PC Jargon Explained

Want to make music with a PC but don't know which one to choose? Brian Heywood provides advice to guide you through the maze of jargon in your quest to set up your ideal PC‑based music system.

The IBM or ISA (Industry Standard Architecture) PC has a bit of an 'anorak'‑ish image when compared to either the Apple Mac or the Atari ST/Falcon personal computers. This image is undoubtedly due to the perceived business and technical bias of the PC, since by the very nature of the beast it is ideally suited to putting together specialised computer systems. For the musician, the bottom line is that to put together a MIDI system based around a PC, you need to make decisions that ST or Mac users wouldn't need to make until they require a far more advanced system. The glittering prize is that the PC computer musician has far more choice as to how their music system is configured.

With its 'open' architecture design, the PC is a very flexible and relatively cheap computer to use for music applications. The cheapness derives from the high degree of competition you get between the various manufacturers of PC hardware and the vast number of PCs sold, while the flexibility is generally due to the number of expansion cards available. The downside of the PC's flexibility is that you need to have more of an idea of what's going on 'under the bonnet' in order to choose the PC most suitable for your musical needs — and that's where this article is designed to help.

Choosing A Processor

The PC is actually a family of computers, which started life in 1981 with the introduction of the original IBM PC. This machine was based around an Intel 8088 microprocessor running at 4.77MHz and was designed to compete with the business computers of the time, namely 8‑bit CP/M computers with 64Kbytes of RAM running at 4MHz. Much to IBM's chagrin, the design was hijacked by other computer manufacturers who then produced PC 'clones'; these were not only cheaper, but usually better than the IBM original.

Since then, Intel have produced a series of processors (80286, 80386, 80486) which are derived from the original 8086 chip, becoming progressively faster and using larger data word sizes (ie. number of bits). In 1984 IBM introduced the PC‑AT (PC‑Advanced Technology), which is the basis of the Industry Standard Architecture (or ISA) used by most of today's PCs. The current head of the Intel family is the Pentium, which is a 32‑bit processor running at 60 or 66MHz. Incidentally, the only reason it's not called a 80586 is that Intel are not able to register a number as a trademark. The accompanying table (Table 1) shows the difference between the various processor chips.

Most desktop PCs come with between three and eight standard ISA slots, but it is important to check how many of these are already taken up with basic service cards such as hard disk controllers, video cards and the like.

It's all very well wittering on about the ancestry of the PC, but which processor do you need?

As always, it depends on what you want to do and what your budget is. Most MIDI applications don't require a great deal of processing power, so the only real advantage of a fast PC is to reduce the latency, ie. the time between a MIDI event occurring and it being detected by the PC. If you are looking for a cheap, second‑hand system or have an old 286 machine, then you can achieve satisfactory performance using a DOS‑based music application such as Voyetra's Sequencer Plus. If you want to run under Windows, this immediately ups the ante to a fast 386SX or 386(DX) PC due to the extra demands Windows places on the processor.

Deciphering Processor Jargon

There are a number of terms you will encounter which refer to the PC's processor, the most common being the SX/DX suffix on the processor number. When Intel introduced the 32‑bit 80386, they produced a variant called the 80386SX which only used a 16‑bit data path. This made no difference to the operation of the software, it just meant that 32‑bit values needed two memory reads by the processor, thus making the PC run slower than one using a full 80386 chip. The full version is usually referred to as a 'DX', but I don't believe this is an 'official' Intel designation. Confusingly, when it comes to the next generation 80486 processor, the SX and DX suffixes mean something entirely different — a 486DX processor has a 'built‑in' maths co‑processor while the 486SX has none. Intel haven't announced an SX version of the Pentium chip... yet.

486 Clock Doubling & Overdrive

Two other terms that you may see associated with 486‑based PCs are 'clock doubling' (DX2) and the inclusion of an Overdrive socket. Clock doubling is where the processor runs at twice the speed of its associated circuitry, theoretically giving you improved performance without having to have very fast memory, etc. So a 66MHz DX2 PC is really a 33MHz machine whose processor is playing in double time. In my opinion clock doubling is a bit of a con, since you don't gain full advantage of the higher clock speed under most conditions. You should get better performance out of a 50MHz DX than a 66MHz DX2 PC — but always check before you buy, as not all PC clone manufacturers and dealers go out of their way to tell you the whole truth in their advertising brochures! Intel are currently working on a triple speed (DX3) processor, which will undoubtedly suffer from the same problem.

The inclusion of an Overdrive socket on a 486‑based PC means that you should be able to upgrade to a cut‑down Pentium processor — the P24T — when they become available. The upgrade won't give you a fully featured Pentium system, due to changes in the basic processor architecture, but Overdrive does give you the option of improving the performance of a 486DX‑based PC without replacing the motherboard. Needless to say, Intel haven't produced any Overdrive compatible Pentiums yet, so you have to take it on trust that this will become a viable option at some future date.

Confused By Memories?

