16K RAM Pack

ZX Computing

Tim Langdell

RAM, SWEET RAM In this review, Tim Langdell from West Dulwich looks at a number of RAM packs and assesses their value for the ZX81 owner. There's no special reason for our choosing these particular add-on memories, and they differ quite a lot in their price (from £20 to about £55) and in their facilities. They are aimed at different markets to some extent, and should not be directly compared without bearing this in mind. Hopefully, though, by discussing each of their features and quirks I may be able to give you some idea of what you might be looking for in a RAM pack. The main five RAM packs being considered are all 16K byte ones, although two of them have bigger 56K byte sisters (and I will mention these too). I'll also be comparing each of them with Sinclair's own 16K RAM pack to give you some idea of how they differ. The RAMs are from Bug Byte, Taurus, Downsway, Memotech, and Plessis. First, the original Sinclair memory pack. When this first came out it was the only one you could buy for your Sinclair computer, and at that time it was a compact, reasonably-priced design. However, most people who bought one of these RAM packs noticed that it buzzed when in use and did not like being moved or used for too long. Some of the Sinclair packs overheated quickly leading to a 'crash', and some needed only to be moved a fraction for the memory to be lost and the now infamous 'white out' to occur. Some people helped these problems by taking the RAM out of its case and using Vaseline on the rear connector but these modifications seemed a bit unnecessary. By the end of last year, RAM packs had hit the market which were more reliable than Sinclair's and didn't buzz. By the beginning of this year these RAM packs were also selling for some £10 less than the Sinclair, which more realistically reflected the drop in the cost of electronic components over the last two years. Now there are at least a dozen 16K RAM packs for the ZX81 on the market, and knowing which one to chose can be difficult. A price war seems to have started over the past three months to see who can sell a 16K RAM for least. One of the earlier RAM packs to be launched was Downsway's 16K one, although it was sold through Hilderbay, Buffer Micro Shop, and JRS. Now Downsway distribute RAM packs themselves and have added a 56K RAM to their range. Their 16K RAM pack is very small and light. It comes in a black plastic box with a gold plated edge connector protruding from the bottom. It is simple to slot into the rear of the ZX81 in the same way as the Sinclair RAM. However, it is lighter than the Sinclair and has a foam strip across it which reduces wobble (and hence potential crashes) to a minimum. Unlike the Sinclair (but like all the other RAMs in this review) Downsway's RAM did not buzz when in use. In fact, my main complaint (if not only) about it was that it had no duplicate edge connector at the rear of it, which means that it must either be the only add-on at the back, or at least the last to be added on. This is true of the Sinclair RAM pack too, of course, and many others as well. The Bug Byte RAM pack is a newer addition and true to its name is one of the biggest 16K RAMs on the market. Bug Byte claim that they put it in a large black plastic box to improve its stability. But this means that it is about three times the size of the Downsway RAM and not really any less stable, and I have my doubts about their reasoning. Nonetheless, it was also a reasonably stable RAM pack which ran happily for hours. Unlike other RAMs it has a power-on light-emitting diode which lights up to tell you the RAM is switched on. I must say that I did not see much point in this feature other than to remind you whether the whole computer is on or off. Should you be curious, 90 per cent of the inside of the Bug Byte is empty space... Memotech pioneered the big memory scene for the ZX81 when they brought out their 48K RAM extension last year. Even at about £125 this sold well and paved the way for the recent 56K byte RAMs which have suddenly appeared. Clive Sinclair envisaged ZX81 users adding no more than 16K bytes of RAM to their machine and at first it was said to be impossible to add more than this. The reason for this was that the ZX81 uses the address line 15 (A15) to produce the TV display and yet a logical high on this address line is what the ZX81 needs to detect when addressing memory space above the 32K mark. For the technical buffs the solution to the dilemma lies in realising that when the M1 line is low and A15 is high, a display is being generated, but if A15 is high at other times it must be because the line holds a valid address. No one, then, was too surprised to see Memotech produce another first with a 56K byte RAM early this year, but it was quite recently that they started offering a 16K RAM pack too. The new RAMs from Memotech are beautifully designed and blend in really well with the styling of the ZX81. They come in black anodised