First post, by TheMobRules
The pre-VLB/PCI 486 era is of great interest to me, in particular the attempts of several manufacturers to overcome ISA bus limitations by introducing their own proprietary local bus implementations, none of which seems to have been successful as shortly after VLB became the de-facto standard until PCI took over for good.
My goal with this thread is to focus in the local bus implemented by ECS in a couple of their motherboards, benchmark its graphics performance when using an ECS Local Bus (ELB) video card vs. an ISA card with the same chipset from that era and determine how much of an advantage it would have in that short period before VLB became commonplace. I will be conducting the tests using an Intel 486DX-50, which was the "ultimate" Intel x86 CPU at the time, at least until the DX2-66 was introduced (Aug-10 1992 according to CPU World).
*** Motherboard ***
I found this ECS SL-486E board on eBay for a very reasonable price on eBay when looking for EISA stuff:
Initially, I thought is was VLB and it was listed as such (for obvious reasons, just look at the bottom slot), but after some quick research I learned that it is actually the proprietary ECS local bus. So, I hesitated to buy it since the seller listed it as "working and tested with a VLB card", knowing that inserting a VLB card would either just not work (best case scenario) or produce some magic smoke, maybe blowing some components out. Also, even if it did work, it would be almost impossible to find an ELB graphics card, without which it would be really uninteresting.
However, while browsing other items listed by the seller I found what was listed as a "VLB graphics card" with the Tseng ET4000AX chipset and suddenly it clicked! A quick search on TH99 revealed that this was one of the two known ELB graphics cards (the other one having an S3 911 chipset), so it was most likely pulled from the same system as the board and it is what the seller probably used to test the board thinking it was VLB. So I pulled the plug and bought both!
*** Graphics Card ***
The label on the BIOS chip seems to identify the card as a VI-811/833. It looks just like a standard VGA card with the ET4000AX chip, 1MB of 70ns DRAM, AT&T DAC, clock generator and a few PALs and logic chips:
When I got the board and graphics card, I did some quick tests, modified the Dallas DS1387 chip to use a coin cell battery and everything seemed to work just fine. But suddenly I started to get artifacts on the screen, which made me very sad due to the relative rarity of these components. Luckily, the great VOGONS community came to the rescue and the amazing troubleshooting skills of mkarcher allowed me to identify and fix the broken inner trace on the motherboard that was causing the artifacts. See this thread for more details and an almost complete pinout of the ECS local bus!
By digging into the graphics card BIOS I found that it identifies as a Genoa MultimediaVGA 7900 series. There is some info online about the ISA version of the same card, but nothing about the ELB variant. However, the drivers I found detect the card and work perfectly, both on Windows 3.1 and the VESA 1.2 TSR (which is very useful since the BIOS is VGA only, no support for VESA modes built-in and UNIVBE does not work properly). The card can do 16M color, which Genoa proudly touts in the setup program, to the point of including a DOS app to demo that capability. I am attaching both the BIOS and drivers to this thread in case it's useful to someone else:
*** Test setup ***
This is the setup I will be using for the tests:
- CPU: Intel 486DX-50
- Motherboard: ECS SL-486E
- Cache: 256KB 20ns SRAM
- RAM: 8MB 70ns FPM
- Graphics card: VI-811/833 ET4000AX 1MB (ECS local bus)
- Controller: BusTek BT-742A EISA SCSI Host Adapter
- HDD: IBM 449MB SCSI HDD
- FDD: 3.5'' 1.44MB floppy drive
Considering the bus is running at 50MHz, the following are the tightest timings I was able to achieve in the BIOS for the system to be stable, otherwise it wouldn't get past the POST (I also had to set JP3 on the graphics card to run at 50MHz, which probably introduces a wait state):
NOTE 1: switching to 15ns cache chips didn't allow me to tighten the timings any further so I left the 20ns ones that came with the board. Similarly, for the RAM I left the original 8MB 70ns as I couldn't use better timings even with 60ns SIMMs.
NOTE 2: regarding the RAM, the board seems to do some kind of interleaving as filling a single bank I get a Memory Bandwidth of around 85 MB/s in SPEEDSYS, while both banks filled get me to 114 MB/s. There doesn't seem to be any other noticeable performance increase though.
The following post will include results of running various tests from Phil's DOS Benchmark Pack, and comparing them to an equivalent ISA card with the same ET4000 chipset.