correction needed on A+ core technotes

techboyjk

technotes lists scsi ultra3 at 40mhz bus speed, where as I believe it is actually 80mhz. fyi....

Plantwiz

techboyjk wrote:

technotes lists scsi ultra3 at 40mhz bus speed, where as I believe it is actually 80mhz. fyi....

I just reviewed pg 597 of Mueller's "Upgrading and Repairing:16th edition"

Ultra3 - pulished on 11-1-2000, and build on previous standard primarily by doubling the speed to FAST-80DT (double transition). The results in maximum throughput of 160MBps.

DT clocking sends data on both the rising and falling edges of teh REQ/ACK clock. This enables Ultra3 SCSI to transfer data at 160MBps, while still running at a bus clock rate of 40MHz. This mode is defined for 16-bit wide bus use only

Looks like the notes are correct. Perhaps Johan, will review this soon.

caustik

i noticed that too

p869 in mike meyers 5th A+ aio lists it as 80 mhz aswell no mention of
double data rate

Webmaster

where as I believe it is actually 80mhz. fyi....

I certainly don't mind any questions about my TechNotes (though I'd prefer a different subject for the topic if you believe something is incorrect), but you'll have to do better than that, ie. list several sources that confirm your claim. Most of the time in writing the TechNotes goes into fact-checking and research. Even if I think I know it from the top of my head, I make sure I can back it up with several reputable sources, which does not include any certification/study material as inaccuracies in those is one the reason I started writing in the first place. In other words, I don't just make things up

Having said that, I'm only human, I do make mistakes. And although the topics in the A+ TechNotes still apply, they do need an update. The SCSI notes are from October 11, 2003 for example. I remember I found an exceptional amount of conflicting resources when I wrote the SCSI notes (which made writing the notes more challenging and interesting as well). A quick search on google shows indeed that there are some resources who claim Ultra3 is 80Mhz... The trick is to separate the dubious sources from the reputable ones. (regardless of the previous post I consider Mike Meyers to be one of the latter.) Or in this case, the incomplete from the complete.

One reason why you will be able to find different values for Ultra3 is because not all Ultra3 products are the same (not all SPI-3). In short: all SPI-3 SCSI devices are Ultra3, but not all Ultra3 devices comply with SPI-3. Another reason is of course the fast-dt80 feature, as Plantwiz quoted and is also explained on: www.pcguide.com/ref/hdd/if/scsi/std/scsi3SPI3-c.html for example.

The table in my SCSI TechNotes explicitely mentions 40 Mhz for Ultra3(just a marketing term from www.scsita.org*, not a specification)
using the SPI-3 specification hence is accurate and does not need correction.

If that still leaves doubts, according to the official standard SPI-3 is 40Mhz.

www.t10.org/scsi-3.htm
www.t10.org/drafts.htm#spi3

I hope this clears it up, let me know if you have any more questions/comments.

Plantwiz

I see Johan posted while I was looking for additional resources

I also found this:

SCSI Bus Speed

Scroll down near the bottom - you can review a comparison chart.

caustik

so on the test the answer should be 40 mhz ?

caustik

this is from the same page plantwiz suggested but a more complete chart:


http://www.storagereview.com/guide2000/ref/hdd/if/scsi/summary.html


just what i needed

techboyjk

Webmaster wrote:

where as I believe it is actually 80mhz. fyi....

I certainly don't mind any questions about my TechNotes (though I'd prefer a different subject for the topic if you believe something is incorrect), but you'll have to do better than that, ie. list several sources that confirm your claim. Most of the time in writing the TechNotes goes into fact-checking and research. Even if I think I know it from the top of my head, I make sure I can back it up with several reputable sources, which does not include any certification/study material as inaccuracies in those is one the reason I started writing in the first place. In other words, I don't just make things up

Having said that, I'm only human, I do make mistakes. And although the topics in the A+ TechNotes still apply, they do need an update. The SCSI notes are from October 11, 2003 for example. I remember I found an exceptional amount of conflicting resources when I wrote the SCSI notes (which made writing the notes more challenging and interesting as well). A quick search on google shows indeed that there are some resources who claim Ultra3 is 80Mhz... The trick is to separate the dubious sources from the reputable ones. (regardless of the previous post I consider Mike Meyers to be one of the latter.) Or in this case, the incomplete from the complete.

One reason why you will be able to find different values for Ultra3 is because not all Ultra3 products are the same (not all SPI-3). In short: all SPI-3 SCSI devices are Ultra3, but not all Ultra3 devices comply with SPI-3. Another reason is of course the fast-dt80 feature, as Plantwiz quoted and is also explained on: www.pcguide.com/ref/hdd/if/scsi/std/scsi3SPI3-c.html for example.

The table in my SCSI TechNotes explicitely mentions 40 Mhz for Ultra3(just a marketing term from www.scsita.org*, not a specification)
using the SPI-3 specification hence is accurate and does not need correction.

If that still leaves doubts, according to the official standard SPI-3 is 40Mhz.

www.t10.org/scsi-3.htm
www.t10.org/drafts.htm#spi3

I hope this clears it up, let me know if you have any more questions/comments.

yea it makes sense. The study guide I was reading had it listed at 80mhz, cut and dry, with no mention of the extra particulars you listed. Perhaps it is technically 40mhz, but it is more common to find it at 80mhz which is why it said that? or maybe the study guide is just -1.

Webmaster

techboyjk wrote:

yea it makes sense. The study guide I was reading had it listed at 80mhz, cut and dry, with no mention of the extra particulars you listed. Perhaps it is technically 40mhz, but it is more common to find it at 80mhz which is why it said that? or maybe the study guide is just -1.

Are you referring to the same study guide as caustik? MM's AIO? It kinda works as if it is 80mhz because of the fast-DT80 feature, technically it is indeed 40mhz. I doubt it is 'more common' to find 80Mhz, at least I hope that cause they would be conflicting with the official standard. As for what CompTIA wants to hear: the general, not the exceptions. CompTIA exams are vendor neutral, so you can assume they primarily look at the standards and not at the features of a certain product of a certain manufacturer (though this is not true for the OS exam of course).

Plantwiz

caustik wrote:

so on the test the answer should be 40 mhz ?

I would answer the standard so, yes, my choice would be 40MHz.