Processor Direct Slot
 | This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these template messages)
|
A processor direct slot (PDS) is a slot incorporated into many older
Overview
Typically, if a machine had bus expansion slots it would feature multiple bus expansions slots. However, there was never more than one PDS slot, as 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, making it closer in nature to a local bus.
Thus, PDS slots tended to be CPU-specific, and therefore a card designed for the PDS slot in the Motorola 68030-based Macintosh SE/30, for example, would not work in the Motorola 68040-based Quadra 700.
The one notable exception to this was the PDS design for the original Motorola 68020-based Macintosh LC. 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 PowerPC processor, Apple found methods to keep the PDS slot compatible with the original LC, so that the same expansion cards would continue to work.
History
SE slot (Motorola 68000)
The SE "System Expansion" slot, introduced in the Macintosh SE in 1987, was the first processor direct slot, using a 96-pin Euro-DIN connector to interface with the Motorola 68000 processor. This slot was also used in the Macintosh Portable.[2]
IIci slot (Motorola 68030)
The L2
IIfx PDS (Motorola 68030)
The Macintosh IIfx, introduced in 1990, included a PDS that was visually similar to the IIci slot, but differences in pinouts and bus mastering resulted in very limited use.[3]
LC slot (Motorola 68020/68030)
The LC slot, introduced in
Quadra PDS (Motorola 68040)
The Macintosh Quadra series was introduced in 1991 with a new PDS for the Motorola 68040 processor which was in-line with one of the NuBus slots. The Quadra 605 and Quadra 630 were exceptions which used a 32-bit version of the LC slot. Both allowed for PowerPC upgrades through the "Ready for PowerPC upgrade" program.[2]
Duo Dock connector (Motorola 68030 / NuBus)
The
Power Macintosh PDS (PowerPC 601)
First generation
PowerPC daughtercard slot
High-end second generation
PowerPC cache slot
Mid-range
More recent Macs have such high processor speeds that a PDS would not be practical and instead adopted
See also
References
Text was copied from Processor direct slot at Apple Wiki, which is released under a Creative Commons Attribution-Share Alike 3.0 (Unported) (CC-BY-SA 3.0) license.
- ^ a b "Mac IIci". lowendmac.com. Archived from the original on 2022-09-03. Retrieved 2022-09-03.
- ^ a b c d "PDS: The Processor Direct Slot". lowendmac.com. Archived from the original on 2022-09-03. Retrieved 2022-09-03.
- ^ "68kMLA". 68kMLA. Archived from the original on 2022-09-03. Retrieved 2022-09-03.
- ^ Macintosh LC III Developer Note (PDF) (Technical report). 2000. Archived from the original (PDF) on 21 July 2004. Retrieved 3 September 2022.
- ^ "One cable to rule them all: a look at Apple's retired connectors through the years". AppleInsider. Archived from the original on 2022-09-03. Retrieved 2022-09-03.
External links
- Pictures of several PDS cards at AppleFritter
- What kind of expansion or upgrade slots does my Mac have? at Mac FAQ
- Notes on PDS variations at Apple Wiki