Originally posted by: KF
Originally posted by: mosco
How Fast are ISA Slots? or should i ask how slow they are?
If I recall:
8MHz with a 16 bit bus, although there are also 8 bit ISA slots. The original IBM PC, from which what we now consider a standard PC has evolved, used 8 bit slots. Actually the 16 bit ISA was an extension of the 8 bit oriiginal that added a second connector in line with the old 8 bit connector, so 16 bit ISA can also take 8 bit cards. IBM revised its PC a couple of times, maintaining compatibility, so vendors went along with the XT and AT. The AT had a 16 bit bus. (The AT style case and mobo got revised into ATX much later.) For quite a while after everthing else converted to PCI, the usual modem card used the ISA 8 bit bus simply to implement a port which behaved like a serial interface chip. Quite a few mobos had a single ISA slot during that time (like my ABIT KT7.) Then PCI slot modems were devised that did without much of the electronics of complete modems, and PCI winmodems took over. (There were ISA winmodems before, but PCI winmodems knocked still more off the price.)
ISA = Industry Standard Architecture. This terminology came about when IBM decided to take its next bus revision private: besides not being able to fit old style cards into it, you were going to have to pay royalties to make cards that used it, if in fact IBM gave you permission. (I forget what IBM called ithe bus, but the new style computer was the PS/2.) With royalties, vendors would be at a cost disadvantage compared to IBM. So vendors organized, and devised something called the VESA local bus, which added yet another connector in line (whereupon the former bus became ISA.) There was now a line of connectors all the way from one side of the mobo to other. For a while, this was the standard advanced bus. But Intel had designed the bus of its yet-to-be Pentium CPU so that it could accomodate card slots in a simplified manner. When the Pentium appeared, motherboards using it generally had some PCI slots (really Pentium bus) rather than VESA. Despite its simplicity, PCI caught on slowly because Pentiums cost over $1000 and mobos which could use the 60MHz broiler to its capability weren't far behind. Pentium was the biggest stretch for Intel that it ever attempted (besides Itanium?) In comparison $100 100MHz AMD 486 clones bested 60MHz Pentia on the then accepted benchmarks. Eventually the Pentium line included some reasonably priced CPUs (by the standards of olden days), even AMD and the former Cyrix were making Pentium clones (the K6 and 6x86), and the cost advantage of directly using the Pentium bus (PCI) over VESA took hold.
bump
Facebook
Twitter