Processor Direct Slot or
PDS, was a solution (actually, a whole number of different solutions) introduced by
Apple ComputerApple Inc. is an American multinational corporation that designs and manufactures consumer electronics and computer software products. The company's best-known hardware products include Macintosh computers, the iPod and the iPhone...
, in several of their Macintosh models, to providing a limited measure of hardware expandibility, without going to the expense (in both desktop space and selling price) of providing full-fledged
busIn computer architecture, a bus is a subsystem that transfers data between computer components inside a computer or between computers.Early computer buses were literally parallel electrical buses with multiple connections, but the term is now used for any physical arrangement that provides the...
expansion slots.
Typically, a machine would feature multiple bus expansions slots, if any.
Processor Direct Slot or
PDS, was a solution (actually, a whole number of different solutions) introduced by
Apple ComputerApple Inc. is an American multinational corporation that designs and manufactures consumer electronics and computer software products. The company's best-known hardware products include Macintosh computers, the iPod and the iPhone...
, in several of their Macintosh models, to providing a limited measure of hardware expandibility, without going to the expense (in both desktop space and selling price) of providing full-fledged
busIn computer architecture, a bus is a subsystem that transfers data between computer components inside a computer or between computers.Early computer buses were literally parallel electrical buses with multiple connections, but the term is now used for any physical arrangement that provides the...
expansion slots.
Typically, a machine would feature multiple bus expansions slots, if any. However, there was never more than one PDS slot. Rather than providing a sophisticated communication protocol with
arbitration between different bits of hardware that might be trying to use the communication channel at the same time, the PDS slot, for the most part, just gave direct access to signal pins on the CPU.
Thus, PDS slots tended to be CPU-specific, and a card designed for the PDS slot in the
Motorola 68030The Motorola 68030 is a 32-bit microprocessor in Motorola's 68000 family. Released in 1987, the 68030 was the successor to the Motorola 68020, and was followed by the Motorola 68040. In keeping with general Motorola naming, this CPU is often referred to as the 030 .The 68030 features an on-chip...
-based Macintosh SE/30 would not work in the
Motorola 68040The Motorola 68040 is a microprocessor from Motorola, released in 1990. It is the successor to the 68030 and is followed by the 68060 In keeping with general Motorola naming, the 68040 is often referred to as simply the 040...
-based Quadra 700.
The one notable exception to this was the PDS design for the original
Motorola 68020The Motorola 68020 is a 32-bit microprocessor from Motorola, released in 1984. It is the successor to the Motorola 68010 and is succeeded by the Motorola 68030.- Description :...
-based
Macintosh LCThe Macintosh LC was Apple Computer's product family of low-end consumer Macintosh personal computers in the early 1990s. The original Macintosh LC was released in 1990 and was the first affordable color-capable Macintosh. Due to its affordability and Apple II compatibility the LC was adopted...
. This was Apple's first attempt at a "low-cost" Mac, and it was such a success that, when subsequent models replaced the CPU with a 68030, a 68040, and later a
PowerPCPowerPC is a RISC architecture created by the 1991 Apple–IBM–Motorola alliance, known as AIM. Originally intended for personal computers, PowerPC CPUs have since become popular embedded and high-performance processors...
processor, ways were found to keep the PDS slot compatible with the original LC, so that the same expansion cards would continue to work.
Similarities to AGP
The
Accelerated Graphics PortThe Accelerated Graphics Port is a high-speed point-to-point channel for attaching a video card to a computer's motherboard, primarily to assist in the acceleration of 3D computer graphics. Since 2004, AGP has been progressively phased out in favor of PCI Express...
or AGP, which was the most widespread standard for connecting graphics cards to PC motherboards from 1997 until 2005, may be considered to be somewhere in-between a PDS and a bus. Like a PDS, there is no bus arbitration, so you can only have one AGP card per system; however, it works at a higher level than a PDS, in that it is CPU-agnostic, and AGP cards can be designed to work across Intel- or AMD-based PCs as well as Apple Macs and other computer platforms.
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