One of the most confusing aspects of the PC is the number of different ways of looking at the RAM (random access memory). This is due to historical reasons. The original PC had a fairly conventional design for its memory map: like CP/M — on which it was based — its program memory started from zero with the operating system placed at the top of the available RAM. Since part of the operating system was stored in ROM (Read Only Memory), which was placed at the top of the memory map (just below the 1Mb mark); this left a 'massive' 640Kilobytes (ie. just over half a megabyte) of usable RAM, exactly 10 times the maximum amount of RAM available using CP/M computers.

Time and technology moved on, of course, but the massive popularity of the PC and the requirement that old DOS software should still be able to run has meant that this basic memory map is still used today. In the days before Microsoft Windows, two competing systems — Expanded and Extended memory — were developed to allow DOS programs to use available memory above the 1Mb mark. With Windows‑based music programs you shouldn't need to worry about the type of memory being used, since Windows automatically provides memory management for its applications. The three types of memory are:

• Conventional memory.
• Upper Memory Blocks (UMBs).
• Extended and/or Expanded memory.

The conventional memory is the 640Kb of RAM that can be used directly by DOS programs; the Upper Memory Blocks are chunks of free RAM located between the top of DOS memory and the 1Mb point. Expanded and Extended memory is located above the 1Mb point and is used by DOS programs. DOS version 6 provides a nifty utility called MEMMAKER that will automatically optimise your PC's configuration for the RAM you have installed. It's worth buying DOS 6 for this feature alone. It's also worth noting that a PC's quoted memory capacity includes the 640K and the UMBs, so that a 4Mb PC will only have around 3Mb of Extended memory.

With Windows‑based music programs you shouldn't need to worry about the type of memory being used, since Windows automatically provides memory management for its applications.

Most modern PCs have their RAM fitted as SIMMs (Single In‑line Memory Modules), which are small circuit boards that plug into connectors on the motherboard. SIMMs are very easy to install yourself and upgrade if necessary, and seem to come in two types: 9‑chip and 3‑chip. I must admit that I've never had any joy with 3‑chip SIMMs, so I'd advise you to check what type is being supplied and whether it will work in your particular PC. SIMMs usually need to be installed in banks of two or four, and you need to ensure that they are fast enough for your machine; again if you check with the supplier, they should be able to tell what speed (usually quoted in nanoseconds, eg. 70ns) you need. It's worth shopping around for the best price; I usually look through the back pages of Windows magazine and spend some time on the telephone.

Card Tricks On The Buses

The final important section of the PC's motherboard is the 'expansion bus'. This is the set of connectors that allows you to plug in additional controller cards, interfaces and such‑like. The original PC had 8‑bit expansion slots while the PC‑AT increased this to 16 bits, whilst maintaining compatibility with the original 8‑bit cards. This PC‑AT bus design is now more commonly referred to as the ISA or Industry Standard Architecture bus.

The ISA bus usually transfers data at around 5Mb per second, although some motherboards allow you to increase this speed using the CMOS setup routines. It doesn't take much of a mathematician to see that this input/output (I/O) bus can become a bottleneck in the performance of the PC as a whole. So, to get a around this, some PCs are fitted with the VESA local bus (VL‑bus), which allows such devices as graphics adapters and network cards to take full advantage of the PC's speed. Another contender in the PC bus stakes is the PCI bus from Intel, which not only cures the speed problem but will give compatibility with the forthcoming Apple PowerPC.

Most desktop PCs come with between three and eight standard ISA slots, but it is important to check how many of these are already taken up with basic service cards such as hard disk controllers, video cards and the like. A PC with five slots looks less attractive if three of them are taken up by the disk controller, VGA, and serial/printer port.

There is an enhanced version of the ISA bus (EISA) that supports 32‑bit data transfer, but PCs fitted with these are pretty thin on the ground and only need to be considered for specialist applications.

Mass Storage

After the motherboard, perhaps the most important component of the PC is the hard disk sub‑system. Most PCs are supplied with AT‑bus or IDE drives, which allow you to install up to two drives. The IDE drive uses an extension of the PC's I/O bus and integrates the hard disk interface circuitry with the controller to give very cost effective mass storage. Most of the smaller desktop PCs will have the disk controller built onto the motherboard, but tower (ie. upright) and larger desktop machines tend to have a separate IDE card.

An alternative to IDE is to use SCSI (Small Computer Systems Interface) for your main hard disk, which is especially attractive if you want to buy a SCSI CD‑ROM drive. SCSI drives are traditionally more expensive than their IDE equivalents but the price differential is becoming less significant as SCSI becomes more popular on the PC (Macs have always used SCSI).

The Future

The PC has changed a lot since it was introduced in 1981 and in the process has become the most popular computer ever made. Microsoft say that there are now over 30 million Windows users worldwide — and since it has been estimated that there is a four to one piracy rate, this means that there are more like 120 million users out there! As for the future of the PC, Pentium‑based systems are just around the corner and will be able to handle those applications which need even more processing power than is available today, so there's still a bit of life in the old workhorse yet.