Clock update and Hodge podge

Day 27

     In case you have not looked over the contents of the Google drive folder I posted here is the clock circuit diagram. Looking it over in this form as opposed to in any of the HP drawings seems a bit more sensible to me. Most likely due to my having drawn it out. Operation of the single step is becoming more clear now and the overall function is starting to take shape in my head. This bodes well for when the circuit is built as it will likely reveal what is left for me to find in it.


      Looking over the HP computer papers 1 theme is always present, control is up to you to figure out and while I intend to do just that the RC2 design shows many of these control mechanisms plainly. In the full adder of the ALU's the logical function of the increment function is described but not shown the RC2 goes into full detail as to how this is accomplished. As an amendment to my post from 27 Feb the logic block of the RC2 is much less robust that the HP computer as it can only AND, and NOT while the HP computer adds OR and XOR this is a severe speed limitation as OR and XOR are important functions however it only pays a speed penalty as with the AND and NOT you essentially have a NAND gate and NAND can be chained to create any of the other functions, so the ONLY penalty is speed. Speed is a penalty that can be paid easily with the RC2 as so many of it's other features add so much more speed to the system this also has the added benefit of reducing the number of enable circuits in the computer which while not much of a reduction in parts is still something to consider. More differential notes on the RC2 show that a single relay clock circuit was used instead of the larger but more stable HP clock. The finite state machine in each appears to be capable of 24 steps though the reset circuitry is different and the RC2 uses a 12 count with a prime count for each step more will come on that soon though as I believe the finite state machine will be the next prototype I build after the clock and at least 1 bit of the ALU, time will tell.

     One thing I am starting to see is that while these 2 computers are drastically different, these differences mask the overwhelming number of similarities. Both authors are extremely competent and very efficient and I think that explains why even the differences are similar in many ways, I intend to leverage this as the HP papers show little of the control circuitry but the RC2 shows much of it but glosses over the more in depth explanations of the functional bits. Combining these 2 works and modifying things here and there will allow for potentially the efficient and true design I desire.

A further note on parts this week I ordered my second shipment of relays as well as the capacitors for the clock, 50 switches, and 20 indicator LED's this puts me in a good place for prototyping once they all arrive within a few weeks. These orders with the first batch which I'm still anxiously awaiting will allow for up to the full ALU and clock to be built and possibly the finite state machine.

RC2 ALU

Day 25

     The Largest departure between the HP and RC2 computers is definitely in the ALU itself the RC2 has a much larger instruction set and can carry out several more base functions as such this all adds to the overall complexity of the design but also helps to drastically improve functionality. What the HP can complete in a dozen clock cycles the RC2 can complete in 6 or fewer depending on the particular functions. This example is a perfect showcase for the evolution of modern computing and Moore's law in action using more modern techniques and customized components not only did the speed increase greatly but so did the complexity and usability.

      The HP computer ALU consists of a full adder a logic block an incrementer and a left shift register but not much else. The RC2 has all the same functions but can carry out functions such as NOT or SHIFT on both registers not just 1 also the SHIFT functions go either right or left which drastically reduces cycle count in the case of a RIGHT SHIFT. The SHIFT can also be manually selected between circular or non-circular shifts. The RC2 also features a CONSTANT function that as of yet I have not seen in the HP computer but would drastically assist with reducing cycles and memory accessing.

     I intend to spend some time studying the texts on both more in depth tomorrow and ferreting out more of the differences and to see what if any modifications I may wish to start designing into my build. Monday, however, I intend to move back to the clock circuit and walk through its operation with the schematic I drew up. Wednesday we will return to the RC2 build and what we can learn from it. 

