8 Bit machines?

[robcfg]

In the text file linked in the wikipedia article, I found this:

Although all registers are still just 8 bits wide, the 65CE02 provides
      some 16 bit instructions, mainly in Red-Modify-Write instructions:
                     
        ASW $nnnn   CB  Arithmetic Shift Left Word
        DEW $nnnn   C3  Decrement Word
        INW $nnnn   E3  Increment Word (ERROR IN 64NET.OPC?)
        PHW #$nnnn  F4  Push Word
            $nnnn   FC
        ROW $nnnn   EB  Rotate Right Word


      Note that some of these instructions support the 16-bit rotate/shift
      instructions of the 65SC02 mentioned above.

There was also a 6502 16-bit upgraded version that was the 65816, which was used on the SNES.


And of top of that, the R800 in the turboR ran at 7.16 mhz and it took 4 times less clock cycles to execute the instructions.

[sigh]

In the text file linked in the wikipedia article, I found this:



There was also a 6502 16-bit upgraded version that was the 65816, which was used on the SNES.


And of top of that, the R800 in the turboR ran at 7.16 mhz and it took 4 times less clock cycles to execute the instructions.

Ahhhh, so it was more like a hybrid again like the MSX Turbo R and PC engine. Made sense to scrap it and build the reputation on Amiga's to some extent.

Found a good few demos of the C65 in action:
http://www.youtube.com/watch?v=mL4iX_iuBO8&feature=related

...and that one sold for 10,000 euro!

Edit: Further lengthy description on the C65 chip:
http://archive.6502.org/datasheets/mos_65ce02_mpu.pdf

[MacDeath]

Commodore 65

lol it looks like a CPC664/6128 setting...

[steve]

The z80 has some 16bit instructions and yet it is an 8bit processor.

The 65ce02 with some 16bit instructions is still an 8bit processor.

The 68000 with 32 bit registers and instructions is a 16BIT processor.

[fano]

It is not easy to classify CPU as 8 or 16 bits.Taking a look to the chip pinout can give an answer 

For example the SNES cpu is named as a 16 bits CPU but its data bus width is 8bits so does SNES is a 8 or a 16 bits machine ?

[fano]

Were 8 bit "duocore" ever crafted ?

I remember Amstrad Cent Pour Cent spoke (an showed a picture) about a double Z80 CPC at TITUS software compagny.I can not remember exactly the issue but that was an article about TITAN if my memory is not too bad.

[redbox]

For example the SNES cpu is named as a 16 bits CPU but its data bus width is 8bits so does SNES is a 8 or a 16 bits machine ?

You are right, it is difficult.  The SNES would definitely be classed as 16-bit though 

I always thought the PC Engine was 8-bit and the best one there is, but it appears that is debatable.

The one that always made me smile was the Atari Jaguar because they said it was "64-bit" but really that was only the data bus size too if I remember correctly.

[CPCLER]

Hi There

I thought that the amount of bits a given CPU is, depends on how many bits the CPU can move during a cycle (The actual time it takes to execute a cycle depends on the clock frequency of the system, so in theory a 4Mhz 8bit CPU would be just as fast as a 2Mhz 16bit CPU)

This way it has nothing to do with either width of the data nor width of the address bus!

But maybe i remember wrong!!

Regards,
CPCLER

You are right, it is difficult.  The SNES would definitely be classed as 16-bit though 

I always thought the PC Engine was 8-bit and the best one there is, but it appears that is debatable.

The one that always made me smile was the Atari Jaguar because they said it was "64-bit" but really that was only the data bus size too if I remember correctly.

[steve]

To my mind the most logical way of categorizing a processor is by the number of bits a processor can "crunch" in one machine cycle, which is the size of the ALU.

External databus size is irrelevant, the 8088 is a 16bit processor with a 16bit internal databus and an external 8bit databus.

[fano]

Yes , ALU is another important thing too.
For me , it is important as the bus width as a CPU is not alone in a system , if the data to read/write is larger than the bus , it will need to process multiple operations.Same thing , if the operation size is larger than ALU , that will be needed to process several operation.

[AMSDOS]

Commercially 8-bit computers may no longer be built, though Hobbyists who are using the Internet to show off their 8-bit computer creations. I recall one site having a Z80 based machine with the mainboard the size of a 3.5" Disk Drive and could indeed run CP/M with the necessarily hardware, unfortunately I can no longer find the site!    Since it's well known that 8-bit computers began as a DIY project which you would build, it's only fair to say that DIY has somehow keep a bit of a scene for that sort of thing to happen! 

