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TI-99/4A vs ZX81

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Oh, there's no contest: the 99/4A. Aside for the fact that the '99 could do colors and sound and sprite-based graphics, you could actually plug in joysticks or play with a full-stroke keyboard, none of which was possible on a (stock) ZX81. I'm pretty sure that the 99/4A's commercial game library was also much larger. The only advantage the ZX81 had over the 99/4A was price, but even that advantage was gone as TI slashed the prices from 1982-1984.

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99/4A wins there, too (IMHO). The stock TI BASIC was slow and non-standard, but it was still more capable as a programming language than Sinclair BASIC, and it got several versions of Extended BASIC which expanded its capabilities even more.

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Anyone trying to compare the TI99/4a and ZX81 must not know what one of them is. :P

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Hardware wise, the TI is miles ahead of the ZX-80/81/TS-1000.
On Ahl's benchmark, the TI is actually faster than the ZX-81.
The TS-1000 in fast mode beats the TI by around a minute on that benchmark, and in slow mode the TS-1000 takes almost 17 minutes,

which is near the end of the list. A couple programmable calculators are slower..
If you just needed to do some number crunching the TS-1000 might be the way to go, but otherwise... nope.
The Spectrum and TS-2068 finish behind the ZX-80.
Just remember that benchmark is mostly just square and square root calculations.

It doesn't mean everything else will compare similarly.
FWIW, the 1MHz ish Microsoft BASIC 6502/6803 machines finish in under half the time of TI Extended BASIC.


Hardware wise, the Spectrum is okay for the original price, but the first models didn't have a sound chip, it doesn't have hardware sprites, and

The Spectrum doesn't have as flexible of graphics even without sprites.
One thing the Spectrum does have going for it, is that it was easy to develop for in assembly or other languages.
As a result, it's software library is larger than the TI's.

The BBC Micro doesn't have hardware sprites, but it makes up for it with CPU speed.
It uses the same sound chip as the TI, and it has good graphics.
BBC BASIC runs rings around most other machines speed wise.
It finishes Ahl's Benchmark in 21 seconds, almost 6 times faster than 1MHz Microsoft BASIC machines, and about 12 times faster than the TI.

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The ZX Spectrum has direct access to video memory, which makes isometric games (e.g. Knight Lore) and vector graphics games (e.g. Elite) possible.

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Anyone who ever, keyed in a program into the ZX81 membrane keyboard for several hours only to knock the 2k ram pack by mistake before it could be saved to tape, would never ask this question.

 

TPi8gE6.jpg

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The stock TI BASIC was slow and non-standard...

The issue is rather that it was pretty much ANSI BASIC, but nobody else was. Then it added some procedures you invoked with CALL, to handle machine specific things.

Extended BASIC has borrowed more from TI Power BASIC (used in the TI 990 mini computers). The capability to have named subroutines with parameter passing in TI Extended BASIC is pretty unique on that level.

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TI-99/4A vs ZX81

 

in terms of graphics and games

 

TI-99/4A wins.

 

how about BASIC, counting extensions

 

TI-99/4A wins.

 

okay, so quick question, how well does it stack up to the other sinclair computers, the BBc micro and ZX spectrum?

 

my mistake. but the question stands, ZX spectrum, how does it stack up?

 

TI-99/4A vs ZX Spectrum

 

In terms of graphics and games... Hardware graphics were somewhat similar. Software graphics and games achieved in the eighties. ZX Spectrum wins.

 

how about BASIC, counting extensions... Somewhat similar in the eighties, but ZX Spectrum wins.

 

:)

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The ZX Spectrum has direct access to video memory, which makes isometric games (e.g. Knight Lore) and vector graphics games (e.g. Elite) possible.

Other machines with the 9918 graphics chip (Colecovision, MSX) have isometric games.

As long as you can order your screen writes to match the graphics chip, you can write to the screen pretty fast.

You wouldn't have seen anything like that on the TI in the 80s because the TI didn't come with enough CPU RAM.

I don't know if the TI is fast enough to pull off all isometric games, but titles like Batman should be easy for it.

Most isometric games only have a few moving objects on screen at once.

 

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One thing the Spectrum BASIC has the TI doesn't is support for bitmapped graphics.
You have to load a 3rd party program to do that with the TI. This came up in the Fedora 3D plot thread.

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Other machines with the 9918 graphics chip (Colecovision, MSX) have isometric games.

As long as you can order your screen writes to match the graphics chip, you can write to the screen pretty fast.

You wouldn't have seen anything like that on the TI in the 80s because the TI didn't come with enough CPU RAM.

I don't know if the TI is fast enough to pull off all isometric games, but titles like Batman should be easy for it.

Most isometric games only have a few moving objects on screen at once.

