When Memory Devices Get TOO Small

I bought a used (barely) Svbony SC311 astrocamera. These are cameras made only for astrophotography.  They are very light and can talk directly to your phone so you can adjust settings on the fly and record (I think) directly to your phone via WiFi. In any case, it will record to the microSD card that goes in the slot. But seems not to have stayed in the slot when I picked the SC311 off the desk where it was charging and walked to the easy chair where Rosie insists on sitting on my lap. I am not blaming this very loving dog. I believe I lost the microSD card before I reached the chair. 

These cards are tiny. I still do not see it on the floor anywhere. Amazon is promising delivery of a larger one tomorrow, 128GB, not physically larger.

Disappointing Discovery

 My plan to machine this adapter from a 6"x6"x1/2" sheet of aluminum ran into some size issues. The 6" chuck cannot hold that big a workpiece. Nor does my mill have enough Y capacity to center and drill the middle of the plate. 

Okay, cut it down to 5" x 5" and it should work. My chop saw cannot hold down that size of sheet horizontally to do that cut. Vertically, it has insufficient capacity. I regret giving up bandsaw. At least I have roomto put one in the shop.

I Was Putting Away Emergency Rations in the Garage

Canned chili and rice and emergency rations followed me in.

I doubt that I have the stomach to dress a deer, especially because Rhonda would adopt it.

As she walked across the lawn, our wolfette pack lost their minds.

My First Multitasking Operating System (Back to the Disco Era, Yeah; Really Groovy)

This is a slightly refreshed discussion from 2018. I started thinking about MINITS and sleep became impossible.

I have mentioned learning to program on an IBM 1401.  This computer processed class scheduling, attendance records, and grades for the entire Santa Monica Unified School District.  I used my knowledge and access to get myself moved from one section of German to the other because the girl that I was obsessed with was going to be in that section.  Another one of the computer lab rats, Curt, claimed no knowledge of how he had dozens of unexcused absences from P.E. and still received an A.

Anyway, the data processing coordinator for the district somehow rescued a computer pound puppy.  It was an odd dual minicomputer system named MINITS (for Miniature Time Sharing System).  It used two Interdata minicomputers, a Model 3 and Model 4, sharing a common 32K RAM space. A model 4:

The dials on the left and the push buttons at bottom allowed you to enter data into various memory locations, such as when you needed to put the boot code in to load the OS from the drum.  This was a slow process.  One friend, Curt, demonstrated his ability to enter the boot sequence accurately with his toes.

  I do not know if the Model 15 was an Interdata supported product, or something Cerf's team created. The Model 3 was for control of the teletype terminals and modems. The model 4 did the timesharing processing.

This is a model 33 teletype.  It printed and accepted keyboard input at 10 characters per second (we finally managed to find a 30 character per seconds modem and CRT to attach).

Modems were the way you communicated with a remote computer well into the 1980s. (I still remember the thrill of installing a Telebit Trailblazer modem at work and getting 14,400 bits/seconds.) It had an acoustic coupler: two rubber orifices into which the handset fit. The modem (modulator/demodulator) took ASCII electrical bytes, converted them to a variety of interesting sounds and sent them over the phone line. At the far end, another modem converted those sounds back to ASCII bytes. It was, as you might expect, less than perfect. Line noise could garble the characters. This is why teletypes operated in either full duplex or half duplex mode. Full duplex mode: you typed a character. The far end echoed it back so you knew what character it heard. Half duplex: the character you typed appeared immediately. 

An early minicomputer editor was called TECO. It was said that TECO commands were hard to distinguish from line noise.

Yes that is a paper tape punch and reader on the left side, which used this stuff:

There are indeed more than 8 rows.  One is a parity bit, and the other is some other out of band signaling information that I have forgotten.  Slow!  I once did a three pass assemble* of the Interdata Model 4 OS from paper tape as my first summer job after graduating.  (That was 12 hours of profound boredom, fixing paper tape jams and tears.  Why three passes?  No hard disk to store intermediate results, like symbol tables)

Anyway back to MINITS.  This was one of Vint Cerf's brainchildren.  The idea was a relatively cheap timesharing system.  We had scads of listings for the operating system, BASIC interpreter, and some of the utilities and games, printed out on a drum printer that was attached to the Univac 1108, that was supposed to be the mainframe to which this would be attached. 

A drum printer was one of two mainframe printers of the era. Chain printers, like the IBM 1403:

An early line printer that used type slugs linked together in a chain as its printing mechanism. The chain spun horizontally around a set of hammers. When the desired character was in front of the selected print column, the corresponding hammer hit the paper into the ribbon and onto the character in the chain. Chain and train printers gave way to band printers in the early 1980s. 

If this sounds incredibly slow: it was not. An IBM 1403 chain printer:

The original model can print 600 lines of text per minute and can skip blank lines at up to 75 inches per second (190 cm/s), while the model 3 can print at up to 1400 lines per minute. The standard model has 120 print positions. An additional 12 positions are available as an option. A print chain with up to 15 copies of the character set spins horizontally in front of the ribbon and paper. Hammers strike the paper from behind at exactly the right moment to print a character as it goes by. In later models, the print chain is replaced by a print train; print slugs instead of being mounted on a chain are placed in a track.

