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Comment by PaulHoule

1 day ago

Well, it has 256 bytes of RAM which is basically a really big register file, and everything else goes in the 16kb of "video RAM" which you can read and write by poking at I/O registers. So it is not easy to program.

It's arguably the only 8-bit computer which has a really different architecture from the others. You could otherwise imagine pulling the SID chip off a C-64 and putting it on a TRS-80 Color Computer etc.

Sharing the main RAM with video was a weak point in computers of that time period because the video system stole many of the memory access cycles. Some recent retrocomputers that revisit that period like

https://www.c64-wiki.com/wiki/Commander_X16

have a full-size memory bank and a video RAM memory bank which is accessed through a port which can be pretty efficient because you can auto-incremement the address register and just write 1 byte to the port to write 1 byte to video RAM and repeat.

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PaulHoule

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HappMacDonald  1 day ago

Well I mean it fits in with the 8-bit era machines as far as performance but that CPU was absolutely 16 bit.

  • PaulHoule  1 day ago

    16-bit registers, operations, etc. yeah. A bigger machine of the TM9 series would be more like a PDP-11.

    • FarmerPotato  2 hours ago

      The 9900 was exactly contemporary with the LSI-11 CPU. Both TI and DEC were taking advantage of new LSI gate-counts to move discrete TTL CPUs into one chip.

      The 990 series of minicomputers were competing with PDP-11s (Though DEC had highest market share, I believe 33% of the whole mini market?)

      The 9900 was condensed in 1975 and went into the low-end 990/4. The higher end 990/9 and 990/10 were always going to be discrete TTL as the 9900 didn't support memory protection or mapping to the 2MByte total address space.

      TI was always conscious of not challenging IBM head-to-head in minicomputers. Internal memos always projected TI's plan for its minis to occupy a space well below the latest IBM mainframes. From 1980, the planned 990/12 would arrive just as IBM delivered more compute power in their low-end... this was intentional, supposedly because IBM was the chief driver of TI's transistor business!