80-Bus News

Plugging It In

That is almost all you have to do! The board includes one mini-DIP switch, (4 pole), and two links.

The mini-DIP switch is used to select the board number in a multi-RAM-DISK-board system and, in most cases, will not need changing from its setting of 0, (Unless Gemini change their test procedures and they come set to some other value!).

LK1 will provide you with a NASIO signal if your system requires it, but most people will not need it, or will have another board in the system supplying it already.

LK2 allows the clock input to the board to come from either the CLK line, or the AUX CLK line. If you do not have a 4MHz system clock, you will have to cut the trace between 1 and 2 on LK2, and connect 1 to 3 in order to pick up 4MHz from the AUX CLK line. (Assuming it has been implemented on your system).

Soft­ware Support

Gemini BIOSs Versions 2.3 and higher support GM833. Also the associated program CONFIG has been extended to include the board as an option when setting up the parameters for a “Memory drive”. If you have an earlier BIOS, a BIOS update program (together with CONFIG) should be available through your usual dealer.

The BIOS supports the drive as drive “M”, and is so arranged that it does not re-initialise the memory drive if you are forced to press Reset.

SIZE

The standard board provides a memory drive of 512k (or 0.5Mbyte) capacity – quite a respectable size. However if this is not enough for you further boards may be added up to a maximum of 16, so providing the full 8Mbyte capacity that CP/M2.2 will support. (N.B. 16 boards are beyond the capacity of the currently available commercial 80-BUS backplanes, and may also require added power supply capacity!).

I find the 512k single-board drive more than adequate. It lets me keep a reasonable amount a system software on the drive (such as Wordstar Overlay files) along with all the data files. You may like more if you are handling particularly large data bases.

GM833 in use – Benchmarks

To give an example of the benefits of GM833 a few Benchmarks are shown below. So that a reasonable assesment can be made of relative performance I have also included figures for 5.25″ and 8″ floppy-disk drives, and the Gemini Winchester disk subsystem. As always the figures should be taken as a guide only, as the figures for the floppy disk performance can be made to vary widely, depending upon where the files are located on the disk. I have attempted to position the files in such a way as to produce ‘average’ figures.

The first benchmark is an example of how a program can be transformed by the use of RAM-DISK. The program in question is Translat, a program that translates 8080 mnemonics to Z80 mnemonics. Who ever wrote the program made no attempt to optimise the IO – the internal input and output buffers appear to be one sector in size. The result is that the majority of the run time of the program is taken up by the disk drive moving the head back and forth between the tracks holding the input and output files. The RAM-DISK has no such physical problem!

(N.B. another such program nearly gave me a heart attack when I used it to compare files on two different drives. It briefly turned my system into an imitation of a machine gun as the heads on the two 8″ drives alternately loaded and unloaded several times a second.)

Anyway here are the figures for Translat working on a large 8080 source file. The number in brackets is the approximate number of tracks that separated the source and destination files.