Drum printers used a series of type slugs mounted on a drum. A print stroke would line up the appropriate slug for each letter (perhaps all the slugs for the entire line to be printed?) and stamp them through a ribbon onto that same distinctive wide fanfold paper used by chain printers:

Because alignment of the type to the line was happening at very high speeds, the letters would often being not exactly centered in the line. You would see characters printed perhaps a few hundredths of an inch off a perfect impression vertically. I suspect this could be adjusted for better output accuracy but the listings we had in binders were all suffering this drunken vertical print alignment.

The MINITS hardware was unique. It had a large magnetic drum that did two things: every few milliseconds as the drive reached its zero track position, it generates an interrupt that told the operating system, "It is time to give another user some time."  (Clock generated interrupts?  Not sure when these appeared on other minicomputers.)  Also when it came time to swap users, the entire user context (the current contents of his BASIC program or whatever else a user was running, which I believe went from X'5800' to X'8000') would be written to the drum.  The OS would then load the next user's context and give him execution time.

How much time?  The OS had a concept of Terminal Control Block, which specified how many milliseconds he was allowed and the priority of his terminal's task.  By adjusting these numbers on the fly, you could annoy the heck out of a remote user.  (Imagine typing a key on the teletype and waiting a second or two for the echo to print on the paper.)  There was one in the math lab several thousand feet away, and another attached by 110 baud modem at Lincoln Junior High, some miles away.  We also borrowed a teletype to take home on weekends, for breaking into ARPAnet; more about that some other day.) When there were problems, either because someone was manipulating the remote user's TCB or because of hardware problems, the long-suffering, but always polite Lincoln math teacher responsible for this learning project, Mr. Winkenhower, would call us to find out why he was not having any luck. 

Anyway, I learned a lot about how operating systems worked in 11th and 12th grades.  The Control-V key would drop you into a debugger where you could by accident do enormous damage requiring a hard reset, including re-entering the boot sequence through the front panel.  The right set of common keystrokes would change RAM in areas that were lethal to the OS.  It was needed, however, to fix some problems on occasion so we could not just disable it.  A fellow student, Curt, and I wrote a utility in Interdata assembly language and then hand compiled it (we had no assembler program) that would do all the  necessary functions but otherwise block access to the debugger.*

I also learned how to redirect the illegal instruction interrupt, which would drop you into the debugger.  At some point I decided to be clever and build an illegal instruction driver that would recognize instructions that were part of the Interdata Model 70 instruction set. These were short relative jumps (branch within 256 bytes so the instruction only took two bytes instead of four) and add, subtract, multiply, and divide instructions (limited to I think 8 bit values; AHM (add halfword memory AHM register, value) and it would simulate these perfectly.  Then I foolishly started adding these instructions into the OS.  It came to a near complete standstill as basic OS functions would keep running through the illegal instruction ISR.

*Computers execute instructions stored in RAM as binary numbers usually expressed in hexadecimal.  X'5A' was the Interdata AHM (Add Halfword to Memory) instruction.  (I remember because they used many of IBM 360 mnemonics and architecture; 16 general registers all of which except 0 could be index registers; and where X'5A', was a 32 bit add of memory to register on the 360, X'5A' was AHM 16-bit add of memory to register on the Interdata),   It not being very easy for most people to remember all the numbers, we generally wrote in assembler language.  AHM 5,VALUE would add the 16 bits at symbol VALUE to register 5.  The program that converted these easy to remember mnemonics into binary was called an assembler.

Ultimate Jury-Rigging

I am trying to get my WiFi adapter out of the Faraday cage that is my shop. This gives me 45 Mbps. Unfortunately it is not stable.  It uses two USB 3.0 cables end to end. I need some height to get line of sight to my range extender.  Unfortunately,  antenna masts like we used to use for televisions in the ancient times are hard to find now. Pipe would work but I cannot get an 8' section in my car. Suggestions?

What is That Tool For?

I found an odd T-handle tool while organizing my shop.

What is that for? I got the 6" Sears 4 jaw chuck out and suddenly it all made sense:

Unfortunately,  "6 inch" chuck is the diameter of the body not size of workpiece it can hold. It looks like a 4.25" workpiece would fit.I may have to center drill and tap the 3/4-16 hole for this in the drill press, a far less precise process. 

More Evidence That Trump's Failure to Plan for Closure of the Strait Sank Us

Vance is admitting that the war and rising prices lost us the election. In some logical way, ending Iran's nuclear ambitions should take precedence over short-term financial pain.

Voter are often not logical. High prices are pain right now. A nuke going off in a freighter in an American harbor is a possibility some years from now. That former leftist and present "conservative" Tucker Carlson has been pushing the Israel First explanation of American foreign policy probably played into this effectively.  That stopping the nation that calls us the Great Satan is an America First policy may not seem obvious to voters born after 1979.

It does not help that Republican candidates often sounded tone-deaf like  11/4/26 Time:

Hitefield adds that Hyde-Smith had some “gaffes” during the campaign, when she made some remarks about the rising cost of living that some voters felt were dismissive. For instance, when asked about soaring costs, including beef prices, during an interview with WLOX in February, Hyde-Smith applauded the passing of Trump’s One Big Beautiful Bill and went on to say, “It is on everybody’s mind. It is certainly me at my house. And you know, you have so many proteins to choose from. And all commodities go through peaks and valleys.”