How To Recognise Computer Expansion Cards

People sometimes marvel at my ability to recognise a particular type of computer add-on card and tell them what kind of computer it was designed to plug into. This page is an attempt to show a few examples, to help others to spot classic computer parts amongst the dross.

Introduction

Here's an example of a classic computer board, compared to two modern PC add-on cards. The big card is a disk controller from that most classic of computers, the PDP-11; the card at top left is a network card for a 16-bit ISA bus slot, and the card at top right is a PCI sound card. The 10 megabit Ethernet cards are being thrown out by IT departments all over the place. PCI sound cards are available at computer fairs for a few pounds. PDP-11 boards are irreplaceable examples of late 1970s technology, and should be conserved with great care.

Now let's compare memory boards. The large board here is a 32k byte memory board for a PDP-11; the smaller board is a 256M byte DIMM for a modern PC. Note the metal stiffener (at the bottom of the photo) and the lock and eject levers on the much more substantial PDP-11 board. The DIMM standard places the lock and eject levers on the PC motherboard, and has no need of metal stiffeners. The PDP-11 board holds 32768 bytes, while the DIMM holds 268435456 bytes, a factor of 8192 bigger.

The Eight-Bit Generation

Here's a rare one. This is the board inside the 16k byte expansion module for the Jupiter Ace. The Jupiter Ace was a spin-off from the Sinclair ZX81 and ZX Spectrum, but instead of using a BASIC interpreter, it had a FORTH language system. Not many were sold. Note the eight 4116 DRAM chips, in 16-pin DIL packages. The chips have date codes “8232”, which means they were made in the 32nd week of 1982.

This memory board was produced by Watford Electronics in the early 1980s. It was designed to be used with an expansion motherboard that could be connected to several machines of that era. I bought one and hard-wired it to my Compukit UK101. It holds 8k bytes (8192 bytes) of memory, in 16 2114 static RAM chips. Once again, the RAM chips are in DIL packages (18 pin) and in this case are in sockets.

Coming soon: Apple ][ and Apple /// expansion boards, BBC Micro upgrades and Sinclair RAM packs.

The Acorn Archimedes

This expansion board is a video add-on Podule for an Acorn Archimedes. Note the DIN 41612 connector on the right-hand side, and the Acorn mounting bracket on the left.

The IBM-Compatible PC

Although this board looks like a normal IBM PC expansion card (ISA bus), it's not. It's actually an AST Fastram board, designed for use in special RAM slots in AST 286 motherboards. Note the additional gold-plated edge connector on the bottom left-hand side of the board. The RAM chips are 256k by 1-bit DRAMs, so the total capacity is a staggering 2Mbytes. Only the first 512kbytes are soldered in; the rest are in sockets and have been added as upgrades.

DEC TurboChannel boards

Two boards from DEC that can be used with either the MIPS-based DEC 5000 or the DEC 3000 with an Alpha processor.

Sun SBus boards

First, a Sun SPARC CPU board, which is actually an MBus card. Note the heatsink on top of the CPU chip and the power regulator module on the right-hand end of the board.

Networking Devices

It's sometimes important to recognise when a board is not a computer expansion card at all, but an add-on to something else. This is a two-line ISDN interface for a small router. On the underside, it has a DIN 41612 connector, a sure sign that this is no PC add-on card. The two small daughter boards (or should that be grand-daughter) plug in to the main board. All the major chips are embedded-systems versions of the 68000.