You Got Something On Your Processor Bus: The Joys Of Hacking ISA And PCI

Although the ability to expand a home computer with more RAM, storage and other features has been around for as long as home computers exist, it wasn’t until the IBM PC that the concept of a fully open and modular computer system became mainstream. Instead of being limited to a system configuration provided by the manufacturer and a few add-ons that really didn’t integrate well, the concept of expansion cards opened up whole industries as well as a big hobbyist market.

The first IBM PC had five 8-bit expansion slots that were connected directly to the 8088 CPU. With the IBM PC/AT these expansion slots became 16-bit courtesy of the 80286 CPU it was built around. These slots  could be used for anything from graphics cards to networking, expanded memory or custom I/O. Though there was no distinct original name for this card edge interface, around the PC/AT era it got referred to as PC bus, as well as AT bus. The name Industry Standard Architecture (ISA) bus is a retronym created by PC clone makers.

With such openness came the ability to relatively easy and cheaply make your own cards for the ISA bus, and the subsequent and equally open PCI bus. To this day this openness allows for a vibrant ecosystem, whether one wishes to build a custom ISA or PCI soundcard, or add USB support to a 1981 IBM PC system.

But what does it take to get started with ISA or PCI expansion cards today? Continue reading “You Got Something On Your Processor Bus: The Joys Of Hacking ISA And PCI”

A Retrocomputer Disk On A Chip

There have been a lot of different mass storage methods over the relatively short lifespan of the computer. Magnetic tapes, drums, all sorts of disks, and flash memory have each had their time. Each of these new innovations required some time to become easy to use. One of the early attempts to simplify using flash memory was the M-Systems DiskOnChip device. Looking like a standard 8K JEDEC-compatible memory device, it actually provided access to a flash disk drive ranging from 16MB to 1GB. [Smbakeryt] bought some of these devices and built an ISA board to provide a disk and clock for the old 8-bit bus. You can see a video discussion about the device below.

SanDisk bought M-Systems and discontinued the devices back in 2007. Of course, you can still design flash memory into your system, but the simple and efficient interface of the DiskOnChip is no more. It is a testament to how simple the interface is that the schematic for the little board fits on a page, including the DS12885 real time clock.

Continue reading “A Retrocomputer Disk On A Chip”