSI bus. Put a newer drive on there and you'll get something much closer to the ATA bus's 16 MB/s and it will be noticable.

Modern ATA drives easily deliver 40 MB/s (but notice that their electronic interface is rated at 133 MB/s) or more, so to really take advantage of new drives, add an ATA-66 or faster card. The ATA-133 cards support drives larger than 137 GB and the older cards mostly don't, so if you're buying a new large ATA drive, it makes the most sense to get an ATA-133 card such as the Acard 6280M. Fry's had a 250 GB drive for under $70 this week. Smile

But even with an older drive, but not as old and slow as the Apple included drive, you'll see a nice performance improvement on the built-in bus.

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