IBM PS/2 model 25 question

[linuxlove]

My PS/2 has a Simens 8086-2 in it which runs at 8MHz. What I'm wondering is, did a stock 25 come with a 4.77MHz 8086 or an 8MHz one?

 

[billdeg]

If I were to guess ('cause I don't feel like opening my mod 25), that's the std. 8086 chip that came with the model 25, it's not a souped up model. It is possible that with an improved 8086 the ROMs are accessed at the full 8086 speed, and the some of the RAM--Processor swapping is full speed (everything but video), giving the system an effective clock speed that is closer to 6mhz.
Bill

 

[Marrr]

Model 25 and Model 30 both came with 8 MHz 8086-2.

 

[IBMMuseum]

Model 25 and Model 30 both came with 8 MHz 8086-2.

Seconded. The 8MHz 8086 was stock on the (8086 versions) Model 25 and 30. 80286 versions of the same units ran at 10MHz (in a newsgroup posting I had it that pin 39 of the NPU socket was tied to ground, to run the 80287 at 6.66MHz, but I need to double-check that). There was even a version of the Model 25 that had a 386SX, run at 16 or 20MHz (officially it was at 16MHz, but some models, with no other reference than looking at the crystal and CPU inside, were run at 20MHz).

There were a few planar upgrades for the Model 25 or 30 (not the 8086 version of the Model 30, as its planar was a slightly different form factor) systems, mainly from Reply and PC Enterprises. Usually it was to go up to a 486DX4 level. William Walsh probably has them documented the best.

 

[digger]

I wonder... Did the on-board MCGA adapter on the 8086-based models have a 16-bit bus interface with the CPU?

Since the PS/2 Model 25 and Model 30 were only ISA based and the 8086 versions thus (I assume?) had only 8-bit ISA slots, an internal 16-bit video bus would at least have given those system an advantage in terms of video graphics performance.

 

[IBMMuseum]

I wonder... Did the on-board MCGA adapter on the 8086-based models have a 16-bit bus interface with the CPU?

Since the PS/2 Model 25 and Model 30 were only ISA based and the 8086 versions thus (I assume?) had only 8-bit ISA slots, an internal 16-bit video bus would at least have given those system an advantage in terms of video graphics performance.

I doubt if the MCGA interface is 16-bit, when the VGA upgrade card for the 8086-based Model 30 is 8-bit (in fact I even wonder the bus width of planar VGA on the other PS/2s), but I will look it over...