Schematics

Big news I finally finished the first of the schematics involved. I have setup a google drive folder with  the .fzz file and screen cap of the schematic I will be adding more soon but the Clock circuit is up and having worked it out on Fritzing has helped immensely with my understanding of things.  As soon as the first shipment of relays arrives this will definitely be the first prototype circuit that gets built many pics to come with that also. Many more to come soon. The game plan with these schematics will be to begin by drawing out the schematics provided in Harry's literature and other materials after that it will be left for me to modify each section as needed the various component parts will have interconnect diagrams drawn up then an overall block diagram will be built to guide the actual final assembly when the time arrives. This folder will also house all of the still shots of the build as it goes any videos will be posted to youtube.

RC2 returns for a comparison.

Day 22

     Today we will be looking at the ALU in some depth but with a focus on the differences between the ALU logic in Harry porters computer and the Relay Computer Two. On the surface they have many similarities however the differences begin with component selection Harry uses a 12V ice cube type 4PDT relays while RC2 uses both 4PDT and SPDT relays with  much lower power capability. While this is a small difference it is the first of many that allow for a much smaller, faster and more robust CPU, however it comes at the cost of needing much more in the way of support materials and memory. while this is a better representation of a modern CPU it does little to showcase the beautiful simplicity of the original designs of the 40's, though, that is not the purpose with RC2. In the case of the Harry Porter computer or my own the focus is instead on the theory and functional operation without thought given to speed or complexity but instead to understandability.

     I am going to spend some time breaking down these differences as I see them and where they each have strength and weakness. To start with the ALU itself. First looking at the registers instead of using a pair of NOT gates to time out the delay between the LOAD and SELECT commands allowing for the HOLD line to be powered or cleared as needed RC2 uses a single SPDT relay and a 10uF capacitor to do a similar job given the power needs of the smaller relays this is potentially more effective and definitely more simplistic. However, it comes with the disadvantage of time in the larger relays of the HP computer as these relays consume more power even if at a lower voltage therefore this design lacks scalability while the HP design will work for even the smaller components.

A word on my comparison, I think both of these computers are utterly fascinating Harry's computer is a great teaching and demonstration aid and showcases the old school power that computers had while the RC2 shows just how complex and amazingly fast they are capable of being. so throughout this comparison do not get the impression that I don't appreciate the RC2 or think it inferior. It is just different and not the direction I am going. The RC2 is amazing and the goal of loading windows with it is quite lofty and rather neat and I'm intrigued and will be reading much more extensively on it but it is not quite my goal so don't judge it or me to harshly on that.

Functional Operation

Day 20

     Today I finally got some work going on Fritzing and hope to have those files to share later this week and between that and the anticipated arrival of the first shipments of relays should be able to get back to work on the details of the clock circuit. For today, though, I will be focusing not on any specific circuit but on the operation of the overall system as I understand it to this point.

     The overall function of this computer starts with a program being inputted  by hand byte by byte via the 8 bit data bus. At the same time an address is assigned to the instruction being entered on the 16 bit address bus. once the program is entered into memory the initial value can be loaded onto registers as needed and then the clock circuit is unfrozen and the program is allowed to run in sequence until either a halt function is called or the clock circuit is refrozen. Arithmetic functions are loaded onto the B and C registers the result of this function is loaded back onto the data bus and inputted to whichever register needs it next then the increment register will signal to load the next instruction which will repeat the process. There are several registers on besides the B and C registers each has a specific function which almost all involve storage for a time for 1 reason or another. Registers such as the M1 and M2 or J1 and J2 or X and Y registers can also access the 16 bit address bus and in the case of M and XY they can load data onto the data bus as well J can only read from the data bus there is an incrementing circuit feeding into the Program counter solely for the purpose of advancing the program instruction set. While there are several other details such as control lines they add little to the discussion of the overall function of the computer. 

     Wednesday we will be going into more depth with the function of the ALU even more so than before and with any luck schematics will be forthcoming as well.

