Understandably, this led to many existing AT ( ISA) bus cards not working properly in those systems. Although 8-bit cards could be used in 16-bit slots most of the time, there was no guarantee that they would work properly.Īs PC clone vendors began to introduce faster CPUs in their models, the AT bus ended up being clocked at anywhere from 10 to 16 MHz. This means that for example that originally the bus is as fast as the clock speed of the CPU in question: 4.77 MHz for the original PC bus and 6-8 MHz for the PC/AT. 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.īut what does it take to get started with ISA or PCI expansion cards today? The Cost of Simplicity From top to bottom: 8-bit XT bus, 16-bit AT/ISA, 32-bit EISA.Īn important thing to note about ISA and the original PC/AT bus is that it isn’t so much a generic bus as it describes devices hanging off an 8088 or 80286 addressing and data bus. 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. The name Industry Standard Architecture (ISA) bus is a retronym created by PC clone makers. 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. These slots could be used for anything from graphics cards to networking, expanded memory or custom I/O. With the IBM PC/AT these expansion slots became 16-bit courtesy of the 80286 CPU it was built around. The first IBM PC had five 8-bit expansion slots that were connected directly to the 8088 CPU. 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. 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.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |