DCS 286 Motherboard Review - Part 3
In parts 1 and 2, we got the DCS 286 motherboard up and running, dug around the BIOS a bit, and got it to boot to a fresh hard disk (low-capacity CF card). Now onto some benchmarking... I'm sure I can get this thing running faster!
Benchmarking
As I learned from the 386 motherboard with C&T chipset, there are a number of tweaks you can make to speed up the performance of this motherboard.
The synthetic benchmarking tools I will be using consist of:
- MaxSpeed
- Landmark Speed Test v0.99
- Landmark Speed Test 6.00
- Norton SI (SysInfo) v4.5
- Norton SI v8
To get a baseline set of performance figures, the system gets the following synthetic benchmark timings:
| Turbo On (open) | Turbo Off (short) | |
| MaxSpeed | 12 MHz | 6 MHz |
| Landmark Speed Test v0.99 | 15.9 to 16.1 (9.8x to 10.0x) | 7.8 (4.6x) |
| Landmark Speed Test v6.00 | 18.26 MHz (CPU clock reports as 12.027 MHz) | 9.01 MHz (CPU clock reports as 6.003 MHz) |
| Norton SI v4.5 | 13.7 | 6.7 |
| Norton SI v8 | 9.1 | 4.4 |
This is with the out of the box default BIOS settings which are:-
- 1 wait state on memory
- Processor clock set to CLK2IN
- Bus clock set to CLK2IN/2
- DMA clock set to SCLK/2
- BIOS Shadow disabled
- Memory Page Interleave disabled
A Word About Clocks
Several crystal oscillators exist on these 286 motherboards - they are used by the system as the source of several 'clocks'. The crystals are used by a clock generator chip which takes the crystal frequency and uses it to control the timing of the most important parts of the computer. On motherboards with chipsets, this clock generator is usually built into one of the chipset chips.
CLKIN is the System Clock. This controls the frequency in MHz the CPU is driven at. On 286 and 386 machines, this is half the speed of the main crystal - the CPU divides it by two, hence it's often called CLK2IN. Since this DCS motherboard came with an 80286 running at 10 MHz, we have a 20 MHz crystal.
Incidentally, 486-class motherboards run the CPU at the same frequency as the System Clock - they can do this because they use both edges of the timing signal, which is a square wave.
ATCLK is another clock signal that comes from the clock generator - this one is used by the bus if it's run asynchronously (decoupled from the CPU's speed), otherwise the bus will use the above CLKIN (the System Clock) just like the CPU, except it would use a different divider, e.g. if the CPU were 33 MHz it would use CLKIN/2 for the CPU but use CLKIN/4 for its ISA bus to give it the standard 8 MHz.
On later motherboards that support PCI, this is referred to as PCICLK - the ISA bus speed is then controlled by the PCICLK, e.g. PCICLK/4 if it's a 33 MHz PCI bus.
ATCLK is also used to control the speed of memory access. Depending on the rated speed of your memory chips, you may or may not need wait states (basically delay signals) to be added to slow down the demands being made on the memory chip.
DMA controllers allow certain peripherals to access memory directly. In some BIOSes you can select the "DMA Clock Source", like I can with this chipset. Usually this runs at half the bus speed, i.e. ATCLK/2 or SYSCLK/2. The maximum is usually 5 MHz.
A lot of boards also have a 14.31818 MHz crystal oscillator - this is a throwback from XT days where it would be used for all system timing. On later motherboards it's used to control the colour frequency of the video controller (6845 CRT controller chip), though some chipsets like the BX still use it for some system timing.
Sadly, there is a pretty bad bug in this BIOS. It seems I cannot retain the Basic Setup details and then alter any characteristics in the Extended Setup - any changes made in Extended Setup reset the Basic Setup back to their defaults, and vice versa. Since I need to retain the hard disk and floppy drive configuration, this prevents me from tweaking other aspects of the BIOS to improve performance, which is a shame.
The motherboard does have some DIP switches though, which impact performance, as follows:
| SW1 - CPU Half Speed | MaxSpeed = 6 MHz So this switch does the same as when the turbo switch is on (meaning turbo off). Toggling the turbo button when this switch in ON does not halve the speed again. |
| SW2 - I/O Half Speed |
MaxSpeed = 11 MHz - 12 MHz |
| SW3 - RSEL0 | Setting this to ON caused a "CMOS Memory Size mismatch" message when I rebooted. New memory reported was 640 KB only, so this switch possibly disables extended memory. |
| SW4 - RSEL1 | Setting this to ON caused a "CMOS Memory Size mismatch" message as well on reboot. New memory reported from the BIOS was 512 KB only. Setting both SW3 and SW4 to ON caused the same memory size mismatch message to appear, and the BIOS reported total memory to be 256 KB. |
So setting SW2 to ON decreased performance slightly; it may be present to support slow ISA expansion cards that cannot cope with faster speeds.
SW3 and SW4 appear to work in tandem and define the memory installed, with the following settings:
ON, ON = 256 KB
OFF, ON = 512 KB
ON, OFF = 640 KB
OFF, OFF = 1024 MB
REAL-WORLD TESTING
More to follow....