 

 

Yes but I believe the MSX can write almost twice as fast to the VDP than the TI because of the faster CPU, and still the MSX games appear to be slower than the Spectrum counterparts. I shall be the last person to say something is impossible on the TI, but there's a striking lack of these games on the TI.

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An MSX computer would use the Z80A CPU, doesn't it? Weren't they clocked at 1 MHz back then? That would hardly make them faster than even the TMS 9900, especially not if some more advanced math was also involved.

I remember the Z80 had internal states, that typically took 3-6 clock cycles, and more complex instructions could last several internal state cycles.

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An MSX computer would use the Z80A CPU, doesn't it? Weren't they clocked at 1 MHz back then? That would hardly make them faster than even the TMS 9900, especially not if some more advanced math was also involved.

I remember the Z80 had internal states, that typically took 3-6 clock cycles, and more complex instructions could last several internal state cycles.

 

Wikipedia says 3.58 MHz in the MSX and 3.5 MHz in the ZX Spectrum.

mips.png

 

:)

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How are the MIPS derived? Done by measuring a sample program execution time, or by calculating cycle times? I mean, the MPY and DIV are quite heavy, but are not even included in some (all?) 8-bit instruction sets.

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Still, MPY and DIV are efficient, compared to doing it the shift and add/subtract way.

The large amount of "registers" in the TMS 9900, plus the memory to memory architecture also implies that sometimes a single instruction in the 9900 do the same as several in an 8-bit CPU.

 

Like

Load byte to accumulator from memory 1L

Add byte in memory 2L

Store accumulator in register 2L

Load byte to accumulator from memory 1H

Add one if carry

Add byte in memory 2H

Store accumulator in memory 2H

 

In the TMS 9900 this is done by

A @memory1,@memory2

 

It doesn't matter if you can do twice the number of instructions in the same time if you need seven. Now some 8-bit CPU can do 16-bit arithmetic, which makes them more efficient, but the principle stands.

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Yes but I believe the MSX can write almost twice as fast to the VDP than the TI because of the faster CPU, and still the MSX games appear to be slower than the Spectrum counterparts. I shall be the last person to say something is impossible on the TI, but there's a striking lack of these games on the TI.

Keep in mind that if you can use some hardware sprites, you don't need to perform as many video writes as the Spectrum.

Here are the MSX and Spectrum versions of Batman. There doesn't seem to be a difference in speed.

https://www.youtube.com/watch?v=dZvH1oNLQD4

 

An MSX computer would use the Z80A CPU, doesn't it? Weren't they clocked at 1 MHz back then? That would hardly make them faster than even the TMS 9900, especially not if some more advanced math was also involved.

I remember the Z80 had internal states, that typically took 3-6 clock cycles, and more complex instructions could last several internal state cycles.

MSX is clocked at 3.58 MHz.

 

 

The Z80 has a pretty high number of clock cycles per instruction.

Instead of 2 to 4 clock cycles per instruction like the 6502 it's averaging around 9 to 14 but it depends on what you are doing.

MSX also adds additional wait states, around 1 or 2 cycles per instruction.

This puts the Z80 at a similar number of clock cycles per instruction to the 9900.

The difference in clock speed makes the Z80 a little faster.

The big difference is the OTIR block output instruction that transfers the bytes to the VDP on the Z80.

It requires 23 clock cycles per byte on MSX.

The equivalent three instruction loop on the 9900 is something like 34 clock cycles.

With the difference in clock speed the TI is just over half as fast as MSX, for writing to VDP RAM.

Slower if you are running from 8 bit memory.

 

You might be able to start writing to the VDP a little faster with the 9900 due to the 9900's ability to switch register files
where the Z80 might require saving an restoring registers... but the Z80 also has an alternate register set, so it depends on the code.

 

The thing is, it's a question of is the 9900 fast enough, not how much faster the Z80 is.

If you only need to switch and move hardware sprites once you are on a level, that's one thing, if you try to draw everything like the Spectrum version,

it's a lot tougher. I think it's just going to depend on the game.

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Still, MPY and DIV are efficient, compared to doing it the shift and add/subtract way.

The large amount of "registers" in the TMS 9900, plus the memory to memory architecture also implies that sometimes a single instruction in the 9900 do the same as several in an 8-bit CPU.

...

 

It doesn't matter if you can do twice the number of instructions in the same time if you need seven. Now some 8-bit CPU can do 16-bit arithmetic, which makes them more efficient, but the principle stands.

If you are dealing with floating point, you probably aren't using the integer multiply and divide instructions.

I don't know the guts of the TI BASIC math library, but I know Microsoft doesn't take advantage of the multiply instructions on the 6803 and 6809.

 

Edited by JamesD

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