Microcomputers Interview Preparation Guide

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We designed the BBC machine using System 3s (I did a lot of character design work with a prototype System 80 column video card) and still had System 4/5 stuff going on in 1982 perhaps then.

Packing them in boxes (upstairs at 4a Market Hill): the whole company would stand around tables (a production square) and put in the right components (me, Hermann, Hermann?s then fianc? Stephen, Chris). We all did pretty much anything: I ended up as Hermann?s secretary before we could afford one!

There used to be problems with answering the phone: one chap would ring up and say ?I have got an Acorn, it does not work? often enough for it to become a legend. We got very tired of kits ? the highlight being a guy who assembled his Atom with glue because he knew that heat (solder) would damage them ? so that coloured the BBC machine a lot.

Summer holidays, 1978. Then I went home and drew circuit boards on the dining room table (and floor!) and wrote the manual. All by hand, of course.

Christmas 1978 I must have written System BASIC.

I had designed something similar for myself, and was in the process of helping Hermann [Hauser] with his ideas for an electronic pocket book (what we might nowadays call a PDA). In the course of showing that my designs for it would work, I showed him my schematics for my own machine and was challenged to build it. So I did With my own white ceramic 6502, too. That was just the equivalent of the CPU board of the System 1 with LEDs and keyboard (all on the same bit of Veroboard) the cassette interface was added later. I think Hermann was overly impressed when it worked first time!

Not exactly based on anything. Most of its heritage was from an automated cow feeder that Id designed for a Harrogate company the previous summer (1977). Quite an advanced thing, really it had a (waterproof) number pad, big 7 segment LEDs, OS in non-volatile EEPROM, and the trademark 6502. Both were from my own designs for something for myself, and they came from the aether.

The most hair-raising thing was the cow-feeders programme. I didnt own a PROM blower, so I had to write the whole thing by hand and send it off to a company who hand entered it into a machine and sent me back the PROM. That worked first time, too. Mind you, it was even smaller, being a boot loader that allowed the cow-feeders EEPROM to be initialised.

Actually, that came later. The initial work was done for Hermann?s own company ?Cambridge Processor Unit? (that?s an Austrian?s idea of a joke). Hermann went for the System One and came up somehow with the Acorn name, then Clive and Chris had an argument and Chris left Science of Cambridge and joined Hermann at Acorn: the first thing that we worked on with Chris was the Atom.

At the start, CPU had consultancy contracts for fruit machines. Initially these had been SC/MP based, but they got moved to 6502s. I was first approached by Hermann at a CUPG meeting ? he wanted someone who knew about low power technology, since he had this idea for a ?electronic notebook?. I designed an anti-theft device for the fruit machines (piezo lighters [were] being used to knock out electronic devices, so I put in a wideband radio receiver to stop the fruit machine paying out mistakenly: later on the acceptance test for the machine involved it being plugged into the same power line as an arc welder and sparks being struck ? it passed!). After that Hermann wanted to see my designs that might work for the electronic notebook and asked ?will it work?? ?Of course? ?so build it?.

When combined with other integrated circuits that provide storage for data and programs, often on a single semiconductor base to form a chip, the microprocessor becomes the heart of a small computer , or microcomputer.

Me for the bottom board. Me, Stephen Furber and maybe Kim Spence-Jones for the top board (cassette interface). (Hmmm ? maybe KSJ was a little later ? he certainly did some of the work on the analogue bits of the BBC machine cassette interface.)

During the time it was built! Hermann was very interested in it. It certainly worked before I went back to Yorkshire before the start of the term.

Because Hermann had them around: Science of Cambridge used 8154s on its MK14 kit (National SC/MP based) and so they were available when we needed something for the 6502. They were fairly cheap and the extra RAM was a bonus, even though it meant converting from 6502 clock/write to the read strobe/write strobe that they used.

Because it was there. Because it was new. Because a few of the other members of the Cambridge University Processor Group [CUPG] were going on about it being easier to interface to circuits. I guess I don?t really know precisely why I chose the 6502 ? maybe we just had an affinity!

It cost quite a lot back in 1977/78 when I bought mine ? which was a wonderful white ceramic part with gold (coloured?) legs and lid.

No bugs in the first, smaller, version of the software (256 bytes of code blown into PROM by Nick Toop?s PROM blower). There were a couple of problems with the cassette interface software because I got the order of bits the wrong way round (from the CUTS? standard). But hey, it was only 512 bytes: you can?t make any mistakes in that even when you write it by hand, hand assemble it and hand enter it into the PROM blower! Besides, it could debug itself to a fair extent (given that it basically worked).

Maths, followed by Computer Science.

The key elements of protocols are
a. Syntax:
It refers to the structure or format of the data, that is the order in which they are presented.
b. Semantics:
It refers to the meaning of each section of bits.
c. Timing:
Timing refers to two characteristics: When data should be sent and how fast they can be sent.

★ Unauthorized Access
★ Viruses

a) Number of Users
b) Type of transmission medium
c) Hardware
d) Software

a) Frequency of failure
b) Recovery time of a network after a failure

TDM is a digital process that can be applied when the data rate capacity of the transmission medium is greater than the data rate required by the sending and receiving devices.

★ Performance:
It can be measured in many ways, including transmit time and response time. ★ Reliability:
It is measured by frequency of failure, the time it takes a link to recover from a failure, and the network's robustness.
★ Security:
Security issues includes protecting data from unauthorized access and virues.

The Transport layer links the network support layers and user support layers.

★ Network redirector/ Server
★ Cache manager.
★ File systems
★ Network driver
★ Device driver

Also called FIFO anomaly. Usually, on increasing the number of frames allocated to a process virtual memory, the process execution is faster, because fewer page faults occur. Sometimes, the reverse happens, i.e., the execution time increases even when more frames are allocated to the process. This is Belady's Anomaly. This is true for certain page reference patterns.

★ Security/Encapsulation
★ Distributed database
★ Faster Problem solving
★ Security through redundancy
★ Collaborative Processing

In STDM, the multiplexer allocates exactly the same time slot to each device at all times, whether or not a device has anything to transmit.

Defining a useful channel involves both understanding the applications requirements and recognizing the limitations of the underlying technology. The gap between what applications expects and what the underlying technology can provide is called semantic gap.