aluminium cases shaped to the contour of the rear of the ZX81, and therefore fit like a glove. There is virtually no wobble, but chances of wobble can be further reduced by using the foam strip which Memotech supply. Unlike almost all other RAM packs, the Memotechs have a duplicate rear connector coming out the back. It is thus quite easy to add more hardware on. Like all the other 16K RAM packs (with the exception of the Taurus) the Memotech one uses 4116 industry standard RAM chips and the whole assembly has a very professional feel to it. The 4116 RAM chips are each 16K bytes by one data line, and so eight are needed for a 16K RAM. But these chips whilst popular are not best suited for the latest micros. They need not only the usual 5 volts to run them but also a - 5 Vand 12 V supply. Makers had thus been waiting for the new 64K-by-one chips to come down to a reasonable price for these only need a single 5V supply, draw very little current, and you need only eight of them for a potential 64K bytes of memory! Memotech were the first to use these new 4564 chips, soon followed by others such as Downsway. Both the Memotech and Downsway larger memory packs are almost identical to look at as their 16K counterparts. The major difference between the Memotech packs is that the so called 64K version has four switches visible in its rear which allow you to switch out the area between 8K and 16K in the memory map in 4K blocks. This is an excellent idea and I hope other manufacturers will follow this lead. The microprocessor in the ZX81 (the Z80A) can only address 64K of memory and the first 8K of this is taken up with Sinclair's ROM (ReadOnly Memory) containing the software to run the machine, provided the BASIC and so on. Therefore the very biggest add on memory can only be 56K, and it was rather misleading of Memotech to refer to it as a full 64K RAM pack. To confuse matters, many other manufacturers copied Memotech's use of the term '64K RAM pack' just in case you though the Memotech one was bigger! Both the Memotech and Downsway 56K packs can be obtained by part exchanging your 16K RAM. Memotech give you three months to return your 16K Memopak for an upgrade, whereas Downsway seem happy to consider any 16K RAM in working order in part exchange. In use the big RAM packs are identical; giving 16K or RAM for BASIC programs, the top 32K area where you can store data, arrays, etc, and the 8K space between 8K and 16K where machine code can be run, or programs or data can be stored for transference between programs (this area of memory remains intact after NEW or after loading another program). It is important to remember, though, that with one of these bigger memories you have mapped all the available memory space leaving none for other add-ens to use such as character generators, sound boards, or memory mapped I/O ports. Only the Memotech allows you to add something between 8K and 16K, but many add-ens are mapped in the 32K region and are thus not usable. The RAM pack from Taurus offers the unique facility of either being a 16K RAM or a 14K RAM with a 2K monitor on EPROM (a form of ReadOnly Memory). Unlike all the other RAMs the Taurus fits to the ZX81 with a ribbon cable and is contained inside a black plastic covered aluminium box. There is a switch on the outside of the box to switch in and out the monitor facility. Because of the use of a ribbon cable to connect this RAM pack it is free from any problems of poor contact and wobbling. If you are interested in serious programming using machine code, then you may find the Taurus monitor very useful. I found some of its capabilities almost awesome, and nearly all of them very useful. Briefly, the monitor allows you to do hexadecimal arithmetic, set/clear/or display breakpoints, copy data from one area of memory to another, do decimal to hex conversion and vice versa, fill an area of memory with a constant, move the contents of one area of memory to another, read/write a port, display the state of the registers, display the contents of DFILE DFCC VARS and ELINE, write a REM statements of any length, tabulate the contents of memory, reset the stack pointer... and more. To give an idea of its capabilities. I wrote a REM statement of 2048 dots with one command to the monitor and filled the REM with the entire 2K of memory used by the monitor with another simple command - all in a matter of seconds. The usual method of typing in 2048 characters and running a FOR/NEXT loop to load the data into memory seems ridiculously slow by comparison. The RAM pack part of the Taurus uses the less well known 2118 low power RAM chips. The RAM performed perfectly well, but I did have a reservation about the availability of the chips should anything ever go wrong. Finally, a new RAM pack has just come into the market and is manufactured by Plessis Electronics. It has been introduced at the very low price of £19.95, undercutting the cheapest other RAMs by up to £10. It comes in a black plastic box similar to Bug