      As a note on the Fritzing work I am still looking into building a set of custom parts but for the moment I have decided to go with individual discreet components. This will work in the short term for getting schematics drawn up and shared and will be refined as time goes on. So for the now my relays are made up of a coil and 4 SPDT switches simply laid out to resemble a relay of the type I desire which will work quite well for schematic visualization but will not allow us to leverage the full power of the Fritzing platform though for a project of this scale I suppose AutoCAD would be better suited for the rest of the layout types. If you haven't used Fritzing for a smaller project I highly recommend it as it will allow you to take a breadboard project and pull a schematic and PCB layout out of it with minimal work or take a schematic and prototype it well. It is a powerful tool that is free and rather well built.

Not Quite The Clock Circuit As I Had Planned

Day 18

     This was supposed to be an in depth look into the clock circuit but I'm reading through the material and looking over the schematics and redrawing them myself and I'm just not seeing it yet hopefully later this week I can come back to it when the relays arrive and I can build it and see it in action.  This actually seems to be a problem I will be running into a lot with the hand drawn schematic photos Harry supplies on the website. I am trying to hand redraw them into a form factor more to my thinking but would prefer to get them up on Fritzing asap so I can look them over in greater detail. I also think all of these circuits will be better understood oncee they are broken down and built in the physical realm.

     Problems with my sleep deprived brain aside, on the physical layout of the cabinets. Harry's design is constructed of 4 cabinets I intend to split off the Memory module to its own cabinet to allow for further expansion of the computer but more to give space to a less modern and more period appropriate form of memory in the future as well this major modification will be baked into my design but will be performed as an upgrade not part of the initial build. I am also considering adding a permanent storage form to store whole programs but that will be a considerable add on in the future but will greatly add to the functionality of the overall system.

     Well today's post was something of a softball but I promise back to the salt mines on Monday where hopefully I can get back to the clock otherwise we'll be on to the next part.

The clock circuit (Basics)

Day 15

     Shipping notification has been sent on 10 of the relays I have on order hopefully I will have them in hand within a week and a half. Just in time for the next order to be placed, hopefully the other set arrives by then as well so I can make a full decision as to which supplier to use. 

     At the outset the clock looked to be 1 of the simplest sections of this build having now delved into many of the various pieces and seeing how the clock will need to behave I have the feeling this is a much bigger portion than first glance will tell.  The basics of the clock is a simple recursive chain of 4 relays with capacitors in between to add a slight delay and allow the clock to pulse fully at any given moment 2 of the relays are on and as such we can derive a square wave using a simple Boolean expression. The big trouble comes in when you understand that this clock needs to be started and stopped in such a way as to not give errant pulses and also needs to be able to be single stepped through it's various states this adds a level of complexity not initially seen.  I think this will be broken up into several days of chasing down answers.

     For today we will focus on the 4 main relays and their capacitors The 4 relays are labeled "A" "B" "C" and "D" each coil is attached to the capacitor and the normally open contact on 1 of the prior relay's switches A to D, B to A, C to B, and D to C the common contact of that switch is connected to the normally closed contact of a different switch on the prior relay, the common of which is connected to voltage. This means that once the circuit is set to running it will continue to run indefinitely without any assistance from us. However it also means we cannot control it without using some control circuitry. Which we will begin to breakdown in Saturdays post. 

     On the physical end this basic clock has only 8 schematic parts which are actually made up of 24 discreet parts the 500uF capacitors used are actually 5 100uF caps wired in parallel the part Harry uses is a non polarized style and is the exact piece I intend to use as well.  It is from www.allelectronics.com part number is NC-100.  I intend to list in a separate post in the future what and where I sourced all parts from so they can be easily found from a single page but I will also continue to discuss them in their related posts. 

Register Storage

Day 13

     I am having a lot of fun getting lost in the minutia of this build and there are a lot of little nuances to it to get lost in but the real story is how all of this relates to the architecture of modern computing. While the components have changed, shrunk, and sped up significantly the basic functions of those components has not changed. The transistors on a modern CPU act in the same way as these relays except they switch much faster and with much lower voltage and current. These similarities get to the heart of why I'm undertaking this little adventure, I have long been a lover and user of computers and electronics now it is time to fully understand what is going on with them. The hope is to become not just another brick in the consumer wall but to be an active participant of the culture I have loved for decades.

