ZX Spectrum 'v' MSX

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By Grauw

Ascended (9912)

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27-04-2021, 23:34

Manuel wrote:

Someone in the comment thread claims that the Spectrum has a bitmap mode (and the MSX has not). Is that true? Or is the Spectrum similar to screen 1/2 with more limitations?

It’s as much a bitmap mode as screen 2 is a bitmap mode in the default layout used by MSX-BASIC where the pattern name table is filled with 3x 0-255. The Spectrum pixel layout isn’t linear either so there’s no convenience there on either side.

But because on MSX screen 2 is a pattern mode, when the level is built from a tile map the MSX is much more bandwidth-efficient. MSX allows you to change the entire screen with just 768 byte writes. On the Spectrum you have to rewrite the entire screen bitmap and colour data (6912 bytes) because you can’t reorder the 8x8 blocks.

The situation where the MSX uses more CPU bandwidth is only applicable when the screen is used as a bitmap (due to the higher colour resolution) without using the pattern tiling capabilities. Obviously, all Speccy ports are coded for a bitmapped memory layout, so the pattern mode functionality is not used and you end up with those games needing more CPU power and running slower on MSX.

By erpirao

Paragon (1190)

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27-04-2021, 23:12

sc3 is bitmap isn´t?

By Grauw

Ascended (9912)

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27-04-2021, 23:18

Nope, even screen 3 is a pattern mode, it has a separate name and pattern table.

By Timmy

Master (143)

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29-04-2021, 15:35

djh1697 wrote:

Clive Sinclair stated that the spectrum was 2 to 3 times more powerful than the MSX, an interesting, new video, about how it wasn't!

I watched that video now, and I think that the conclusion was that it was just poor journalism back in the days. Tongue

Then again, if he did heard about that an MSX computer was like a Z80 processor with a VDP chip designed in 1979, then yes, he would probably be right saying that it's being old and less powerful. I wouldn't be surprised if he actually did looked at that VDP chip before designing the Spectrum (or the ZX80/81).

It was also out of his budget because the VDP had its own dedicated 16K of RAM, in a time when RAM was really expensive. The Spectrum 16K had only 16K of RAM in total, and that was the reason why he could sell the it for a much lower price.

In hidsight, I think he didn't really need to worry about the MSX at the time, as the MSX wasn't even in the price range of the Spectrum.

*) The MSX VDP chip is a nice chip, but it was still a 1979 chip. Even the C64 that was already on the market, at the same price as the MSX, had a VIC-II designed in 1981, with hardware smooth scrolling, and 8 sprites per scanline (according to Wikipedia).

By AxelStone

Prophet (2963)

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29-04-2021, 15:52

Timmy wrote:

In hidsight, I think he didn't really need to worry about the MSX at the time, as the MSX wasn't even in the price range of the Spectrum

I agree MSX and Spectrum had price ranges completely different. In some situations, the dedicated VRAM was a problem for loading cassette software because a lot of MSX1 models had 48kb split in 32Kb RAM + 16kb VRAM, so a lot of converted software didn't fit in 32kb.

By gdx

Enlighted (4498)

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29-04-2021, 16:16

It's pretty funny to see someone try to make the ZX Spectrum look better with only one argument (since there isn't any other).

By santiontanon

Paragon (1420)

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29-04-2021, 16:29

Even if back in the day I would have fought tooth and nail to defend the MSX, with a bit more perspective, there are actually things that the Spectrum does better, and things that the MSX does better (I'm talking about first generation MSX only). For example, the Z80 in the spectrum is indeed faster than the MSX one, since there's wait states introduced in most instructions in the MSX. So, even if they run at the same frequency, the Spectrum one ends up being about 10%-20% faster (so, not 2 - 3 times, but indeed faster). Also, having VRAM as part of RAM open so many possibilities, which are very hard to replicate on an MSX (e.g., many spectrum games have lots of particle effects, since writing a single byte to VRAM is cheap, where as in the MSX that's more expensive). On the other hand, there's lost of things the MSX does better, of course, like the hardware sprites, the increased resolution of color attributes, the PSG (which was only added on Spectrum in the 128k version, which I think should be compared with the MSX2 given they are both from 1985), etc.

So, all in all, I am very fond of both machines, and I think these are all just historical curiosities Smile

By gdx

Enlighted (4498)

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29-04-2021, 17:00

santiontanon wrote:

For example, the Z80 in the spectrum is indeed faster than the MSX one, since there's wait states introduced in most instructions in the MSX.

The frequency is slightly faster too but MSX design is more reliable. It doesn't have these bugs:
https://sinclair.wiki.zxnet.co.uk/wiki/ZX_Spectrum_16K/48K

Shared RAM also greatly limits the programs size and hardware evolution.

By lintweaker

Champion (406)

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29-04-2021, 17:37

I thought that the spectrum was actually slowed down by the PLA to allow for the main memory to be used to display an image? Or I am mixing things up with another machine from that era?

By PingPong

Prophet (3738)

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29-04-2021, 21:50

It does depend. What does it mean bitmap mode?
To me both have bitmap mode, the difference is the corrispondence between memory addresses and pixels.

Screen is divided in three sections like is the screen 2 mode of vdp.

For Each Section you do:

Pass [A]
the first scanline (Y=0 of the section) of the section of spectrum is 32 bytes in length and describe the pixels like a msx2 screen 5 does, except it does use 1 bit per pixel instead of 4!
next 32 bytes are 8 pixels down
next 32 bytes are 8 pixels down
... will continue until you reach the end of a each 1/3 section in Y direction.

when you reach the end of each section, you restart to top, this time you process the second scanline (Y=1 relative to the section) and repeat [A]
when you reach the end of each section, you restart to top this time you process the third scanline (Y=2 relative to the section) and repeat [A]

you continue [A] until 8 scanlines are filled in. So At this time you have the first section of the screen entirely filled.

the process will restart from beginning for the next section until you have filled the next two sections.

look at this: https://www.youtube.com/watch?v=sm09ssgSYiQ

As you can see it is straightforward to upload the zx spectrum layout to screen 2 vdp vram layout, i found a lot of zx spectrum that performs operations like the zx spectrum layout then do the converition on the fly while upload this to VDP Vram.

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