topic Re: SCSI Misconception in Disk

SCSI Misconception

Stefan Saliba — Wed, 21 Nov 2001 07:53:50 GMT

I want to get this misconception clear once and for all.

I read many docs on SCSI and their differences etc etc etc. I know the electrical differnece between HVD and LVD and that they should not be mixed. I also know that LVD is backward compatible with SE. My question is this,
are all FWD interfaces HVD ?

Thus is the FWD SCSI interface say on a K-class core/io HVD ? is the A4800 SCSI card an HVD card ?

Is it possible to have FWD using LVD ?

I really wish to get the concept clear once and for all

Cheers

Stefan

Re: SCSI Misconception

Alexander M. Ermes — Wed, 21 Nov 2001 11:04:10 GMT

Hi there.
Check this URL :

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0xa114cbaac6dcd5118ff40090279cd0f9,00.html

It contains two different URL's related to SCSI. Hope it is the info you need.
Rgds
Alexander M. Ermes

Re: SCSI Misconception

Jan Klier — Wed, 21 Nov 2001 17:20:32 GMT

The SCSI protocol (the physical direct attached layer) has three different attributes that describe the bus:

* width (8 - narrow, 16 - wide, 32 - not used)
* signaling (SE, HVD, LVD)
* speed (5/10/20/40)

These attributes are for the most part independent of each other and can be combined in various ways, though in terms of products several combinations have turned out to be more common than others.

FWD would refer to 'fast - 10MBit/s period', 'wide - 16 bit', and 'differential signal'.

While 'diff' commonly refers to HVDS, there is nothing that says it could be LVDS. It's more the context of the person using it, as FWD is more of a product acronym than a real standard term.

In fact I have seen many wide, LVDS interfaces that use 40 or even 80 MBit/s transfer rates (eg 39160 card from Adaptec). Note that I say MBit/s, the MB/s rate may depend on the bus width as wide busses transfer two bytes per clock cycle.

Re: SCSI Misconception

Patrick Wessel — Thu, 22 Nov 2001 19:57:49 GMT

Stefan,
Since the questions are answered in general I would like to give you an answer for your K-Class and A4800A
There is NO LVD interface for the K-Class (not on the core I/O, not as HP-PB bus interface, no HSC bus interface)
A4800A is a HVD Ultra2 card

I hope this helps