Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84 exptools; site ihwpt.UUCP Path: utzoo!watmath!clyde!cbosgd!ihnp4!ihwpt!dafa From: dafa@ihwpt.UUCP (David Fay) Newsgroups: net.micro.mac Subject: Re: Re: 1.5 Meg Upgrade from MacMemory Message-ID: <523@ihwpt.UUCP> Date: Fri, 18-Oct-85 01:35:05 EDT Article-I.D.: ihwpt.523 Posted: Fri Oct 18 01:35:05 1985 Date-Received: Mon, 21-Oct-85 03:49:56 EDT References: <501@ihwpt.UUCP> <2092@amdahl.UUCP> <509@ihwpt.UUCP> <1201@wanginst.UUCP> Distribution: net Organization: AT&T Bell Laboratories Lines: 91 After talking further with MacMemory and with my hardware friends, I would like to clarify several issues discussed in my previous submissions on the MacMemory 1.5 Megabyte upgrade. As several people pointed out, I was confused about how screen memory location is determined. In fact, screen memory location is determined entirely by hardware address decoding. However, in order that programs can know about the location of screen memory, the ROM puts a pointer to it in the low memory location ScreenBase. This is done by figuring out how much memory the Mac has, and then assuming screen memory starts a certain distance below the top of memory. Currently, the ROM assumes that a Mac can have only 128K or 512K. If you increase memory beyond 512K, the current ROM will set ScreenBase incorrectly, so you must patch it to point to the actual location of the screen memory. This is done by the ROMs that Levco and others provide with their upgrades. The new Apple ROMs will not assume that memory can only be 128K or 512K. Instead, they will figure out how much memory is actually installed and then set ScreenBase appropriately. Megabyte upgrades that move screen memory to the top of physical memory have one disadvantage: they are more expensive. Extra circuitry must be provided for ROMs to override the Apple ROMs. Furthermore, when the Apple ROMs come out in a few months, these non-Apple ROMs will become vestigial. MacMemory has taken a different approach. They have built in the address decoding for locating screen memory to the top of 1.5 Megabytes (AND to the top of 4 Meg with 1 Megabit chips) but have not enabled the relocation in order to avoid the expense of the extra ROMs. When the new ROMs come out, all you have to do is to cut a trace on the board. Screen memory will then be at the top of 1.5 Meg and the Apple ROMs will set ScreenBase correctly. According to the designer of The Max board at MacMemory, who also happens to be Vice-President of Sales and Marketing there, they have already tried out the new Apple ROM with their board and, once the screen memory is relocated, it works fine. Because MacMemory saves the expense of new ROMs and because they have designed the board so as not to require a fan, they can offer significantly cheaper prices. Unfortunately, many of their employees are confused about what the prices actually are. On five separate phone calls, I and friends were given incorrect information about prices, some of which I reported in earlier articles. The correct prices for the KIT, according to the Vice-President, are as follows: List price: $525 Club price (quantity order, I believe): List minus 20% (~$420) Dealer prices: (quantity 2-4) $367 (quantity 5+) $324 So it looks like you can get one for about $420, which is the lowest 1.5 Megabyte upgrade available. The additional advantage, which I mentioned in an earlier article, is that you can upgrade to 4 Megabytes when megabit chips come out by making a further small modification to the board. This is a significant advantage in my view. One further unannounced advantage of MacMemory is that they will provide a free print spooler to all purchasers of the upgrade sometime next month. Finally, they offer a warranty on their board and (for additional money) a service contract on the whole Mac. They are negotiating with Apple right now for a deal like GCC worked out. If they can swing it, a MegaMac upgrade will not void your AppleCare and you will be able to get your Mac (except the daughter board I assume) serviced at an Apple dealer. Now the disadvantages: Until the Apple ROMs come out, you will be limited to 1 Megabyte of continuous memory and 512K of RamDisk (or vice versa). The upgrade is designed to be used with SOLDERED mother boards. So if you have upgraded to 512K yourself and used sockets, as I have, it's not clear The Max will work. We just received a board in the mail and will be reporting in the next few weeks whether the board has enough clearance to fit above a socketed motherboard. MacMemory also has some concerns about the extra inductance(?) added by the sockets. Finally, the 256K chips on the board are soldered, not socketed. This means you will have to desolder them to replace them with 1 Megabit chips. This is exactly analogous to a homebrew upgrade from 128K to 512K and should be no problem for someone handy with a soldering iron. -- -------------------- David Fay AT&T Bell Laboratories Naperville, IL 60566 ihnp4!ihexp!dafa