Chapter 2
| About the Macintosh Chapter 2 |
Now that you know the Macintosh basics, it's time to explain the difference between your computer's 'memory' and the information it can store.
Human beings both think with and remember with a single device - their brains. Computers aren't like that. They think with their 'memory' (yes, confusing, isn't it) but they store information on their internal hard disk.
When you switch your Macintosh off, its memory is wiped clean (it needs continuous electrical power to work). This means that you have to make sure whatever you were working on is stored on the hard disk before you switch off. When you switch your Macintosh on, it has to load its own operating system off the hard disk into its memory before it can work at all. Think of the hard disk as a filing cabinet and the memory as a working space which gets cleared whenever you leave (and the contents thrown out if you haven't filed them!)
Both the Macintosh's memory and its hard disk can handle a fixed maximum amount of data, depending on the machine's specification. And data is measured in Kilobytes (K) and Megabytes (Mb) - a Megabyte is 1,000 Kilobytes (strictly, it's 1,024 Kilobytes).
Macintoshes are sold with anything from 4Mb to 16Mb or more of memory, and hard disks that can store from 250Mb to 1000Mb or more of information. To put this in perspective, a word processing program might take up about 10Mb of storage space on the hard desk, and need about 2Mb of memory to work in while you are using it The text of a 300-page novel would take up only about 300-500K, while an illustrated document like this one might take up 15Mb.
Both the amount of memory your machine has and the size of its hard drive are important. The hard drive size tells you how much information you can store, while the memory size governs the complexity of the work you can do. Some programs require a great deal of memory to run. There is a program called Adobe Photoshop, for example, (used to touch up photographs for publication) which needs 16Mb of memory - or more - to work properly.
Memory is more usually called RAM, and it's a fact of life that few Mac owners have enough RAM. RAM is expensive to manufacture, and machines are usually shipped with the minimum amount to cut costs. You can increase the amount of RAM in your machine, though, speak to your local Mac dealer about the options.
RAM, megabytes and hard disks are all central computer concepts - now you know what they mean. Soon they'll be peppering your every sentence...
Your Mac's processor
So we know that a Mac stores information on its hard disk, and that it works with it in its memory - now we need to look at the processor.
Note that you'll also see the processor described as the CPU (Central Processing Unit) or even chip (after silicon chip).
The processor is your Macintosh's engine. The operating system uses the processor to carry out the countless millions of instructions necessary to perform even the simplest-looking task. While the operating system give's the Mac its identity or personality the processor governs its raw speed.
There are many Macintosh models on the market, and they use a variety of processors (even though they are all related). The simplest way to break Macintoshes up into categories is to do it according to chip type, and there are two families:
| 1. | PowerPC Macs. These are the latest models, and they use a brand new type of processor - the PowerPC - which is a lot faster than the older types. However, Apple have made sure that all the existing Mac software, printers and other gadgets work with the new machines, and the operating system looks just the same, and is the same to use. Most users won't notice any difference, apart from the extra speed. |
| 2. | Non-PowerPC Macs. These are older models which use processors manufactured by Motorola. This family of processors started way back in the 1980s with the 68000 model. Soon there was a faster version - the 68020, followed by the even-faster 68030 and finally the quickest of them all, the 68040. Machines based on the 68040 are not a lot slower than the cheapest PowerPC Macs, and because Apple have only recently stopped making them, you can pick up some excellent bargains from the mail order companies which advertise in computer magazines. |
On the whole, the processor type is the single most useful guide to the speed and power of a Macintosh. There are a couple of secondary considerations, though:
| 1. | Clock speed is the rate at which a processor carries out its myriad calculations per second. The clock speed is measured in cycles per second (the processor oscillates like the crystal in a quartz watch) - or MHz (megahertz). For example, the 68030 processor has been made available as a 25MHz model and a 33MHz model. Macintoshes with the 33MHz model are approximately 30% faster. Having said that, the slowest 68040 processor is still faster than the fastest 68030 model. Generally, the slowest model of any new processor is faster than the quickest version of the previous one. |
