Motherboards

When is 50MHz Faster than 66MHz?
EISA vs VESA or EISA/VESA & Vice Versa
An Apt Description
16-Bit Satisfaction
Upgrading Your 8088

When is 50MHz Faster than 66MHz?
From Catalog 36, page 58

Sounds like a riddle, doesn't it?

It isn't a riddle, but the question would make more sense if I elaborated. Perhaps the question should read, "When is a 486DX-50 faster than a 486DX2-66?"

A 486DX-50 runs at 50 megahertz for all operations all of the time. The 486DX2-66 uses a 33 megahertz clock that is doubled for internal processing, but all external activity such as I/O transfers and main memory requests are executed using the 33 megahertz source.

A clock doubled to 66MHz is usually benchmarked at 1.7 times the throughput of a 33MHz processor. The 0.3 that is wasted is the time the computer spends working at 33MHz on the external operations.

So the conclusion is that if your machine frequently works with fresh data that isn't in the processor cache, a 50MHz machine might achieve better throughput than a clock doubled 66MHz computer, and even if it isn't faster, it could deliver more bang for the buck.

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EISA vs VESA or EISA/VESA & Vice Versa
From Catalog 36, page 15

If you are contemplating a motherboard purchase, you may very well be debating questions like the one above. In many areas, EISA and VESA local bus support are very similar, and choosing between them is strictly a cost issue. However, there are strengths in each that may sway your purchase one way or the other. You may even decide you want both!

EISA strengths include robust support for reusable interrupts, reassignable port addresses and vendor card selections that stress fast and wide I/O operations.

VESA advantages are an inexpensive interface, very fast memory transfers, and superior vendor support for video cards.

Both provide support for the ISA cards you may already have, including 8 and 16-bit interfaces from 8088's and up.

So, you may ask, who would choose EISA and VESA on the same motherboard? Anyone who wants workstation performance, and most server applications, are candidates for a dual board.

I would optimize my PC by choosing VESA video and cached IDE along with EISA LAN support. My FAX/Modem would be ISA as would the mouse, because serial transfers aren't data bound. Another example of the title being more fun than the article that follows. My only regret here was that it couldn't also be a tongue twister.

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An Apt Description
From Catalog 27, page 7

EISA (Extended Industry Standard Architecture) might actually be an intended pun because it describes both the electronic nature of the extension and the physical nature of the card connector extension at the same time.

The original IBM PC-AT bus had two edge connectors between the daughter cards and the motherboard, providing a 16-bit data bus and addressability for up to 16 megabytes of memory. With the advent of the 80386 and its 32-bit bus, manufacturers began looking for a way to "extend" the bus to handle the additional throughput requirements.

IBM created the Micro Channel, while other vendors sought a more compatible approach. EISA fully supports the two ISA bus connectors above the longer EISA slots. Cards designed for use in AT-compatibles will plug and play in EISA machines, but not vice versa.

Considering an EISA motherboard? Then also consider (in this order): an EISA drive controller, video controller, and networking card if applicable. Cards like serial, parallel, mouse and game controllers gain no advantage by being EISA specific.

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16-Bit Satisfaction
From Catalog 26, page 8

The popular press would have you believe that DOS, 8088s and 80286's are passe. If you buy into the Windows and OS/2 views of the world, nothing less than a 386SX will satisfy.

If you want every business letter to be a work of art, then you need desktop publishing software and a powerful computer to run it on. On the other hand, if you want economical production, and easy training, a good word processor on even the slowest 8088-based computer is faster than it needs to be.

For dedicated tasks, and even process control, an 8088 base is usually just fine. Consider an 80286 if you need high density disk support. And if you want to run OS/2, which is my choice for a 32-bit system, then you need at least an 80386.

I regret that I wrote this. Even though it wasn't so long ago, I think I was providing justification for people who were afraid to learn a new interface. The difference between a "simple" letter written with a text editor under DOS versus the same letter written with a word processor in Windows is as striking as hand printed versus typed.

While 8088 and 80286 PC's still have their uses, pretending that they can do as much, or as well in mainstream applications is self delusion. I still use an 8088, but it is confined to receiving faxes and serving as a test bed for product development (if I blow it up, who cares?).

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Upgrading Your 8088
From Catalog 9, page 8

Upgrading your 8088 is easy, and will never get much less expensive! If you've been thinking about replacing your 8088 motherboard with a 286 motherboard, now's the optimum time! The price for a 286 motherboard has gone about as low as it'll ever get. The technology may marginally improve in the next year or so, but not by much. Your initial investment in high speed computing need be no more than the cost of the motherboard itself. That's it!

If you have at least 512K of memory (using 41256 chips), then all your current peripherals (with the possible exception of serial ports and keyboard*) will be usable on a replacement motherboard. This includes your case, power supply, display, floppy drives and hard disk drives. To use your current memory, you may have to run at a slower clock setting, but even then you'll get 4-5 times your current throughput.

Board replacement is easy. Begin by unplugging the power connector and all of the peripheral cables. Open the case and remove the cards from their slots (you can probably leave the cables to the disk drives connected throughout the replacement). Finally, remove the screws holding the motherboard in place and slide the board out. Reverse this procedure to install the new board. **

Later, if you decide to enhance its performance, you can replace some of the peripherals with their faster 286 counterparts. For the greatest effect on throughput, consider a 1:1 interleave 286 floppy/hard disk controller, more and/or faster memory, and a 16-bit display card.

* Note: Original PC keyboards without the ability to switch into AT mode will require replacement, and some serial ports may not keep up at faster speed settings.

** Note: Some very old cases may require minor modifications to accommodate the additional 1 inch of board length.

Back when this column was relevant, I frequently gave the advice it documents. I wish I could spend the space required to explain why the keyboard or serial port might not work since I found it interesting. (Others point out that most people aren't interested in building a clock, they only want to know the time.)

Be that as it may, the situation today is much, very much, easier. If you have a 286 or greater, just replace the motherboard, and memory if necessary, with the new faster motherboard of your choice. Your old keyboard, serial ports, and even the case should not present any problems whatever.

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