Byte's, but about half the size. Like the other RAM packs it has a gold plated edge connector, and does not buzz when being used. Plessis seem to have succeeded in producing a reliable 'no frills' RAM pack which works well and is at a rock bottom price (in fact one wonders how they are making a profit). I would have preferred to see Plessis use a foam strip to reduce the chance of wobble, but that being said I had no problems with programs crashing either due to wobble or overheating. In terms of value for money the Plessis must take the prize, although by the time this review appears no doubt other RAMs will have been brought down to about the £20 to £25 mark. The Bug Byte worked well but was rather large than it needed to be and at around £30 had little to recommend it over the Plessis at about £20. Sinclair have just brought the price of their RAM pack down to about £30 too, and are no doubt partly responsible for the low price trend which began around the time of the Spectrum's launch. But even reduced in price there is little to recommend the Sinclair offering either for it is still more likely to overheat than the others and makes an annoying buzzing sound. The Downsway 16K RAM is a very neat, small one and fits very firmly onto the ZX81. It is still worth considering at around £25 as a strong competitor to the Plessis, and may of course be cheaper soon. Their 56K RAM pack at about £60 (£47.50 with a 16K pack traded-in) is good value and some £20 cheaper than its Memotech rival. However, there's no denying that the Memotechs are the best-styled and best made RAM packs on the market. It's questionable whether it is appropriate to put a Rolls Royce add-on onto a Model T (any-colour-as-long-as-its-black) microcomputer. The only real advantage of the larger Memotech (apart from its looks) was its facility to switch out the 8K to 16K area in 4K blocks. The 16K version, whilst beautifully made, seems to have little which would entice me to pay twice the price of the Plessis. The Taurus RAM pack is mainly of interest because of its integral montior on EPROM. The version of it as just a 16K RAM pack at about £46 really doesn't seem competitive. As the monitor is also available as part of an 8K EPROM board (mapped between 8K and 16K) it may be better to buy it in this form, or on cassette. At a guess I would say that the 16K RAM pack prices will now level out at about the £20 to £30 mark because at the present prices of the components involved and the companies' overheads they, cannot realistically be expected to bring the prices any lower. What we may see is a still further drop in the cost of the 64K RAM chips and as a result a drop in the cost of the 56K RAMs, too. In fact these bigger RAMs may become almost as I cheap as the 16K ones! In the end it boils down to asking yourself how much memory you need (16K is a lot) and what facilities, and then choosing a RAM pack which is in your price range and which hasn't been reported to have any obvious problems. Bug Byte 16K RAM pack, £31.95. From Caps Ltd, [redacted] or from Phoenix Marketing, [redacted]. Downsway RAM pack, 16K £24.95, 56K £69.95 or £47.45 with a 16K in part exchange. Downsway Electronics Ltd., [redacted] or from Buffer Micro Shop, [redacted]. Memopak 16K £39.95, Memopak 64K £79.00 or £55 with a 16K Memopak. Memotech Ltd., [redacted]. Plessis RAM pack £19.95. Plessis Electronics, [redacted]. Sinclair 16K RAM £29.95. Sinclair Research, [redacted]. Taurus RAM pack and monitor £54.95, just 16K RAM £45.95. Taurus Computer Design, [redacted]. My thanks are due to Buffer Micro Shop who lent me the Downsway RAM packs and allowed me to refresh my memory of the Sinclair offering. RAM pack prices are falling so rapidly it is likely that some of the above prices will be out of date. You are advised to check the advertisements in this issue of ZX Computing to get the latest prices.

The RAM pack and toolkit from Taurus.

Sinclair User

2K MONITOR EPROM Taurus Computer Design has a 16K RAM pack which also contains a 2K monitor EPROM for writing machine code programs on the ZX-81. It replaces the top 2K of RAM when the switch is thrown on the front of the RAM pack and you can enter the machine code monitor by a simple USR command. The monitor provides facilities such as hex arithmetic, break points, copying data from one place to another, decimal to hex conversion, fill, memory display, port read and write, plus many more. The monitor will write a suitable-length REM statement at the beginning of a program, so that your machine code routine can be stored there and will even re-set the Basic variables so that a RETURN from the monitor will not crash the program. All is contained in a metal box 5.5 x 2.5 x 1.5in, which attaches to the ZX-81 edge connector via a ribbon cable to prevent crashing the program, due to the movement of the ZX-81. The 16K RAM pack costs £59.95 with the monitor and £49.95 without, from Taurus Computer Design, [redacted].

The 16K RAM pack from Taurus Computer Design.