Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.csd.uwm.edu!cs.utexas.edu!uunet!portal!cup.portal.com!cliffhanger
From: cliffhanger@cup.portal.com (Cliff C Heyer)
Newsgroups: comp.arch
Subject: Re: SRAM vs. DRAM, 33MHz 386 UNIX-PC
Message-ID: <22011@cup.portal.com>
Date: 9 Sep 89 19:09:46 GMT
References: <21936@cup.portal.com> <46500076@uxe.cso.uiuc.edu>
Organization: The Portal System (TM)
Lines: 51


>I think SRAMS somewhere on the order of 5x the cost for the same amount
>of memory, and they also take up at least twice the board space.  

Got some recent prices:

#1) SRAM 
#     4--64K (70--100ns)   $4
#     4--64K (25--55ns)    $10
#     256K (70--100ns)    $15
#     256K (25--35ns)     $30
#     1Mbit    $100
#
#2) DRAM 
#     256K     $4
#     1Mbit    $12
#     4Mbit    $100

For 1MB, looks like about an extra $300 to $1200 for the chips. BUT what about
the cost to engineer new boards for the high speed chips? $50,000 workstation
prices....+ extra power...

>> 4. Are any board makers making (or have made) motherboards with ESDI and/or
>> SCSI interfaces ON BOARD to bypass the 8MHz AT bus? 
>Even that's not enough.  SCSI, for example, is still only 8 bits wide, and it's
>maximum transfer rate of 4 megs/second is in the same ballpark as the fastest
>AT buses.  This is what Amiga hard disk controllers do (DMA), and we get up to 900k/sec
>through the filesystem using asynchronous SCSI (1.5 megs/sec). 

Sounds like Commodore is really *trying* to put out a "best" product...I wonder
about many others. For example, IBM PS/2s always score the lowest in disk I/O. I
assume this is because they want to *encourage* customers to shift the needed
I/O BW to IBM big iron.

What about SYNCHRONOUS SCSI in the Amiga? (4.0MB/sec) Or DMA & memory 
can't handle it at this speed(?)

Do sync & async are about the same cost? Why use synchronous SCSI vs. 
async? 

Actually I must admit I don't know that much about the AT bus. 
What is the AT bus rated at in aggregate and effective MB/sec throughput?

 (For example, I assume it is
16 bits wide? Does this mean at 8 MHz it's aggregate throughput is 16MB/sec?
But I suppose because of DOS I/O is done via 8 bit bytes...which would give
8MB/sec. Still this sounds awfully high - A 15MHz ESDI drive transfers at
15Mbits/sec which is 1.5MB/sec, but this is said to be too fast for 
the AT bus.....and so the 10MHz ESDI  is used.)

Cliff