| 2. | RAM, or memory, is also a vital ingredient in speed. Many programs require a great deal of RAM to work efficiently. If they don't get it, they have to keep shuffling data from the hard disk into memory, and then back to the hard disk again to make room for fresh data. Moving data to and from the hard disk is slow, and having too little memory can ultimately slow you down far more than having a Macintosh with an 'old' processor. Before you upgrade your Macintosh to a faster model, make sure that the speed problems you're encountering aren't due to a lack of RAM. The easy check is to keep watching your hard disk light while you're using your applications, and to watch out for pauses when the display freezes up for a few moments. These are signs that the Mac is having to access its hard disk. This is normal when loading files stored there, but not when you're in the middle of working on one. |
Although non-PowerPC Macs will soon become hard to buy, there are so many in circulation that software manufacturers will be producing software for them for a long time to come. However, because the PowerPC processor works in a very different way to the older type, software designed specifically for it is much quicker than software designed for the older processors, so manufacturers are increasingly producing versions of their programs specifically for PowerPC based Macintoshes. These are called 'native' applications. If you have a non-PowerPC Mac, applications described as 'native' will not work. If you have a PowerPC Mac and you are offered a choice between a 68xxx version and a native version of a program, go for the native version.
Mac-spotting
Macintoshes are usually sold in two forms: standard machines and Performas. Performas are Macs specially designed for more inexperienced users and those using their Mac at home rather than in business. They are sold as complete packages, with practically everything you'll need to get started, and come with extra software and help for beginners. The standard machines, on the other hand, may be more expandable - it can be easier to add specialist hardware later on, and you have more choice over the equipment that comes with your machine.
There are too many different models and variations to list them all here, but with the help of this brief overview you should be able to recognise most types and decipher the specifications printed in magazines.
Expert tips
If memory's tight, you can save it by carefully running through your System Extensions (there's more on Extensions in chapter six). Using Extension Manager (included with System 7.5) or a third-party Extensions utility, you can pare down your extensions into minimal sets for specific jobs (if you're using a paint package, for example, you can probable manage without Adobe Type Manager, which is very RAM-hungry).
Although PowerMac-native versions of applications need more RAM than their 680x0 versions, a design quirk of the PowerMac means that switching on virtual memory makes the machine handle applications differently - they require a much smaller RAM allocation, frequently half as much. With 1Mb of virtual memory allocated, QuarkXPress, for example, runs in as little as 1.6Mb on a PowerMac.
On 680x0-based machines, don't use virtual memory if you can avoid it. You need all the speed you can get, and shuffling data that should be in RAM to and from your hard drive is highly inefficient. If you really can't afford the extra RAM, get hold of a copy of the excellent RAM Doubler from Connectix - it really does work, and with a minimal speed penalty.
Beware of RAM fragmentation! If you keep launching and quitting applications, your available RAM will get broken up into useless little segments - and applications need contiguous RAM to load into. If you hit unexpected memory problems, quit all your applications, then launch them all again - this will make them fill up the available memory without any gaps.
If you're having trouble running older applications, it could be that they're not 32-bit clean. The Mac's OS is fully 32-bit these days, but older software may have been written in the old days of 24-bit addressing. If you're running System 7, turn off 32-bit addressing in the Memory control panel and try again. If you're running System 7.5 - tough. Time to buy some new software.
Opinions are divided about the Disk Cache (Memory control panel). This is a segment of RAM that stores the last block of data taken from the drive on the assumption that it's quite likely to be needed again shortly. Everyone agrees that's a good idea, but what's not so well-known is that not everyone agrees the Mac's caching system is terribly smart. If you need more RAM, reduce the Disk Cache setting to 128K or even 64K. Many of the newer processors have their own caches, and some software has its own caching systems (interestingly, Photoshop and the Mac's Disk Cache can conflict badly).
G.Mills@compserv.gla.ac.uk