3 ms·

Can anyone ELI5 this passage: However, the 205 drum was more sophisticated. It was divided into two areas. The primary storage was 80 words of 0.85 millisecond

Can anyone ELI5 this passage: However, the 205 drum was more sophisticated. It was divided into two areas. The primary storage was 80 words of 0.85 millisecond average access memory. The secondary storage was 4000 words of 8.5 millisecond average access memory. The fast memory was accomplished by placing the read-head one tenth of the way around the drum from the write head. Thus anything that was written was available one tenth of a rotation later. I’m confused how the mechanism as described could be considered “fast storage”. What if the word I want to read isn’t the one I wrote a tenth of a rotation ago? Was there some kind of refresh scheme involved so the same 80 words were rewritten ten times along each rotation? But if you could keep track of 80 words you wanted to write periodically, you wouldn’t need to...

SonOfLilit 6y ago
I'm guessing the write head copied the read head unless instructed to write a new thing at that address, so you didn't need to keep track separately. Algorithms (implemented in parallel with electronics): Secondary storage algorithms: Read(addr): While address != addr: nop Return read_head_value Write(addr, data): While address != addr: nop Write data Fast storage: Read(addr): While address % 10 != addr: nop Return read_head_data Write(addr, data): While address % 10 != addr: Write read_head_data Write data
- rst 6y ago
  That's it. See description on page 3 of the manual: http://bitsavers.org/pdf/burroughs/electrodata/205/3021_B205_Central_Computer_Hbk_Mar56.pdf http://bitsavers.org/pdf/burroughs/electrodata/205/3021_B205...
  - Stratoscope 6y ago
    That manual is great! I highly recommend reading through it for anyone interested in computing history - and anyone interested in how to communicate clearly in technical writing. Here's a fun report from someone who had the 205 as their first personal computer: https://blogs.mathworks.com/cleve/2017/10/09/my-first-computer-the-burroughs-205-datatron/ https://blogs.mathworks.com/cleve/2017/10/09/my-first-comput... I loved this story at the end: > Skip on Minus > One of the programs that I wrote during the summer at the University of Utah involved a loop that was exactly 20 instructions long. That meant the entire loop could be loaded into the high speed memory. It didn't even need the jump instruction from the end of the loop back to the beginning. It would just continue execution from the duplicate of the code in the next block on the drum. The trouble was there was no way to exit the loop. > I needed a "Skip on Minus" instruction. There was a "Skip on Plus", but no "Skip on Minus". The EE grad student who maintained the machine was a guy named Joe. I wish I could remember his last name. Anyway, I told him I needed a "Skip on Minus" instruction. He said, "I'll put one in". He disappeared behind the cabinets with circuit diagrams and a soldering iron. He called out, "the op code will be 51". > I wrote my program with a "51" instruction. It worked perfectly. And so the University of Utah had the only Burroughs 205 Datatron in the world with a "Skip on Minus" instruction.
Taniwha 6y ago
This is head-per-track drum/disk (none of this new fangled seeking stuff) - probably the slow tracks has a single set of R/W heads per track while the fast tracks had multiple heads spaced around the drum. When I was a B6700 systems hack, mid 70s, we still had head-per-track disks for system files (and paging/swapping) and slower seeking (removeable) disk packs for system files

SonOfLilit 6y ago

I'm guessing the write head copied the read head unless instructed to write a new thing at that address, so you didn't need to keep track separately. Algorithms (implemented in parallel with electronics): Secondary storage algorithms: Read(addr): While address != addr: nop Return read_head_value Write(addr, data): While address != addr: nop Write data Fast storage: Read(addr): While address % 10 != addr: nop Return read_head_data Write(addr, data): While address % 10 != addr: Write read_head_data Write data

rst 6y ago
That's it. See description on page 3 of the manual: http://bitsavers.org/pdf/burroughs/electrodata/205/3021_B205_Central_Computer_Hbk_Mar56.pdf http://bitsavers.org/pdf/burroughs/electrodata/205/3021_B205...
- Stratoscope 6y ago
  That manual is great! I highly recommend reading through it for anyone interested in computing history - and anyone interested in how to communicate clearly in technical writing. Here's a fun report from someone who had the 205 as their first personal computer: https://blogs.mathworks.com/cleve/2017/10/09/my-first-computer-the-burroughs-205-datatron/ https://blogs.mathworks.com/cleve/2017/10/09/my-first-comput... I loved this story at the end: > Skip on Minus > One of the programs that I wrote during the summer at the University of Utah involved a loop that was exactly 20 instructions long. That meant the entire loop could be loaded into the high speed memory. It didn't even need the jump instruction from the end of the loop back to the beginning. It would just continue execution from the duplicate of the code in the next block on the drum. The trouble was there was no way to exit the loop. > I needed a "Skip on Minus" instruction. There was a "Skip on Plus", but no "Skip on Minus". The EE grad student who maintained the machine was a guy named Joe. I wish I could remember his last name. Anyway, I told him I needed a "Skip on Minus" instruction. He said, "I'll put one in". He disappeared behind the cabinets with circuit diagrams and a soldering iron. He called out, "the op code will be 51". > I wrote my program with a "51" instruction. It worked perfectly. And so the University of Utah had the only Burroughs 205 Datatron in the world with a "Skip on Minus" instruction.

Taniwha 6y ago

This is head-per-track drum/disk (none of this new fangled seeking stuff) - probably the slow tracks has a single set of R/W heads per track while the fast tracks had multiple heads spaced around the drum. When I was a B6700 systems hack, mid 70s, we still had head-per-track disks for system files (and paging/swapping) and slower seeking (removeable) disk packs for system files