[Sykobee (Briggsy)]

Yeah, there's a few new 8-bit designs using the Z80, some RAM and a more modern Atmel AVR for other logic. Or even just the AVR (as it is a full 8-bit RISC at 16MHz) http://www.bbc.co.uk/news/technology-13201254


As for the bittiness of a CPU, I think these days you would look at the register size first, then the ALU width, and lastly the data bus width. You would also want to consider things more holistically in terms of the features, etc.


68000 - 32-bit registers, 16-bit ALU, 16-bit data bus and 24-bit address bus (but address registers were 32-bit). It's always been referred to as a 16/32 bit processor. The Amiga/ST/Megadrive labelled themselves 16-bit, but that's also because of the support chips.
68008 - 32-bit registers, 16-bit ALU, 8-bit data bus and 20-bit address bus (IIRC)
Z80 - 8 bit registers with pairing capability and some 16-bit instructions, 8-bit ALU, 8-bit data bus, 16-bit address bus. The Z180/R800 showed that the instruction set and design could be extended to full 16-bit. The eZ80 extends it to 32-bit IIRC.
6502 - 8-bit registers, 8-bit ALU, 8-bit data bus, 16-bit address bus. Again, extended later on.


The downside of having an ALU width half the size of the registers was merely that instructions took longer to execute when operating on the full register width. Therefore it's just an implementation issue - saving transistors at the cost of instructions per clock.


With that in mind, was the Z80 8-bit or 16-bit? Holistically you would say it's 8-bit - it's designed from an 8-bit heritage, the registers are all 8-bit accessible, the 16-bit instructions take a lot longer to execute, it only addresses 64KB, etc. But it's more 16-bit than the 6502!

[AMSDOS]

Yeah, there's a few new 8-bit designs using the Z80, some RAM and a more modern Atmel AVR for other logic. Or even just the AVR (as it is a full 8-bit RISC at 16MHz) http://www.bbc.co.uk/news/technology-13201254


As for the bittiness of a CPU, I think these days you would look at the register size first, then the ALU width, and lastly the data bus width. You would also want to consider things more holistically in terms of the features, etc.


68000 - 32-bit registers, 16-bit ALU, 16-bit data bus and 24-bit address bus (but address registers were 32-bit). It's always been referred to as a 16/32 bit processor. The Amiga/ST/Megadrive labelled themselves 16-bit, but that's also because of the support chips.
68008 - 32-bit registers, 16-bit ALU, 8-bit data bus and 20-bit address bus (IIRC)
Z80 - 8 bit registers with pairing capability and some 16-bit instructions, 8-bit ALU, 8-bit data bus, 16-bit address bus. The Z180/R800 showed that the instruction set and design could be extended to full 16-bit. The eZ80 extends it to 32-bit IIRC.
6502 - 8-bit registers, 8-bit ALU, 8-bit data bus, 16-bit address bus. Again, extended later on.


The downside of having an ALU width half the size of the registers was merely that instructions took longer to execute when operating on the full register width. Therefore it's just an implementation issue - saving transistors at the cost of instructions per clock.


With that in mind, was the Z80 8-bit or 16-bit? Holistically you would say it's 8-bit - it's designed from an 8-bit heritage, the registers are all 8-bit accessible, the 16-bit instructions take a lot longer to execute, it only addresses 64KB, etc. But it's more 16-bit than the 6502!

Interesting the 68008 is 8bit cause it's Bus will only allow it!    Surely if it only has an 8bit data bus though has 32-bit registers, 16-bit ALU and 20-bit address bus, there must be some advantage in having those things?

[steve]

Interesting the 68008 is 8bit cause it's Bus will only allow it!    Surely if it only has an 8bit data bus though has 32-bit registers, 16-bit ALU and 20-bit address bus, there must be some advantage in having those things?

The advantage of the 8-bit bus is that a computer system is cheaper to manufacture than a 16-bit bus system, yet the 68008 can execute 68000 code only 30% slower then the 16-bit 68000, and therefore a reasonable compromise between speed and cost.

If a version of the Z80 were made with a 16 or 32 bit data bus, it would execute code faster, but would still be an 8-bit processor.

[AMSDOS]

The advantage of the 8-bit bus is that a computer system is cheaper to manufacture than a 16-bit bus system, yet the 68008 can execute 68000 code only 30% slower then the 16-bit 68000, and therefore a reasonable compromise between speed and cost.

Yeah there probably wasn't too many high end businessmen back then that wanted maximum performance and would have it at any cost! 

If a version of the Z80 were made with a 16 or 32 bit data bus, it would execute code faster, but would still be an 8-bit processor.