     We've already looked at the shift register now let's look at the storage register the basics of it is a simple latch circuit where only 1 switch of the relay is used and the common of that switch and 1 side of the coil are connected the N/O contact is connected to a "Hold Line" that allows bits loaded to be stored as long as the hold line is powered. this memory buffer is easily cleared by just dropping power to the hold line. At that point the only relays that will stay active are the high bits on the bus but if the bus should change it's value then so will the high bits in the register until the hold line is activated again then any high bits will remain high even if the bus changes state.  The problem comes in when the bus changes high bits will stay high but low bits that go high will then latch high as well to prevent this we use the same type of enable circuit from the ALU to either allow or disallow the bus contents to be loaded onto the register. 

     To allow the register to be loaded from the bus or to load onto the bus we will use 2 control lines and 2 NOT gates the control lines are LOAD and SELECT and they are connected together by the 2 NOT gates as well as the register the select line is connected to the enable circuit's control line and to 1 NOT gate the other side of the NOT is connected to the other NOT and the HOLD line of the register itself the other side of the second NOT is connected to the LOAD line. This simple setup gives us the clear function before any loading of the register from the bus and allow us to write to the bus as well. As listed this circuit will create a feedback loop in the Hold line which would destroy our data so instead of using a single NOT on the LOAD line we use a split NOT separating out the NOT function to 1 switch and the Hold line to another both powered by the same common this prevents the feedback of any high bits from causing oscillations in the Hold line control.

     Next I believe we are going to skip to the clock circuit to get an in depth look at it's function and what impact it has on all of the things we've done so far. At the end of the day the clock is important as without it we would be hand advancing this computer and that would reduce the automation effect of it. not to mention all the tedium it would entail. 

Doodling and buying

Day 11

     Yesterday I ordered the first sets of relays Relay 1 and Relay 2 I am trying both as Relay 1 is almost certainly the right relay that I want but relay 2 is $0.21 cheaper and in a larger lot sale which may allow for an even further reduced per unit price. My only worry is that relay 2 is not the correct part as it seems it may also have the terminal base which would make prototyping and testing much easier, we shall see in a few weeks when they all arrive. With 30 relays on order the game plan is to start building some test rigs and proof of concepts first in line will be a limited function of the adder and function output of the ALU and/or perhaps a clock circuit.

     I have also spent a fair amount of time looking into building out these schematics on Fritzing and have hit a bit of a wall with my inability to use illustrator or a similar program but am working on it. Instead I have been hand drawing the circuits I have discussed here to get a more tactile feel for them and how they will connect to the overall design. Pictures of this work as well as custom Fritzing part files to come.

ALU Logic Breakdown Part 2

Day 8

     Ok we left off having given a very dry basic description of nearly all of the ALU functions I don't foresee myself adding a whole lot to this area as it is very compact essentially being just 4-6 relays per bit and there is little I can add to the function of the system itself excluding perhaps adding new functionality. This may be a project in and of itself so if I do tackle it it will be after I have built and deployed this computer then and only then will I start adding things to it. The only part of the ALU itself not yet mentioned is the left shift circuit which like all the others is always done but only read when necessary. The left shift is a simple function of shifting each wire 1 position to the left and the leftmost wire wraps around to the rightmost bit position. with this function we can recurse the function multiple times to cycle through all states of left or right shift, this wrap around function makes the shift a circular left shift. The advantage here is we can keep the instruction set simple with only a single shift instruction that we simply need repeat a number of times to allow for any amount or direction of shift(once for a single left shift 7 times for a single right shift and so on. With all of the functions occurring simultaneously we need only control which state gets fed onto the bus as our result this is accomplished with several enable circuits these are simply 2 relays that accept the enable signal on the coil closing the switches and allowing the result to flow onto the bus.  There is also included in the ALU a zero detect circuit that reads the result bus and indicates if a zero response is given. Also present is the sign bit on the bus which is read from the most significant bit a 1 indicates a negative number a 0 a positive this is simply read directly from the bus with no extra parts. Obviously this is only a basic overview of the papers given for the Harry Porter computer and his information goes into much more detail but is also full of theory that I already have a solid grasp on so I've boiled it down to the descriptions and the functions I see as necessary and/or difficult for me to personally understand. 

