Text File

Aucbvax.2440 fa.works utzoo!decvax!ucbvax!works Sat Jul 25 16:04:49 1981 Collected responses on global configurations >From WorkS-REQUEST@MIT-AI Sat Jul 25 15:57:50 1981 ------------------------------

Date: 24 Jul 1981 15:41 PDT From: Deutsch at PARC-MAXC Subject: Re: More on configuration In-reply-to: BHYDE's message of 23 Jul 1981 1116-EDT To: WorkS at MIT-AI

There is no "huge increase in cost of communications that local networks imply versus front ends". The multiplexing cost is the very large hardware (protection, etc.) and software overhead required for time-sharing a mainframe. Ethernet-style local networks have lots of bandwidth and are extremely cheap. The bandwidth is needed to make reasonably fast access to shared (either read-only or read-write) information feasible. If you time-share a mainframe, the bottleneck becomes the processor instead, and it's a lot more expensive to speed up the processor than the communications network.

The cost of processor power is very misleading. If you are talking about the power available to run a single thread (job), then indeed there are great economies of scale. However, if you want to run N jobs, the overheads of multiplexing processor and memory, and the extra I/O required to get those jobs in and out of the fast, expensive mainframe (which also goes up linearly with N), may kill you. Proper planning for a computing facility must make some judgments about the mix of computation-intensive jobs, for which a fast, expensive, shared mainframe is necessary, against the interaction-intensive jobs, for which workstations win out. Similar comments apply to disks, printers, and long-distance communications: whenever there is an economy of scale, you have to decide how much of what capacity device you want. The one thing where centralization produces DISeconomies of scale is interaction bandwidth. That's what the increasingly cheap workstation tech- nology is buying us.

------------------------------

Date: 24-Jul-81 11:38:50 PDT (Friday) From: Hamilton.ES at PARC-MAXC Subject: Re: More on configuration

Based on two years of living on an Ethernet, I maintain that any network that does not give every user an effective data rate of at least 56KBits/sec is of very limited usefulness. Even with 24 MBytes of local disk, we do a lot of file transfers -- swapping files in and out if we're tight on space, retrieving new documents and software, fetching obscure symbols files to track down bugs, etc. You can get away with 9.6 KB phone lines for fetching/storing on an overnight/ archival basis, but for real-time interaction, I regard 56KB as the minimum acceptable.

The point about individual workstations being more cost-effective has at least two major aspects: (1) Operating systems can be more efficient when they don't have to worry about "fair" allocation schemes and elaborate protection mechanisms. (2) System-wide reliability is \far/ higher -- you never have hundreds of people sitting around with the computer down, unless you have a massive power outage. At worst, if the network goes down, people have to wait a while to do printing or backup.

I've always thought Grosch's law, about computing power going up as the square of the price, was a myth -- it's really more like the square root of the price, when you consider the value of redundant machines. Does anyone really believe that one $6M 3033 system is worth more than 100 $60K PDP-11/24 systems? There's also the phenomenon that software vendors tend to charge in proportion to the cost of the hardware that their system is to run on. The firstcopy of the same package might cost $500 for a CP/M version, $5K for an RSX-11M version, and $50K for an MVS version.

--Bruce

------------------------------

Date: 25 July 1981 0946-EDT (Saturday) From: Hank Walker at CMU-10A (C410DW60) Subject: workstations vs big CPU

In general, the price/performance of a CPU is no longer a function of scale (I am ignoring packaging). The rate of improvement of fast expensive technology, such as ECL gate arrays, is no greater, or even less than that of VLSI NMOS/CMOS technology. In other words, the power per dollar is going up at the same rate in each of these two price ranges. The point of communication costs can be argued both ways. Ethernet costs something like $2/foot, plus the transceiver cost of several hundred dollars today, soon to come down. This seems more expensive than RS232 into DZ11's. On the other hand, CMU is going away from its centralized front end to terminal concentrators on the Ethernet. This is due to the cost of stringing wires, and the difficulty in getting more performance out of a centralized unit.

------------------------------

Date: 24 Jul 1981 1142-PDT From: Michael Dolbec <CSD.DOLBEC AT SU-SCORE> Subject: Re: More on configuration To: BHYDE at BBNG In-Reply-To: Your message of 23-Jul-81 0816-PDT

On the leverage of buying large systems:

I think you are essentially correct about leverage available in buying a large system as opposed to many smaller personal workstations but you miss another point. The problem is that technology keeps blazing even after you buy your cost-effective large system. You stay current for a small time and then you start to fall behind current hardware and since the chunk of money necessary to purchase your large system is substantial you can't just go out and buy another right away. You must wait a relatively long time before you can purchase your next state-of-the-art mainframe [son of VAX or whatever].

Thus, your fast expensive technology rapidly gets outdated and since you can't replace it immediately your fitting the concave upward technology curve with a large step function (you buy a large system and you touch the curve, as time progresses the curve arcs up but you cannot afford to buy a new machine so your curve goes horizontal, finally you buy a new machine and touch the technolgy curve again).

If you choose the personal computer route you can fit the technology curve much closer, with a much smaller step function. The function represents the relatively small incremental cost of buying new personal workstations every so often in order to keep pace with the latest technology.

--Mike

------------------------------

End of collected responses on global configurations ***************************************************

----------------------------------------------------------------- gopher://quux.org/ conversion by John Goerzen <jgoerzen@complete.org> of http://communication.ucsd.edu/A-News/

This Usenet Oldnews Archive article may be copied and distributed freely, provided:

1. There is no money collected for the text(s) of the articles.

2. The following notice remains appended to each copy:

The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996 Bruce Jones, Henry Spencer, David Wiseman.