I guess that would be harder to do if you had limited space on the mainboard, so for something like a Nintendo Gameboy I'm presuming it only has 8bit data bus too

[MacDeath]

Weren't some Z80 built to run at (impressive) 16mhz ?

The later PCWs (PCW16 ?) got them if I remember well...

[steve]

Yeah there probably wasn't too many high end businessmen back then that wanted maximum performance and would have it at any cost! 

The Sinclair QL used a 68008, it was also manufactured as the ICL "one per desk" and sold to the corporate world, it was functionality that counted then, speed came later, in fact few people demanded more speed, what they had was fast enough, but they were persuaded that getting something faster would increase productivity, and they have been falling for the same lie ever since.

[steve]

Weren't some Z80 built to run at (impressive) 16mhz ?

The z80 is currently available in speeds up to 33mhz last time I looked, and there is now the eZ80 which runs at up to 50mhz.

A single board computer is available called the v6z80p+ which has a 16mhz z80, blitter, VGA, sound and 1152 KB ram for under £100.

[AMSDOS]

The Sinclair QL used a 68008, it was also manufactured as the ICL "one per desk" and sold to the corporate world, it was functionality that counted then, speed came later, in fact few people demanded more speed, what they had was fast enough, but they were persuaded that getting something faster would increase productivity, and they have been falling for the same lie ever since.

I always recall reading a description about that machine where a Sinclair QL was expandable to 640k and that was in a book done in 1984! (Probably allows more these days!  ) Unexpanded the machine had 128k, would have been a costly thing back then just to have the full 640k!    (But then an Apple Lisa which came out in 1983 had 1 Megabyte and had a cool 10 grand!  ).I presume it would be able to use CP/M-68k, though I'm guessing it had it's own OS/BASIC included?

[MaV]

Yeah there probably wasn't too many high end businessmen back then that wanted maximum performance and would have it at any cost! 

It's those effin businessmen in particular that don't need any kind of max performance. We've had the equivalent of Word, Excel and Powerpoint already back then, and they worked ok. Performance is needed for games, technical jobs or video and sound editing and the like.

Even non-technical people are starting to realize that 2GB, 4GB, or even 8GB of RAM doesn't make much of a difference for everyday tasks anymore. The only reason I can come up with to use 8GB would be virtual machines.
It also makes no sense buying ever faster processors these day, when the main bottleneck of computers is the hard-drive.


Back to the topic:

Personally, I prefer to give the data bus the highest priority. My taxonomy of processors would not differ much from Briggsy's however. You really can't sum up a processor better than to give at least those for values (data bus width, alu width, register width, address bus width).

MaV

[AMSDOS]

It's those effin businessmen in particular that don't need any kind of max performance. We've had the equivalent of Word, Excel and Powerpoint already back then, and they worked ok. Performance is needed for games, technical jobs or video and sound editing and the like.

Completely agree! 

Even non-technical people are starting to realize that 2GB, 4GB, or even 8GB of RAM doesn't make much of a difference for everyday tasks anymore. The only reason I can come up with to use 8GB would be virtual machines.

Having more RAM & Speed is only a further excuse for more sloppy programming.

It also makes no sense buying ever faster processors these day, when the main bottleneck of computers is the hard-drive.

I've had 3 Hard Drives die on me and the Hard Drive that's in my old Pentium is on it's last legs! (Fortunately I was able to back up all the important stuff from it!). It really hurts when they go though, if someone comes up with a modern Hard Disk (without the problems Hard Drives have) with ISA interface I'd be quite interested! 

[Gryzor]

Regarding performance, it depends. Try telling my entire marketing department, running Photoshop on each workstation, that they don't need more than 1GB

[MacDeath]

In the era, many companies had a programmer to manage the computers they may have.

I mean, so many companies (not especially the biggest) had to produce their own softwares... because "easy to run" softwares weren't that "easy to run" and ready to use solution not yet the norm (as so many different computers with uncompatibles specs existed...).

So yep, the "Computer manager" (often called the Alpha Geekz) often asked for better machines.


So while nowadays, getting a "biggest" is just some ego trip for white collars...(compensate) unless "techlabs" and so on...

At the time, language like Cobol were actually used in so many companies (banks ?).
Having +64K, disk drives and Colour monitor could really be helpfull...

Hence CPC6128 was really some bizness stuff at first.
Just imagine if it were released 3 years before...

[redbox]

Regarding performance, it depends. Try telling my entire marketing department, running Photoshop on each workstation, that they don't need more than 1GB

And there in lies the problem... 

[sigh]

I must admit that I do find it very annoying when I'm at work using 3DS MAX and task manager tells me that it's alreday using over 400 MB before I've even opened a file!!!