     On the enable circuits they are fed their states from a 3 to 8 decoder that converts the function operation from a 3 bit binary number to an 8 bit enable output thus allowing only 1 of the ALU's functions to be carried out easily and reliably . There are in fact only 7 functions the ALU can carry out at the moment which would appear to leave room for another function later to be added should any single function be advisable when in fact the not used function is necessary for incrementing steps where other information is flowing over the data bus.  If more functions are desired a 4 to16 or larger decoder will be required adding great complexity but with the benefit of greater usability. This is in fact a direction I am very much considering going after initial build and testing is complete. 

     In the coming days I will try and draw up a complete ALU as I have studied it just to get a feel for it's build. Next will be the registers a crude but fascinating form of memory storage which will likely lead to the first prototype builds I intend to attempt in a few weeks. My first prototyping build will be a 2 or 3 bit version of the ALU with registers and led indicators. I will also be taking some time to revisit the Relay Computer 2 ALU and register just to see if that makes more sense now that I've got some basic learnin under my belt. 

ALU logic breakdown part 1

Day 6

     The ALU is a combination of an adder/incrementer, left shift, and several Boolean logic functions. All of the possible functions are carried out simultaneously regardless of need and only the result that is desired is loaded onto the bus. This means that all of the logic functions can be carried out on just 2 relays per bit giving us the 4 outputs of the AND, OR, XOR, and NOT functions. The NOT function is carried out only on the B input but all others are carried out on the B&C inputs.  the adder/incrementer is also made up of only 2 relays and gives us a full adder with a dual rail carry in/out bit. The dual in/out carry bit allows for negation of the sum allowing the computer to work in negative numbers gives a vast improvement in flexibility. The add circuit can also be used by simply inputting a 1 to the carry line on the B input alone to increment should a simple count up be necessary. More to come Wednesday.

Beginning the breakdown

Day 5

Today I'm going to begin a focus on specific parts of the computer and my thoughts on how it works and what my build will need along with just general thoughts on things. 

The Cabinets

     Each of the cabinets in the Harry Porter computer are 26" x 38" and framed in Mahogany, this is fairly robust and quite pretty though I do believe I will go with either a different type of wood or possibly another material altogether the backs are constructed of  melamine with an acrylic front plate for ease of inspection I may go with acrylic on both sides. The front and back panel are slid into a groove routed around the boards of the frame and the relays and all components are affixed to the front acrylic which is sectioned for ease of handling. A part of me would like to mount an extra piece in the center of the to only hold the components then hinge the front acrylic and allow only the switches and gear necessary come to its level, time will tell if this instinct is correct or nuts but I believe it would allow greater freedom for maintenance and cleaning tasks. the boards are slid in through the top which is then screwed down and this I know can be easily improved with a hinge and clasp system. Butt splices are mentioned as the method of combining the various modules but I believe terminal boards would be a neater method. I understand the additional failure points these will introduce but the increased readability of where everything is going will likely greatly outweigh the reduced reliability. Terminal strips are used extensively in the equipment I work on every day and they rarely give issue unless someone has been dinking around with them, and many of them have been running for 20+ years and through several moves with no issue plus they have dozens of motors and bearings and belts rattling things constantly. The other option would be to use a molex type connector between modules with a backbone wiring harness running where needed. I think some combination of the 2 will be the final answer as these all work well together. In the end and for neatness sake I will be trying to avoid butt connectors and splicing wherever possible though I know at times it will be unavoidable but this seems to be the biggest gain I can make to not only improve the robustness but the maintenance ease of this beast of a machine.

