Yep, but it lacks a MMU so memory protection and paging are going to require a lot of work. I think the only reason this is feasible at all is they're running the OS out of a ROM cartridge.

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jandrese 2 hours ago | parent | next [-]

The PDP machines that Unix was developed on had MMUs, which they needed because the 16 bit processors couldn't address the multi-megabyte address space the hardware supported.

I'm pretty sure the Centurion doesn't run Unix.

	▲	PaulHoule 39 minutes ago \| parent [-]
		The PDP-10 had an MMU similar to a modern MMU with page tables and such, the PDP-11 had an 8-segment-of-8kb MMU like what the TRS-80 Color Computer 3 had except the PDP-11 had a real supervisor mode and if a user mode program tried to change the MMU configuration it would fault.

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MBCook 2 hours ago | parent | prev [-]

Did the minicomputers of the time have MMUs?

I thought UsagiElectric showed a case where his Centurion didn’t, but I may be misremembering.

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McGlockenshire an hour ago | parent [-]

In fact the 9900 itself was used in an entire line of minicomputers that included a hardware memory map.

The 9900 is a single chip implementation of the CPU board in the TI 990. They even created a dedicated memory mapper chip to go along with the product line, though it is significantly different than the one in the minicomputer line.

(edit: the 990 was first built in the early 70s, memory mappers are quite old conceptually)

(edit 2: in fact the necessity of using a memory mapper is what killed the platform, and was one of the things that made the IBM PC team decline the 9900.)

Unfortunately I don't think that there is a reasonable way to perform real hardware-level memory protection with that chip alone. I'm working on a project documenting the genesis of the 99000 chips, which include a privilege bit in the status register, from the minicomputer line.

Essay forthcoming, and probably an OS. Maybe a year...

	▲	jecel 16 minutes ago \| parent [-]
		One chip that could be used as a memory mapper for the 9900 (but wasn't in the TI99/4A) was the 74LS670, which was used in the IBM 5150 PC to allow the 8237 DMA chip to access more than 64KB (a limit that wasn't a problem when used in a 8080 system).