Depending on whether you feel happy soldering surface mounted components you may want to go for a ready made and tested board or start with a partly assembled kit to finish yourself.
However the original article hinted that you can eliminate 3 chips by replacing the read buffer and write latches (74LS373 and 74LS241) with read back latches, in particular the 74ALS990 is suitable.
By choosing surface mounted components instead of through hole DIL parts the board size can be further reduced to just 3" by 3.5" which includes a full megabyte of RAM. The filing system supports up to 8 megabytes and a fully decoded address signal is available on a 21 way header should you need it.
Optional terminating resistors may be fitted if there are no other devices plugged into the 1MHz bus, or these can be omitted and the integral loop through connector used to "daisy chain" the other 1MHz bus devices together.
A 1.3mm power plug supplies the board with +5V.
Two 32 pin sockets house either 1x4Mbit, 1x1Mbit, 2x4Mbit or 2x1Mbit chips depending on how much RAM is needed in your case. Current consumption is 125mA quiescent, rising to around 130mA average during RAM accesses.
When assembled the result is a high speed high capacity solid state RAM disc:
The RAM disc boards are available now, and are offered in various different options depending on how confident you are at soldering. For most users, the 256kB RAM option matches the normal 200kB DFS floppy disc close enough:
| Option: | Price: | Comments: | ||||||
| The custom PCB plus the 74ALS990 latches |
| Incase you find the latches hard to find You source the remaining components (Digikey/Farnell/etc...) You build the board as per the article and layout Does not include RAM chips (see later) | ||||||
| Buy the finished board |
| The option if you're not happy soldering or working with surface mount Receive a built and tested board Includes approx 60cm of ribbon cable to the 1MHz bus port Plug it in and away you go Does not include RAM chips (see later) | ||||||
| RAMFS on EPROM |
| Latest version of RAMFS programmed into ROM |
| Option: | Price: | Comments: | ||
| 128k byte |
| Only when bought at the same time Links need altering from '4' to '1' position | ||
| 256k byte |
| Only when bought at the same time Links need altering from '4' to '1' position | ||
| 512k byte |
| Only when bought at the same time Leave links in '4' position | ||
| 1M byte |
| Only when bought at the same time Leave links in '4' position |