     I think that's about all I can cover for today Monday we'll finish up the case designs and talk about the parts list. Then from there I'm thinking the ALU.
    

Finally some understanding and a plan starts to take shape.

Day 4

     Program note I mentioned in my first post a desire to stick to a schedule and so far I've not really bothered thinking about it but starting Saturday which is day 5 I will be sticking to that schedule of 3 posts per week Monday, Wednesday, and Saturday I am doing this for a few simple reasons. First it keeps me working on this project consistently, but not overwhelmingly so. Also this keeps things on a schedule so on the chance someone follows along with me they know when to expect things coming down the line.

     Finally I have stopped chasing my own tail and gone where I knew I should have gone in the beginning. Harry Porter The first half of the video tutorial has really helped clear things up as he walks you through the building of each of these circuits I won't bother repeating it all as it's a boatload of info delivered very well and I don't want to mess it up. If interested go download it and watch it for yourself he does a great job of explaining it. I think I'm going to watch this a few times through to get as many of the details in my head as I can. My only true disappointment so far is that he uses modern silicone for the memory though he's not without good reason for it looking at the number of relays required to build in 32K of memory. It is quite prohibitive so this is the direction I will likely go as well if for no other reason than I haven't got an entire room to fill with banks of relays for this project let alone the cost.

     On costs wire in bulk is cheap as are the LED indicators used throughout this design but the 4PDT relays are going to be rather costly and if I clone Harry's computer I will need 416 of them I'm planning to buy 425 total to have spares and for various other potential projects I'm thinking of buying these in 25 piece lots so as to not break the bank. Which given my pay cycle of every 2 weeks should get me all of the relays I need by the end of September so the plan now is to do final assembly and operation by mid October. This seems like a reasonable plan to me as I won't be over taxing my budget but will be able to keep things fresh and moving along at a steady pace. I hope to be deconstructing and building programs for the bulk of that time so I have a lot of great stuff to play with when it's finished.

     Looking at things and exploring the various relay computers I have seen in the past few days I am certain that this is the type of relay computer I want to build. Over the next few months  I intend to break down the design of the Harry Porter computer understand it and where I can make my own practical changes. On a cursory look the majority of those changes seem to be around wire management and things like that plus stylistic changes. I am also considering breaking out the memory module so that I can alter that to full relay use later down the road. My main goals in these tasks are to not just copy what someone else has done but to really break it down and understand how it works and make it my own in some way. Time will tell how or indeed if I can do that. 

     I have spoken to my kids about this project and they are both really excited about the prospects it offers. Plus the cool factor is high even with how geeky it is.

Zusie dead end

Day 2

Well after a decent nights sleep many things have started to coalesce in my brain as to what I read yesterday and I feel pretty psyched for more brain baking today. That said I'm moving my study to a different site with a slightly modernized take on the relay computer here. Just to see what else is out there then tomorrow. I'm going to explore what seems to be the quintessential relay computer which is Harry Porter's relay computer and all of my peripheral exploration points to that being where I can get the most education on the topic. Last night I did some youtube exploring and watched a few videos including Harry Porter's and that is definitely the type I'm going for so that is going to be my guide for the build in all likelihood.

Zusie

Well right out of the gate this seems much less complex mechanically but that is because the ISA and program itself is all stored and run on modern equipment (solid state drive and DOS OS computer) This fact seems to put this into the same category as my PiDP-8 kit cool and retro looking but not truly working in the old way even if the input and/or outputs are the same. The single cabinet it's mounted in looks nice and is more reminiscent of early micro computers than the relay computers I've seen.  though a platform like this may be fun to build for blinking lights type of entertainment. 

