aimania@killer.DALLAS.TX.US (Walter Rothe) (11/10/88)
I was almost ready to plop my money down and get a 2090A controller until a
couple of things happened. Up til that point all the benchmarks I had seen
seemed to favor the 2090A over the other disk controllers. But there appears
to be a problem with using it with larger screen resolutions. AMAZING
computing just came out with an article that shows that the 2090A slows
way down when doing a 704 by 644 by 4 bitplane overscan display. I would
expect some slowdown since this leaves only 50 slots out of a total 226
to do all other DMA and CPU cycles during one scan line.
However, there should be plenty of time
during vertical retrace to get the needed disk activity in. Other controllers
seem to be able to do this but the 2090A does not seem to be able to use
this time. What's going on?
One of my dealers in town said the 2090A's he got shipped did not work in
interlace mode. He said they crashed the system. Could this be true?
In fairness, I should also mention that the Supra drive had some screen update
problems in the overscan mode, but it still transfered data at a respectable
rate.
Another question about the 2090A.
If you bought a SCSI disk that would spin up faster, could you use the 2090A
to autoboot or is there a hard limitation with any SCSI drive?
Anybody seen an 80meg Quantum drive for less than $1029?
Thanks Commodore for a great job on 1.3
--
Walter Rothe at the UNIX(Tm) Connection, Dallas, Tx
UUCP: {rutgers}!smu.killer.aimaniadavid@ms.uky.edu (David Herron -- One of the vertebrae) (11/11/88)
In article <6055@killer.DALLAS.TX.US> aimania@killer.DALLAS.TX.US (Walter Rothe) writes: > >I was almost ready to plop my money down and get a 2090A controller until a >couple of things happened. Up til that point all the benchmarks I had seen >seemed to favor the 2090A over the other disk controllers. But there appears >to be a problem with using it with larger screen resolutions. AMAZING >computing just came out with an article that shows that the 2090A slows >way down when doing a 704 by 644 by 4 bitplane overscan display. I would >expect some slowdown since this leaves only 50 slots out of a total 226 >to do all other DMA and CPU cycles during one scan line. >However, there should be plenty of time >during vertical retrace to get the needed disk activity in. Other controllers >seem to be able to do this but the 2090A does not seem to be able to use >this time. What's going on? I read this, saw this, and am now re-considering too ... however I do remember some talk here a little while ago saying that the problems there were driver related and that either were already fixed or were being worked on. Is my memory playing tricks on me again and this is false, or is this true? (I hope it's true). At the moment I think the only proper alternative to the 2090A, that is will give you an st506 interface as well as the scsi interface, is the er.. HardFrame(?) .. am I remembering the name right? It's the one that *wasn't* reviewed in AC. Has anybody seen one of those? Is it as good as they make it seem in the ads? >Another question about the 2090A. >If you bought a SCSI disk that would spin up faster, could you use the 2090A >to autoboot or is there a hard limitation with any SCSI drive? That's the impression I'd gotten. >Anybody seen an 80meg Quantum drive for less than $1029? Yes, I was talking with Hard Drives International this morning and the 80S (SCSI drive) is about $830 from them. Sigh, I wish I could spare enough to buy a big drive like that but I can only afford enough for about a 40 megger ... HDI advertises heavily in Computer Shopper ... Now, Quantum has a 40 meg drive just like the 80, but HDI doesn't carry it, only the 80 megger. (And the person first said that it was *only* for Mac's, and when I questioned it on her she did allow as to it could be plugged into an Amiga, but that SCSI usually means that it's for a Mac... sigh ...) For those who don't know ... the Quantum drives come in two flavors, one is an SCSI interface and the other is an "AT" interface which is probably ST506. Each flavor comes with a 64k cache on the controller board and integrated handling of bad blocks (if I'm reading the advertising right). The drive starts with a 19ms (16ms?) average access (seek?) time and with the cache enabled they claims it gets down to 11ms. This is in a 3.5 inch form factor! Now obviously there's a bit of a premium to pay for this, an 80 meg full-height seagate is running about $500 right now, versus $830 for the Quantum drive ... There's two sizes to each flavor of the quantum drive -- 40 meg & 80 meg, if I could find a place selling the 40 megger I'd be real happy! I'll pay a premium price for this drive... -- <-- David Herron; an MMDF guy <david@ms.uky.edu> <-- ska: David le casse\*' {rutgers,uunet}!ukma!david, david@UKMA.BITNET <-- <-- Controlled anarchy -- the essence of the net.
bart@amiga.UUCP (Barry A. Whitebook) (11/16/88)
In article <6055@killer.DALLAS.TX.US> aimania@killer.DALLAS.TX.US (Walter Rothe) writes: )AMAZING computing just came out with an article that shows that the 2090A )slows way down when doing a 704 by 644 by 4 bitplane overscan display. )I would expect some slowdown since this leaves only 50 slots out of a )total 226 to do all other DMA and CPU cycles during one scan line. )However, there should be plenty of time during vertical retrace to get )the needed disk activity in. Other controllers seem to be able to do this )but the 2090A does not seem to be able to use this time. What's going on? fyi: what is going on is that there is a fifo buffer between the dma controller and the scsi disk for input/output which must be serviced before over/underrun. when there is dma contention (for example 704x644x4 display) on the bus there isn't time during vblank to guarantee a full transfer of large transfers of data. so the 2090 driver is forced to transfer a block at a time and to GUARANTEE that no over/underrun occurred (you wouldnt like a single byte of your file to get corrupted, would you?) to avoid the problem when displaying a dma saturated display and transferring data with the 2090 just "drag the screen down". you'll find that the maximum transfer rate proportional to the amount of dma cycles that you free up. note that the 2090/A code is fully multitasking compatible. within this framework, the only solution to this problem is full dma/scsi handshaking via hardware control lines. bart