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- From: tweten@wilbur.nas.nasa.gov (Dave Tweten)
- Subject: Re: EISA/MCA *or* Local Bus? Which is better for multitasking?
- References: <BzBx9G.Ap@utdallas.edu> <1992Dec17.231538.29868@blkbox>
- Sender: news@nas.nasa.gov (News Administrator)
- Organization: NAS Systems Division, NASA Ames
- Date: Fri, 18 Dec 92 18:12:49 GMT
- Message-ID: <1992Dec18.181249.16793@nas.nasa.gov>
- Lines: 87
-
- In article <1992Dec17.231538.29868@blkbox> rbarnett@blkbox (Rick Barnett) writes:
- >goyal@utdallas.edu (MOHIT K GOYAL) writes:
- >>I am curious as to which is better for OS/2, EISA/MCA or VL-Bus.(Vesa Local Bus)
- >>Here is my setup:
- >>single user on a stand alone pc.
- >>I will be running lotsa programs..games, word processors, Pascal, Mathcad,
- >>whatever else.
- >>Anyways, I would like to know which would offer better performance.
- >
- >EISA is 32 bits wide with bus mastering but only runs at 8 MHz. Video and
- >hard disk controller cards are few and expensive.
-
- My experience is that EISA disk controller cards are plentiful if
- somewhat more expensive than equivalent ISA cards. Mr. Goyal says
- he's most interested in SCSI disks. The vendors of EISA SCSI
- controllers with which I was most familiar when I bought mine about
- nine months ago were Adaptec, Ultrastor and DTC. The beauty of EISA is
- if you don't want to pay the current premium on some card for EISA over
- ISA (or even PC/XT bus) you don't have to. Use an old card until the
- prices come down to your comfort zone.
-
- I should also point out that an 8.33 mHz EISA bus can transfer data at
- 33 megabytes per second in bus master mode (8.33 mHz x 4 bytes/cycle =
- 33.33 megabytes/second).
-
- >VESA is 32 bits wide with bus mastering and runs at CPU speed (up to 50 MHz).
-
- I don't think this is exactly true. My understanding is that the VESA
- specification requires VL boards to work up to 33 mHz, not 50. It's
- also important to note that the standard works only for three slots.
-
- >>Also, does it even matter? (ie-if EISA/MCA is much better, will it matter?
- >>will I ever make full use of Local Bus, or vice versa?)
-
- The function which will most benefit from a VL board is video
- (remarkable, considering that VESA is a video standards group!). EISA
- gets most of its speed through parallel transfer and reduction in the
- number of bus cycles per transfer after initial set-up. Much video
- work amounts to byte shuffling. The VL bus's faster cycle time works
- wonders when you just need to move one byte per transfer. By contrast,
- EISA shines when you need to move blocks of data to/from several I/O
- boards (say, an ethernet, a single-ended SCSI, a differential SCSI and
- an ESDI).
-
- >>I plan on having a scsi-2 hard drive and a scsi cd rom.
- >
- >I have seen specs on two VL-Bus SCSI controllers, with data transfer rates
- >up to 66 MBytes per second - since SCSI-2 maximum is 10 MB/sec, you can hang
- >a few drives on it without saturating the I/O channel.
-
- Any non-wide SCSI-II controller is limited by the SCSI spec. to 10
- megabyte per second transfers over any reasonable amount of time. A bus
- mastering EISA SCSI controller will chop that 10 mB/s stream into 33
- mB/s bursts. A caching controller can deliver data already in the
- cache at burst speed, which is probably where Mr. Barnett's number comes
- from.
-
- Mr. Barnett is right when he says, "you can hang a few drives on it
- without saturating the I/O channel," if he means the SCSI bus. If you
- get a true Fast SCSI-II disk, it will burst its data across the SCSI
- bus at 10 mB/s, even though the data rate at the disk heads is more
- like 3-5 mB/s. That permits one SCSI bus to support two or three
- solidly busy disks. Be careful, though. Most advertized SCSI disks
- aren't Fast SCSI-II. A slower disk can drag the SCSI bus down to 1.5
- mB/s while it deals with that disk.
-
- Neither Mr. Barnett nor I have mentioned MCA bus to this point. I
- wouldn't consider it. IBM made a big mistake by initially charging
- relatively large royalties for its use. The result was EISA. The
- market has passed MCA by. Low volume means few choices and a
- continuing premium for MCA cards.
-
- For what it's worth, my ideal motherboard would run at 33 mHz and have
- EISA slots with one of them additionally capable of supporting VL
- bus (for my video card, naturally). If I had just won the lottery, the
- CPU chip would be a 486DX2-66, otherwise a 486DX-33. Such boards are
- currently available.
-
- >Hope this helps...
- >Blair R. Barnett u5c95@lfhp113.hso.link.com
-
- And so do I.
- --
- ---------------------------------------------------------------------------
- Dave Tweten tweten@nas.nasa.gov
- NASA Ames Research Center, M/S 258-5 (415) 604-4416
- Moffett Field, CA 94035-1000 FAX: (415) 604-4377
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