About Zusie

moving the 64K memory to solid state seems to solve the same problem described in Relay Computer 2 with program storage and the like. Though they found a traditional workaround to this by using a 16 bit address bus instead of 8 giving the same 64K of memory. The ALU also seems significantly less powerful I'm beginning to see why the RC2 and Porter's computers are multiple panels chock full of relays and this is a single board. It's not bad just not as powerful like a Geo Metro vs a Mustang. They're running the assembler in DOS which I'm sure presents it's own fresh set of nightmares and as such allows the use of lots of parallel cabling instead of standard wire which neatens things up well perhaps I can incorporate the cabling into my design to improve the aesthetic.  Looking into this sadly shows very little of use to my project as all of the instructions are carried by the PC to the ALU for calculation only so very little non modern tech compared to the RC2 or Porter machines though it does provide a potential source for relays. If anyone reads this and knows where they can be found cheap and in bulk by all means let me know. Otherwise if the scrap idea doesn't pan either I think I'll have to start scouring Ebay and Alibaba(probably what I'll research for the rest of the day.

So tomorrow on to the Porter computer and we will be going between that Wikipedia and the RC2 page for the foreseeable future.

Relay computer 2 read through

Day 1 study notes

These may not be well laid out grammatically or even punctuated  at all but they are my notes on what I'm reading and seeing so far. This is just a quickish read through of the text on the Relay Computer 2 page I will be noting the things I intend to study next and my game plan for understanding this particular computer when all of that is finished we will move onto another relay computer and likely another after that then once we've chased all the rabbits we'll begin laying out and prototyping the physical computer. 



The three registers and the ALU

Reading through this the floating zero is pretty straightforward but the first diagram makes little sense to me so far. ISA(instruction set architecture) is mentioned I need to look into that in depth elsewhere and I need a refresher on registers. ISA link Looking at the second diagram the construction of the 8 bit registers seems pretty straightforward if the hold line has power then any bit that gets set will remain set until the hold line is cleared (power removed) the 10 uF cap on the select line gives the momentary hold in power while the load relay switches from select to hold to latch the bits into memory.
And now I'm lost already what the heck is an ALU keep reading hoping to find out but just get more lost I see the various functions this carries out but am not seeing the point yet hopefully it explains otherwise it's yet another research project. OK working out the ALU on Wikkipedia looks like this is where I'm gonna spend a few days of my time the operation seems pretty straightforward but I'm going to link chase this into the ground just to cover my bases. FYI ALU is Arithmetic logic unit so the logical assumption about what that paragraph was talking about is correct I just need to follow this and my other research points before I move on. so this ALU which has all of these full bit adders is waht feeds into the memory registers and thus gives us the flow of data so far I think I'm getting the flow of this shindig but it's still way complicated but really intriguing. I may need to mock a small version of this up on a breadboard just to see it in action.The rest of the ALU seems pretty simple just different versions of the analog Boolean operators I built in high school (Thank you Mr Elwell) though they are pretty neat it reminds me I need to show my son these things in action.

The program counter and memory address registers

This jumps right into some level of confusion about memory but we'll puzzle that out as time goes by it feels like the kind of thing that I'll just pick up through the rest of my studies...time will tell. the half adder for the program counter looks pretty basic but my brain is hitting the end of the line for the day I think I need to take a walk after this and let it all soak in.  The pc register issue described in paragraphs 3 and 4 is interesting I need to chase more of it down. Looking at all of this has led me to well over my hour desire and my brain hurts lots of new stuff to ponder even without to much link chasing I will reconvene this tomorrow and likely restart this program counter section with fresh eyes and hopefully a slightly better understanding of things if not I'll break from the read through and start chasing down the first sections answers. 

