 | This article has multiple issues. Please helpimprove it or discuss these issues on thetalk page.(Learn how and when to remove these messages) (Learn how and when to remove this message)
|
Aprocessor direct slot (PDS) is a slot incorporated into many olderMacintosh models that allowed direct access to the signal pins of a CPU, similar to the functionality of alocal bus inPCs. This would result in much higher speeds than having to go through a bus layer, such asNuBus, which typically ran at a slower 10 MHz speed.[1]
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 witharbitration 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 alocal bus.
Thus, PDS slots tended to be CPU-specific, and therefore a card designed for the PDS slot in theMotorola 68030-basedMacintosh SE/30, for example, would not work in theMotorola 68040-basedQuadra 700.
The one notable exception to this was the PDS design for the originalMotorola 68020-basedMacintosh 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 aPowerPC processor, Apple found methods to keep the PDS slot compatible with the original LC, so that the same expansion cards would continue to work.
The SE "System Expansion" slot, introduced in theMacintosh SE in1987, was the first processor direct slot, using a 96-pin Euro-DIN connector to interface with theMotorola 68000 processor. This slot was also used in theMacintosh Portable.[2]
The L2cache slot of theMacintosh IIci, introduced in1989, was a32-bit version of a PDS which used a 120-pin Euro-DIN connector to support theMotorola 68030 processor. This slot also appeared in theIIvi, andIIvx. These allowed for 3rd party companies, such asDayStar Digital, to develop processor upgrades that did not require the removal of the CPU.[1]The IIci cache slot is different from the other PDS slot as it doesn't have provision for external connectors,[3] and it does not include an interrupt request signal, thus limiting its use. Its pin configuration is also completely different from the one in most later MC68030-based non-LC Macintoshes.[4]
TheMacintosh SE/30 included a PDS slot that uses the same 120-pin Euro-Din connector as the IIci, but a different pin configuration.[5] The primary clock is the 16 MHz clock for the CPU. Unlike the IIci cache slot, it includes three interrupt request signals. There is also provision in the case for external connectors, so it was commonly used for graphic or network devices.TheMacintosh IIsi included a motherboard slot very similar to the SE/30,[6] although clocked at 20 MHz like the onboard MC68030. This slot was not intended for direct use, Apple instead offered two adapter cards[7] with a second connector mounted at a right angle (so the board would be parallel to the motherboard). One card provided aNuBus slot, while the other was essentially a pass-though configuration enabling a slot very similar to the IIsi, but with only one interrupt signal supported. Both cards also included an MC68882 FPU, which was not present on the IIsi motherboard.
TheMacintosh IIfx, introduced in 1990, included a PDS that was almost identical to the SE/30 and IIsi,[8] but not entirely. In particular, the clock signal is running at 20 MHz like the IIsi but the CPU is running at 40 MHz. The clock signal is also on a different pin from the IIsi and SE/30. Unlike other PDS, the connections to the processor signals are not direct, with intermediate buffering needed to handle the different clocks based on the physical address requested - some address would be accessed with the 20 MHz clock, and some other with the (not directly available on the slot) 40 MHz CPU clock ("fast slot space").[9] The physical space available for the board was also different from the SE/30 and IIsi.
The LC slot, introduced in1990, began as a PDS for theMotorola 68020 /68030 processors in theMacintosh LC /LC II. It only supported the asynchronous cycle of the MC68020, and did not connect all address signals, though it did connect all 32 data signals.[10] The 96-pin Euro-DIN connector is similar to the SE slot connector, but the two are completely incompatible. Latter models added 18 more pins through a notched in-line extension to support the full MC68030 bus (synchronous cycle, all address lines, clock both from the CPU and backward-compatible 16 MHz), while retaining backwards compatibility with older cards. This configuration proved to be so popular for Apple'sPerforma line that later 68040 such as theMacintosh LC 475 andPowerPC-based versions were essentially emulating the 68030 pin signals for the LC slots that they inherited.[2][11]
TheMacintosh Quadra series was introduced in1991 with a new PDS for theMotorola 68040 processor which was in-line with one of theNuBus slots. TheQuadra 605 andQuadra 630 were exceptions which used the full 114-pins version of the LC slot. Both allowed forPowerPC upgrades, including through the "Ready for PowerPC upgrade" program, using Apple'sMacintosh Processor Upgrade Card.[2]
ThePowerBook Duo line was introduced in1992 with a unique68030-based connector that could allow the subnotebook logic board to communicate with an array of desktop docking systems, some of which could be upgraded withfloating-point units. Because of the complexity of largerDuo Docks,NuBus was used to manage parts of the subsystems.[2]
First generationPower Macintosh systems withNuBus architecture, such as the6100,7100, and8100, included a PDS that was used for high-speed AV cards. It was later used by third-party manufacturers to supportPowerPC G3 andG4 upgrades.
High-end second generationPower Macintosh systems withPCI architecture, such as the7500 through9600, had theirPowerPC 601 and604 processors on daughtercards which could be swapped out forPowerPC G3 andG4 upgrades.
Mid-rangePower Macintosh systems based onPowerPC 603e processors withPCI architecture, such as the5400,5500, and6360 through6500, featured an L2cache slot which provided direct access to the CPU. This allowed enterprising third-party manufacturers to buildPowerPC G3 upgrades for this slot.
More recent Macs have such high processor speeds that a PDS would not be practical and instead adoptedPCIe andThunderbolt (interface).[12] The last implementation resembling such a slot by Apple is the processor tray connector in the 2009 to 2012Mac Pros. More recent models have hadIntel Xeon processors socketed directly to the logic board.
Some of the text was originally copied fromProcessor direct slot at Apple Wiki, which is released under aCreative Commons Attribution-Share Alike 3.0 (Unported) (CC-BY-SA 3.0) license.
