8-bit

Was 8-bit Atari (6502) faster than IBM PC (8088)?

  • by

I was silent for a while as some things required my attention more than old computers. We extended the list of implementations of our Sieve Benchmark and it now supports even 6502. It was developed on Atari 800XL without any modern hardware or software (it’s written in ATMAS II macro-assembler). And it was a pain.

We all remember the lovely days of being young and playing with these simple computers, where programming was often the best way to spend time. These nostalgic memories don’t say the truth how horribly inefficient the development was on these machines in comparison with what came a decade later. David told me that his productivity was about 20 times lower in comparison with developing an assembly program of similar complexity and size on PC. These were one of the biggest reasons for your entertainment:

  • It was easy to fill whole available memory with the source code text. There was a situation when only 100 characters could be added to the text buffer, but about 2000 were needed. That caused that multiple parts were optimized for source code length (except, of course, the sieve routine itself, which was optimized for speed).
  • At the end, it was necessary to split the source code into two parts anyway.
  • Unlike with PCs, the Atari keyboard doesn’t support roll-over on standard keys. It is necessary to release the key before pressing another one (otherwise the
    key-press is not properly recognized).
  • Having a disk drive was a big advantage over tapes. However, the implementation on Atari was very slow and everything took incredible amount of time. Boot into editor? 20 seconds. Loading the first part of the source code? 5 seconds. Loading the second part? 30 seconds. Storing it back? 60 seconds (for just 17 KB). You needed about 160 seconds before trying to run the program after every larger change (including 20 seconds for compiling). Often a minute
    more if the program crashed the whole computer.

Although David never started to use “modern” features like syntax highlighting and code completion and he still programs mostly in the 80×25 text-mode, he said that this was too much for him so I don’t think we will repeat this again soon.

Regarding the results: A 1.77-MHz MOS 6502 in Atari 800XL/XE (PAL) required about 66 CPU cycles to go through a single inner-loop step. If graphics output was disabled during the test, this decreased to just 49 CPU cycles. A 4.77-MHz Intel 8088 needed about 73 CPU cycles to do the same. Thus, 6502 is faster if running on the same clock.

On the other side, the original IBM PC is clocked 2.7x higher than the Atari and 4.7x higher than other important 6502 machines (Apple IIe, Commodore 64). Thus, IBM PC was at least twice as fast in this type of tasks (similar to compiling, XML parsing…). I’m not surprised, but it is nice to see the numbers.

Interestingly, the heavily optimized assembly code running on Atari provides the same performance as compiled BASIC (MS QuickBasic 4.5) running on 20MHz 386DX (interpreted version would be three times slower). This was one of the fastest BASICs out there so it gives you good perspective on how these high-level languages killed the performance back then. David spent a lot of time optimizing the code for both CPUs and used the available tricks for each architecture (like self-modifying code…). If you feel that your favorite CPU should have been faster, you can download the project folder and check the source code. If you create a faster version, please send it to me (but please read the README first, especially the part called “Allowed tricks”).

Also if somebody is able to port the code to Commodore 64, it would be nice to compare the results with Atari (only the disk access, timer and console input/output need to be rewritten). Any expert/volunteer?

Sieve Benchmark download

Vintage Computers at Work

  • by

We prepared a small room with old computers as a part of a bigger event at work. After careful consideration, we selected Atari 800XL and Commodore Amiga 500 for the contest purposes. Atari was running Space Invaders and each visitor played with the highest difficulty (three lives, level 12). For Amiga, we chose Pinball Dreams and the goal was to get the highest score using just a single ball.

To make the room more appealing, we brought several old computer magazines and 80s props. Curious visitors could also experience ZX Spectrum+ with the Who Dares Wins game. The feedback on our room was very positive and people were talking a lot about their first computers there. However, the biggest surprise for me is that the joystick survived all the players. Some of them gave it a hard time.

Atari XL Design

  • by

I like the clear aesthetic of the Atari XL series. These were the most visually appealing 8-bit home computers from the 80s. It’s sad that the design of newer Atari computers was much worse after Jack Tramiel came to the company.

Atari XEP80 (1987)

  • by

This device allowed users of Atari 8-bit computers to display full 80 characters per row on their screens. XEP80 came too late and used very strange way for connection with the computer – it was attached to a joystick port. It was quite slow with the original driver but there were 3rd-party drivers allowing users to double the screen update speed (matching 9600-baud serial terminals).

It’s a shame that Atari came with the device at the end of the 8-bit Atari series life and implemented it this way. The powerful terminal processor inside could do much more but that would need to connect it using the bus expansion connector. However, that connector changed over time on the 8-bit Atari series so that would affect compatibility. As a result there were not many software packages supporting its 80×24 mode.

Unfortunately, I didn’t have much time to play with the device. I only run bundled demo programs and took these photos (don’t be confused with the Commodore monitor and keyboard). I will definitely take it home one day and try how seriously this could be used back then.

SAPI-1 (1983)

  • by

On the left side, you can see SAPI-1 – a professional computer that was made in the Czechoslovak Socialist Republic and was used mainly for industrial applications. Its architecture was modular and not very far from S100-bus computers. One of the cards contained CPU (Zilog Z80 in this case) while other cards contained RAM, ROM and communication interfaces. It was able to run CP/M which was loaded from 8-inch floppy drives.

This photo is from the last Bytefest show a few weeks ago. We were copying files over a null-modem cable from Amstrad CPC6128. File transfers between different CP/M computers were not an easy task back in the 80s. Each computer had different floppy drives or at least a different logical format of the disks. This was very similar to terminal incompatibilities where every full-screen program had to support tens of terminals in order to be compatible with most CP/M computers. If your computer was not on the list, you ended up with incorrect layout of the text on the screen.

Because of these incompatibilities, serial and modem connections were the best ways to transfer files back then and they are even today. Don’t expect something “plug and play”. Although I could set the transfer speed in software on Amstrad CPC6128, the owner of the SAPI-1 had to remove the communication card and change the serial link configuration using a soldering gun. Another issue was to find programs with compatible transfer protocols but that’s a different story. Finally, after less than an hour, we were able to copy all our precious files.