The beginning

Day 1

     Last night while cooking dinner I was listening to an old Triangulation podcast with Steve Gibson it was episode # 147 (If you're unfamiliar go here).  It was the second of a many part interview series and Steve's life has really struck a chord with me and has inspired me. I am planning on embarking on a journey to not only understand but also build a relay computer.  I have a lengthy background tooling around with various bits of tech and have an easy intuition for it but only in the past few years have I ventured into deeper learning and understanding of these things I love.  This blog may digress at times venturing into my PiDP8 kit build or various Raspberry Pi and Arduino projects but I promise to try and limit that exposure and when I do rant to try and keep it to the central theme of this particular project.  My goal is to work at least 30 - 60 minutes per day on this it will start as mostly research but will slowly morph into buying and building. I also intend to update this blog 3 times per week with a brief overview of what I have been up to most likely on Monday, Wednesday, and Saturday every week. right now I am reading through a build here and trying to wrap my head around it I will be posting my thoughts and direction about this later today or more likely tomorrow.

     That all said I have a basic grasp of logic circuits and Boolean algebra so much of this will come quickly to me personally and I hope to any readers also if not google is your friend or I will always strive to keep up with comments. A further overview of my personal background and exposure is going to makeup the rest of this post so if that's not what interests you then move to the next post I promise this will be the only time I bother to get this personal.

     I am no writer and I doubt this will be a very compelling read to anyone outside of those looking to do the same as I am or tech geeks that love these things. But if you chose to read along I will try not to be to boring or dry and to also stay on topic and not pander.

     I am a 34 year old geek I played D&D I know my way around a comic shop and Linux.  I am most familiar with the Windows ecosystem but since starting to play with the Raspberry Pi platform have rekindled the romance with the command line and Linux specifically. I cut my computer teeth on an old IBM and the Apple II's my school had I grew up fiddling with 286, 386, and the brand new super fast 486 processors. I never delved to deeply into any 1 thing but knew enough to be dangerous with all of them.  I played Doom and Wolfenstein 3D like so many others and had a blast with my new windows 3.11 Hewlett-Packard machine in 1994 with the beast of a 486 in it and a CD-ROM drive. I spent hours playing a game called Mega Race which few enough people have heard of that I as yet cannot find a copy or port of to relive that particular childhood memory. I was just getting started with actually using that particular PC when the power supply died and I set it aside in favor of other endeavors. During high school I studied electronics and found my passion for hardware building a simple blinking light circuit or astable multivibrator with a 555 was just as fun my senior year as it was my freshmen year. After high school life happened and I was busy starting an adult life having kids working multiple jobs and generally struggling to find free time to occupy my interests, so it was not until at nearly 30 I managed to begin making time for my personal pursuits again. My youngest son has shown an interest in the electronic side of things and my middle son has shown an interest in machinery and these are desires I have done my best to nurture and grow these desires. Now I am at a place in my life where I can pursue my own interests with relative freedom and ease and I always have the guise of teaching them how it all works to do it.  Where I stand now tech wise is pretty straight forward I am on Android for mobile support with an unlimited data plan that I use extensively. I have 3 windows PC's 1 of which is a hand built i7-4790k powered gaming box/media server running windows 10 and 2 laptops of lesser note for school and work purposes. I also have 3-6 Raspberry Pi's in operation right now 1 running a connected calendar for the household the others in various states of use for everything from bitcoin mining management to a dev environment for my son's Arduino and scratch projects. I am slowly building up a home automation system based around Smartthings, Hue, and home brew particle photon projects. Other upcoming or in progress projects I am working on is a lighting system for my hedgehog that imitates the sun's rising and setting, multiple android and web apps, a robotic shift location verifier for my jeep to gain remote start, and a PiDP-8 kit that Steve Gibson mentioned last spring on the Security now podcast. These projects combined with this 1 take up most of my free time but come warmer weather I will be making time to partake of my preferred outdoor activities.  So building may be somewhat slowed.